Performing Underchassis Preventive Maintenance

POWER STEERING HOSES - The primary purpose of power steering hoses is to transmit
power (fluid under pressure) from the pump, to the steering gearbox, and to return the fluid
ultimately to the pump reservoir. Hoses also, through material and construction, functions as
additional reservoirs and act as sound and vibration dampers.
Hoses are generally a reinforced synthetic rubber material coupled to metal tubing at the
connecting points. The pressure side must be able to handle pressures up to 1,500 psi. For that
reason, wherever there is a metal tubing to a rubber connection, the connection is crimped.
Pressure hoses are also subject to surges in pressure and pulsations from the pump. The
reinforced construction permits the hose to expand slightly and absorb changes in pressure.

Where two diameters of hose are used on the pressure side, the larger diameter or pressure
hose is at the pump end. It acts as a reservoir and as an accumulator absorbing pulsations, The
smaller diameter or return hose reduces the effects of kickback from the gear itself. By
restricting fluid flow, it also maintains constant back pressure on the pump, which reduces pump
noise. If the hose is of one diameter, the gearbox is performing the damping functions internally.

Because of working fluid temperature and adjacent engine temperatures, these hose must be
able to withstand temperatures up to 300oF. Due to various weather conditions, they must also
tolerate sub-zero temperatures as well. Hose material is specifically formulated to resist
breakdown or deterioration due to oil or temperature conditions.

Code No. Performing Underchassis Preventive Maintenance Date: Developed Date: Revised Page #
ALT723306
Oct. 26, 2003 May 24, 2004 50

Code No. Performing Underchassis Preventive Maintenance Date: Developed Date: Revised Page #
ALT723306
Oct. 26, 2003 May 24, 2004 51

SELF-CHECK LO3-1

Check your mastery of learning outcome #3 by completing this self-check.

1. What is power steering fluid?
a. used as a special power steering fluid
b. the steering axis inclination
c. caused by sagging springs
d. scrub radius

2. Steps to check steering fluid level
a. Open power steering reservoir cap, pull-out dipstick
b. tighten the power steering reservoir plug
c. loosen the power reservoir plug

3. Step to replace fluid level
a. open and drain steering fluid
b. tighten and close power steering drain plug
c. pull-out the power steering pump
d. install power steering pump

4. Step to refill power steering fluid
a. fill-up fluid to the power steering fluid
b. loosen bolt of power steering fluid
c. tighten bolt of power steering fluid
d. cut the hose

5. 5. What is the primary purpose of power steering hose?
a. to lubricate the pump
b. to relieve pressure
c. to transmit power through fluid under pressure
d. none of the above

Code No. Performing Underchassis Preventive Maintenance Date: Developed Date: Revised Page #
ALT723306
Oct. 26, 2003 May 24, 2004 52

ANSWER KEY LO3-1

1. A
2. A
3. A
4. A
5. C

Code No. Performing Underchassis Preventive Maintenance Date: Developed Date: Revised Page #
ALT723306
Oct. 26, 2003 May 24, 2004 53

Qualification Automotive Servicing NCI
Module Title Performing Underchasis Preventive Maintenance

Learning Outcome # 4 Check and refill automatic transmission fluid

Assessment Criteria : 1. Automotive transmission checked for leakage.
2. Automotive transmission fluid level checked in accordance

with service manual.
3. Transmission fluid refilled to specified level.

Resources :

1. Automotive Technology (manual) pp. 79-81

2. Modern Technical Physics pp. 292-294

3. Automotive Technology (training manual) pp. 12, 15

4. Modern Technology Physics, 6th edition pp. 268-275
Bieser, Arthur

5. The Auto Repair Book Doyle, John pp. 325-341

6. Nissan Diesel Chassis Repair Manual pp. 45-71

Code No. Performing Underchassis Preventive Maintenance Date: Developed Date: Revised Page #
ALT723306
Oct. 26, 2003 May 24, 2004 54

LEARNING EXPERIENCES

Learning Outcome #4 Check/refill automatic transmission fluid Resources
Learning Activity #1

Have you done checking for transmission leakage?
In this activity you will encounter different experiences as
you go along checking transmission leakage. Before you
do the checking, perform the following tasks:

1. Read: Resource to: Automotive Mechanics 10th
a. identify component parts of automatic edition, Crouse-Anglin, pp. 620-
transmission 630
b. understand the functions of each part.

Now that you know the component parts and functions
of automatic transmission, you can:

2. Read instructions to: Automotive Mechanics 10th
a. check automatic transmission leakage edition, Crouse-Anglin, pp. 640-
b. check the level of oil in accordance with the 645
service manual

3. Self-check #7 prepare task sheet

4. Refer to Model Answer #7

5. Call your Instructor to check your answers.

Code No. Performing Underchassis Preventive Maintenance Date: Developed Date: Revised Page #
ALT723306
Oct. 26, 2003 May 24, 2004 55

LEARNING EXPERIENCES

Learning Outcome #4 Check/refill automatic transmission fluid

Learning Activity #2 Special Instructions

After finishing checking automatic transmission fluid, Your Aside from the repair manual, you
next activity are to perform the following: can view video CD materials about
automatic transmission in your
1. Read: Repair manual and manufacturer's manual on resource center or library.
refilling ATF on automatic transmission.
Answer the provided Self Check
Perform refilling of ATF in automotive transmission in and ask your instructor to check
accordance with service manual. your answers.

If you pass the test, proceed to
actual refilling of ATF, then ask
your instructor to check your work.

Code No. Performing Underchassis Preventive Maintenance Date: Developed Date: Revised Page #
ALT723306
Oct. 26, 2003 May 24, 2004 56

INFORMATION SHEET LO4-1

Checking/Refilling Automatic Transmission Fluid

AUTOMATIC TRANSMISSION FLUID

Automatic transmission fluid is a special lubricant with about the same viscosity as an SAE 20
engine oil. It has several additives such as viscosity-index improvers, oxidation and corrosion
inhibitors, extreme-pressure and antifoam agents, detergents, dispersants, friction modifiers,
pour-point depressants, and fluidity modifiers. Automatic transmission fluid is usually dyed red.
This makes a leak more easily identifiable by its color.

There are several types of automatic transmission fluids. Each is compounded to work with
certain transmissions. Dexron-II is the most widely used. Type F is specified for some 1982 and
earlier Ford transmissions. Dexron-IIE is recommended for use in many electronically controlled
transmissions and transaxles. These fluids use shift solenoids and force motors with small oil-
flow passages. For proper operation, the fluid must not thicken excessively in low temperatures.
Dexron-IIE maintains the proper viscosity at low temperatures. It can also be used in other
automatic transmission for which Dexron-II isspecified.

TRANSMISSION FLUID COOLER

Overhead automatic-transmission fluid can damage the friction elements (bands and
multiple-disc clutches) in an automatic transmission or transaxle. The heat develops in an
unlocked torque converter and in other moving parts.

To prevent the fluid from overheating, automatic transmissions and transaxles have are
transmission-fluid cooler or oil cooler. It is usually a tube on the bottom or side of the engine
radiator.

The engine coolant runs at a lower temperature than the automatic-transmission fluid. As
the hot transmission fluid flows through the tube, the engine coolant carries away excess heat.
Cooler lines similar to steel fuel lines carry the transmission fluid between the case and the
radiator.

Code No. Performing Underchassis Preventive Maintenance Date: Developed Date: Revised Page #
ALT723306
Oct. 26, 2003 May 24, 2004 57

DISASSEMBLED VIEW (1)

Code No. Performing Underchassis Preventive Maintenance Date: Developed Date: Revised Page #
ALT723306
Oct. 26, 2003 May 24, 2004 58

DISASSEMBLED VIEW (2)

Code No. Performing Underchassis Preventive Maintenance Date: Developed Date: Revised Page #
ALT723306
Oct. 26, 2003 May 24, 2004 59

HYDRAULIC SYSTEM
Functions of the Hydraulic System

Figure below shows the complete hydraulic system of a 4-speed automatic transmission.The
hydraulic system provides the pressurized fluid to operate an automatic transmission or
transaxle. The hydraulic system:

Planetary gearset with clutch engaged. One set of clutch plates is splined to the sun-gear drum.
The other set is fixed to the planet-pinion carrier. When fluid pressure from the pump acts on
the apply side of the clutch piston (as shown), the clutch plates are forced together. This locks
the sun gear to the planet carrier and the planetary gearset rotates as a single unit.

1. Supplies fluid to the torque converter.
2. Directs pressurized fluid to the band servos and multiple-disc clutches.
3. Lubricates the internal parts.
4. Removes heat generated by the torque converter and other moving parts.

These four jobs are possible because the automatic transmission or transaxle is fitted with
automatic-transmission fluid (ATF). Without the proper amount of fluid, the transmission may
not shift and the vehicle may not move. Major components in the hydraulic system include the
oil pump, band servos, and multiple disc clutches. Other major components are the valve body
and governor.

NORMAL MAINTENANCE

Normal maintenance of an automatic transmission or transaxle includes:

1. Checking fluid level, color, and condition.
2. Adding fluid, if necessary.
3. Changing fluid and filter.
4. Checking shift and throttle linkage.
5. Adjusting neutral safety switch.
6. Adjusting bands, if possible.

The level of the automatic-transmission fluid (ATF) should be checked with every change of
engine oil. Many vehicle manufacturers recommend changing the transmission fluid and filter at
periodic intervals. The length of the intervals depends on how the vehicle is used. For example,
Chevrolet recommends changing the fluid and filter every 100,000 miles [160,000 km] for
normal service. For severe service, Chevrolet recommends changing the fluid and filter every
15,000 miles [25,000 km]. Severe service includes using the vehicle for trailer, tow or as a
delivery vehicle, police car, or taxi.

Code No. Performing Underchassis Preventive Maintenance Date: Developed Date: Revised Page #
ALT723306
Oct. 26, 2003 May 24, 2004 60

FLUID CHECKS

Checking Fluid Level and Adding Fluid

A check of the fluid level, color and conditions should be made at every change of engine oil. To
check the fluid level, drive the vehicle for 15 minutes or until the engine and transmission are at
normal operating temperature. Park the vehicle on level ground and firmly apply the parking
brake. Let the engine idle. Place the transmission selector lever in park (or NEUTRAL, if
specified by the manufacturer).

Clean any dirt from around the dipstick cap. Pull out the dipstick, wipe it, reinsert it, and pull it
out again. Note the fluid level on the dipstick. Touch the fluid on the end of the dipstick to get an
indication of fluid temperature. If the fluid feels cool, the fluid level should be on the low side of
the dipstick. If the fluid level feels warm or hot, (too hot to hold), the dipstick level should be on
the high side.

Fluid level will vary under normal operating conditions as much as ¾ inch [19 mm] from cold to
hot. For example, as the temperature of the fluid goes from 60°F [16°C] to 180°F [82°C], the
level of the fluid may rise to as much as ¾ inch [19 mm]. Some dipsticks are marked to show
proper levels at different fluid temperatures.

NOTE: On some automatic transaxles, the fluid level goes down as temperature increases. The
COLD mark on the dipstick is above the FULL mark. If the fluid level is low, add a sufficient
amount of the specified fluid to bring the level within the marks for the fluid temperature. Do not
overfill an automatic transmission or transaxle. Too much fluid will cause foaming. Foaming fluid
cannot operate bands and clutches properly. Then they will slip and probably burn. This could
result to a transmission or transaxle that needs an overhaul.

CHECKING FLUID COLOR

Automatic transmission fluid is normally red in color.
1. PINK FLUID – This indicates that the fluid cooler in the radiator is leaking. Engine
coolant has contaminated the fluid. Repair or replace the fluid cooler, and remove and
overhaul the transmission or transaxle. Replace the seals, bands, lined clutch plates,
nylon washers, and speedometer and governor gears. Coolant can affect these parts.
Clean all other parts and passages. Flush the cooler lines and flush or replace the torque
converter.

2. BROWN FLUID. ATF may turn dark in normal use. However, contaminated fluid may
also have a brown color. If the fluid appears contaminated, drain it then remove and
inspect the pan. A small amount of metal particles and friction material in the bottom of
the pan is normal. Replace the filter, and refill with new fluid. Large pieces of metal or
other material indicate excessive wear or failure. The transmission or transaxle should be
removed and overhauled. Flush the cooler lines and flush or replace the torque
converter.

Code No. Performing Underchassis Preventive Maintenance Date: Developed Date: Revised Page #
ALT723306
Oct. 26, 2003 May 24, 2004 61

CHECKING FLUID CONDITION

Fluid color and odor can be checked to determine the
condition of the fluid. Look at the color and smell the fluid
on the end of the dipstick. If the fluid is brown or black
and has a strong burnt odor, bands and clutch plates may
have slipped, overheated, and burned. Particles of friction
materials from the bands and clutch plates have probably
circulated through the torque converter, transmission, and
fluid cooler.

These particles can cause valves in the valve body to
stick. This may cause noisy, rough or missed shifts.
Slipping may occur because the servos and clutches
cannot work properly. A quick check of fluid condition can
be made by placing one or two drops of fluid from the end
of the dipstick on a paper towel. As the towel absorbs the
fluid, examine the stain for specks or particles.

This indicates solid material in the fluid. If the stain
spreads and is red or light brown in color, the fluid
probably is good. If the stain is dark and remains small,
the fluid is oxidized and should be changed. Oxidized
fluid has combined with oxygen in the air and no longer
has its original properties.

INSPECTING THE PAN

Gum or varnish on the dipstick, discolored fluid, and
particles or specks on the paper towel indicate the sump on pan should be removed and
inspected. A small amount of materials in the pan is normal. Look for large pieces of metal and
large amounts of friction material. These indicate abnormal wear or failure. The unit requires
rebuilding or overhaul.

Code No. Performing Underchassis Preventive Maintenance Date: Developed Date: Revised Page #
ALT723306
Oct. 26, 2003 May 24, 2004 62

CHECKING FOR FLUID LEAKS

When the dipstick shows a low fluid level, look for a
fluid leak. Some fluid can be lost through the case vent
if the fluid has foamed. To help locate the source of a
leak, automatic transmission fluid is usually dyed red.
This makes the leak easier to detect and identify.
Another method of leak detection is to use an
ultraviolet leak detector. If a leak detector is not
available, use the following procedure:

1. Clean the suspected area with solvents to remove
any traces of fluid.

2. Remove the torque-converter shield, if present and
expose as much of the torque converter as
possible. Inspecting the pan. A small amount of
material is normal. Large pieces of metal

Code No. Performing Underchassis Preventive Maintenance Date: Developed Date: Revised Page #
ALT723306
Oct. 26, 2003 May 24, 2004 63

SELF-CHECK LO4-1

1. What is automatic transmission fluid?
2. Identify the component parts of an automatic transmission.
3. Explain the functions of the parts of an automatic transmission.
4. Explain the procedure in checking automatic transmission fluid.
5. Explain the procedure in refilling automatic transmission fluid.

Code No. Performing Underchassis Preventive Maintenance Date: Developed Date: Revised Page #
ALT723306
Oct. 26, 2003 May 24, 2004 64

ANSWER KEY LO4-1

1. 1. Automatic-transmission fluid is a special lubricant with about the same viscosity as an
SAE 20 engine oil.

2. Parts of an Automatic Transmission

3. a. Automatic transmission is a transmission in which gear ratios are changed or adopts to
speed automatically when the accelerator pedal is pressed.

.
b. Automatic transmission is the same whether for rear-wheel drive, front-wheel drive or four-

wheel drive vehicles. Most automatic transmission has three or four forward speed. They
also have PARK, NEUTRAL, and REVERSE.

4. Pull out the dipstick, wipe it, reinsert it, and pull it out again. If fluid feels cool, the fluid level
should be on the low side of the dipstick. If fluid feels warm or hot (too hot to hold) the dipstick
level should be on the high side.

5. Fluid level will vary under normal operating conditions as much as ¾ inch (19 mm) from cold to
hot.

Code No. Performing Underchassis Preventive Maintenance Date: Developed Date: Revised Page #
ALT723306
Oct. 26, 2003 May 24, 2004 65

Qualification Automotive Servicing NCI

Module Title Performing Underchasis Preventive Maintenance

Learning Outcome # 5 Inspect and bleed air tank

Assessment Criteria : 1. Data pertaining to air tank obtained
2. Air tank inspected for moisture and leakage
3. Air tank bleed/drained of accumulated water.

Resources :

1. NISSAN DIESEL ENGINE Repair manual
(model PD and PDT)

2. Excellence in Automotive Glencoe Mc Grow pp. 118-119
hill

Code No. Performing Underchassis Preventive Maintenance Date: Developed Date: Revised Page #
ALT723306
Oct. 26, 2003 May 24, 2004 66

LEARNING EXPERIENCES

Learning Outcome #5: Inspect/bleed air tank Resources
Learning Activity #1

Have you inspected and bled an air tank?

1. Read: Resource on the procedure of inspecting and Nissan Diesel Engine
bleeding air tank. Repair Manual Model PD and
PDT, pp. 6- 12 to 6-14.
1.1 Prepare tools needed for inspecting and
bleeding air tank

1.2 Follow correct procedure in performing these
tasks.

2. Complete: Checking air tank, applying pressure, Data checklist provided
volume and temperature. experiment on vapor to liquid
state, Excellence in Automotive
3. Self-Check #8. by Glen Grace Hill, pp. 118-
119.
4. Refer to Model Answers #8.

5. Call your instructor to check your answers.

After performing the first activity, you can now do the Nissan Diesel Engine Repair
second activity. Manual, pp. 6-14

1. Read: Resource on the principles/procedure in Change from vapor to liquid.
bleeding air tank considering:

1.1 proper use of personal protective equipment
(PPE)

1.2 hazards in bleeding air tank.

2 Complete: Checking/inspecting moisture and
leakage.

3 Call your instructor to check your work.

Code No. Performing Underchassis Preventive Maintenance Date: Developed Date: Revised Page #
ALT723306
Oct. 26, 2003 May 24, 2004 67

LEARNING EXPERIENCES Resources

Learning Outcome #5: Inspect/bleed air tank Nissan Diesel Engine Repair
Manual, pp. 6-6 to 6-14
Learning Activity #2

This is the final activity for LO#5. In this
activity, you are going to:
1. Perform the procedure in bleeding an air tank

considering:

1.1 proper use of personal protective equipment
(PPE)

1.2 hazards associated in performing the task.

1.3 drained accumulated water.

2 Check air tank's pipes, hoses and clips.

3 Call your instructor to check your work.

Code No. Performing Underchassis Preventive Maintenance Date: Developed Date: Revised Page #
ALT723306
Oct. 26, 2003 May 24, 2004 68

INFORMATION SHEET LO5-1

Inspecting/Bleeding Air Tank

DESCRIPTION AND OPERATION
GENERAL AIR BRAKE SYSTEMS

The air brake system consists of three sub-systems; the air supply system, the air delivery
system, and the parking/emergency air brake system. The components making up the brake
system of each vehicle may differ, but all systems operate in basically the same manner.

All models use a vertically split brake system. If a failure occurs in the front brake system, the
rear brake system will continue to operate and give reduced stopping capability until the air
supply is depleted.

In the event of a failure in the rear system, the relay valve modulates application of the rear
spring brake units and the front brakes continue to function.

AIR SUPPLY SYSTEM
The air supply system is the source of air pressure for the brake system. It consists of a
compressor, reservoirs, governor, low pressure indicator, depth gauge, safety valve, drain
cock/automatic moisture ejector valve and tank charging valve.

The compressor is engine driven and controlled by a governor. When reservoir air pressure
reaches 793-861 kPa (115-125 psi), the governor cuts out the compressor. When reservoir
pressure drops to 82-179 kPa (12-26 psi) below the cut-out pressure, the governor allows the
compressor to cut in again. When reservoir air pressure drops below 353 kPa (60 psi), the low
pressure indicator valve closes an electrical circuit to the warning buzzer and the warning light.
If the air reservoir pressure exceeds 1034 kPa (150 psi), the safety valve will release the
pressure.

The air reservoirs are equipped with manual drain valves and/or an automatic moisture ejector
valve which can be drained for the removal of moisture from the air brake system.

AIR DELIVERY SYSTEM
The air delivery system delivers the air brake pressure from the air supply system to the brake
chambers. It controls the amount of air pressure that is delivered to the brake chambers, and
thus controls the amount of braking during a stop. It consists of the foot control valve, the relay
valve, quick release valve, and the brake chamber.

AIR STORAGE SYSTEM
A number of variations have been incorporated into the air storage system of Louisville models
however they may be broadly classified thus:

• Two tank system with emergency release - introduction (1975) to august 1980.
• Two tank system less emergency release - August 1980 to 1983 Model Year.
The two tank system has the primary tank on the vehicle right hand side and secondary on the
left.
• Three tank system 1983 Model Year.
The three tank system uses a dust compartment reservoir on the right hand side, the smaller
(rear) tank acting as a "wet tank" by cooling and condensing contaminants. Air operated
equipment should not be connected into the "wet tank".

Code No. Performing Underchassis Preventive Maintenance Date: Developed Date: Revised Page #
ALT723306
Oct. 26, 2003 May 24, 2004 69

The above is a simplified statement of design levels, changes in pipe and hose diameters and
routing and valve positioning will be evident on inspection of various models.
Refer to diagrams in this section for general layout.

PARKING/EMERGENCY SYSTEM
The parking brake system is composed of a parking brake control valve, a relay or double
check valve (tractors), quick release valves and spring brake chambers. The spring brake
chambers use a powerful spring to mechanically apply the brakes when air pressure is not
available (provided the brakes are properly adjusted).

Air pressure releases the spring brake chamber when the vehicle is moving. The air pressure is
delivered to the spring chamber by a relay valve or a double check valve which is controlled by
an air pressure signal from the control valve on the instrument panel. The relay valve or double
check valve also functions to prevent the application of the spring brakes and service brakes at
the same time thus preventing brake system damage.

TRACTOR/TRAILER AIR BRAKE SYSTEM
The tractor trailer air brake system is standard on 9000 models. Its function is to provide air
supply to the trailer for its braking system and control the trailer brakes during normal and
emergency stops. It also protects a tractor's brake system should a failure occur in the trailer's
air system and provides operation of the trainer brakes independent of the tractor brakes. The
following components are part of this system: tractor air supply control valve, tractor protection
valve, trailer brake hand control valve and the hoses, hanger and connectors.

Air pressure from the reservoir to the reservoir port of the governor forces the piston to
overcome the resistance of the pressure setting spring. (The piston and the inlet and exhaust
valve move up when reservoir air pressure reaches the governor cut-out setting.) The exhaust
stem seats on the inlet and exhaust valve thus opening the inlet passage. Reservoir air
pressure then flows by the open inlet valve, through the passage in the piston and out the
unloader port to the compressor unloading mechanism.

As air pressure in the reservoir drops to the governor cut-in setting, the force exerted by air
pressure on the piston will be reduced so that the pressure spring will move the piston
downward. The inlet valve will close and the exhaust valve will open. With the exhaust valve
open, air in the unloader line will escape through the exhaust stem and out the exhaust port.

Some governors am mounted directly to the compressor, allowing direct connection between
the compressor unloader and the governor unloader port.

SAFETY VALVE
The Safety Valve protects the air brake system
against excessive air pressure build up. The safety
valve consists of a spring loaded ball valve subjected
to reservoir pressure which will permit air to exhaust
the reservoir pressure to the atmosphere if reservoir
pressure rises above the valve pressure setting
which is determined by the force of the spring. A
safety valve setting of 1034 kPa (150 psi) is used and
is not adjustable.

Code No. Performing Underchassis Preventive Maintenance Date: Developed Date: Revised Page #
ALT723306
Oct. 26, 2003 May 24, 2004 70

Should system pressure rise to approximately 1034 kPa (150 psi) air pressure would force the
ball vent off its seat and allow reservoir pressure to vent to the atmosphere through the exhaust
port in the spring cage.

When reservoir pressure decreases sufficiently, the spring forc e will seat the ball check valve,
sealing off reservoir pressure. This occurs at 930 kPa (135 psi) for the 1034 kPa (150 psi)
setting. It is important to note that the desired pressure setting of the safety valve is determined
by the governor cut-out pressure. The opening and closing pressures of the safety valve should
always be in excess of the governor cut-out pressure setting. The pressure setting is stamped
on the lower wrench flat of the valve.

Normally, the safety valve remains inoperative and only functions when reservoir pressure rises
above the setting of the valve. Constant 'popping off' or exhausting of the safety valve can be
caused by a faulty safety valve, governor compressor unloader mechanism, or a combination of
any of the preceding items.

AUTOMATIC MOISTURE EJECTOR
VALVE (Typical)
The Automatic Moisture Ejector Valve (Fig.
4) expels moisture and contaminants from
the air system reservoir. It operates
automatically from ascending and
descending reservoir pressures and
requires no control from other sources. The
automatic moisture ejector valve may be
drained manually by depressing the stem
wire located in the exhaust port.
The elector valve has a die cast aluminum
body and cover, and is mounted in the
bottom or lower end port of the air system
reservoir. Automatic Moisture Ejector Valve

With no air pressure in the system, the inlet
and exhaust valves are closed. Upon charging the air system, a slight pressure opens the inlet
valve which permits air and contaminants to collect in the sump. The inlet valve remains open
when pressure is ascending in the system until (governor) cut-out pressure is reached. The
spring action of the valve guide in the sump cavity closes the inlet valve. The inlet valve and the
exhaust valve are now closed.

When reservoir pressure drops approximately 13 kPa (2 psi), air pressure in the sump cavity
opens the exhaust valve and allows moisture and contaminants to be ejected from the sump
cavity until pressure in the sump cavity drops sufficiently to close the exhaust valve.

The length of time the exhaust valve remains open and the amount of moisture and
contaminants ejected depends upon the sump pressure and the reservoir pressure drop that
occurs each time air is used from the system.

To drain the valve manually, use a tool to move the wire in the exhaust port upward and hold it
in until draining is completed to 0 kPa (0 psi).

Code No. Performing Underchassis Preventive Maintenance Date: Developed Date: Revised Page #
ALT723306
Oct. 26, 2003 May 24, 2004 71

LOW PRESSURE INDICATOR SWITCH
Low pressure indicator switches are located in both the primary and secondary air supply lines.
The switches operate a warning buzzer and a light in case of low air pressure.

TANK CHARGING VALVE
A valve is provided in the supply reservoir to allow air pressure to build up in the brake system
from an external air source. The tank valve is similar to a tire valve stem and operates similarly.

AIR GAUGE
Air Brake systems are dual circuit type which provides an emergency brake system, primary or
secondary service circuit, should a failure occur in any part of the brake system. The air gauge
provides a direct reading of each service system's air pressure.

PRESSURE PROTECTION VALVE -- PR-3
The pressure protection valve is a normally closed,
pressure control valve which can be referred to as a
non-exhausting sequence valve. An example would be
in an air brake system to protect on reservoir, or
reservoir system from another, by Closing automatically
at a preset pressure should a reservoir system failure
occur. The valves can also be used to delay filling of
auxiliary reservoirs to ensure a quick build-up of brake
system pressure. Air entering the supply port is initially
prevented from flowing out the delivery port by the inlet
valve which is held closed by the pressure regulating
spring above the piston.

When sufficient air pressure builds beneath the piston to overcome the setting of the regulating
spring, the piston will move, causing the inlet valve to unseat (open), and allow air to flow out
the delivery port. As long as air pressure at the supply port and beneath the piston remains
above the specified closing pressure, the inlet valve will remain open.

SINGLE CHECK VALVE
Single check valves protect the primary
and secondary air reservoirs against air
pressure loss in the compressor, the
supply tank against a loss of either
primary or secondary system pressure by
protecting the remaining system's
operation, and allow an emergency stop.

The single check valve is located in the air
line from the supply tank to each reservoir. It allows air to flow in one direction only and
prevents the flow of air in the reverse direction. Air flow in the normal direction moves the check
valve disc from its seat (Fig. 6), and the flow is unobstructed. Flow in the reverse direction is
prevented by the seating of the disc, which is caused by a drop in the up-stream all pressure
and assisted by the spring.

Code No. Performing Underchassis Preventive Maintenance Date: Developed Date: Revised Page #
ALT723306
Oct. 26, 2003 May 24, 2004 72

FOOT CONTROL VALVE (E-7)

The foot control valve is mounted to the dash panel
and uses a suspended pedal. It is of the dual brake
valve type which provides two separate circuits to
control the primary and secondary systems of the dual
or split systems.

Dual foot control valves are connected to each of the
air supply systems. The all from supply tanks is
metered by the foot control valve as the driver applies
the pedal during a brake stop. The metered air
pressure is then delivered to a rear axle relay valve
which controls the amount of air to the brake
chambers. This amount of air is proportional to the air
delivered from the foot valve air.

The front brakes are supplied directly from the foot
control valve.

RELAY VALVE TYPE R-6

The relay valve is an air actuated, graduating
directional control valve of high capacity and fast
response. Upon receipt of signal pressure from the
service brake valve, it will graduate hold and release
air pressure from the brake chambers to which it is
connected.

MODULATING VALVE (R-7)

This valve performs four functions:
1. Limits an adjustable hold-off pressure to the spring

brake actuators.
2. Provides for quick release of air pressure from the

spring cavity of the spring brake actuator allowing
fast actuator application.
3. Modulates the spring brakes through application of
the foot brake valve in the event of loss of rear axle
service brake pressure, This action takes
advantage of the driver's natural reaction to apply
the foot brake valve in an emergency brake
situation and eliminates the need to actuate dash
mounted controls.

Code No. Performing Underchassis Preventive Maintenance Date: Developed Date: Revised Page #
ALT723306
Oct. 26, 2003 May 24, 2004 73

BRAKE SERVICE AIR CHAMBER

The air system on air vehicles with spring actuated rear wheel parking brakes is equipped with
a tank valve for connection to an outside air supply, This valve permits the system to be re-
charged with air from an outside source, releasing the spring actuated parking brakes. This
enables the vehicle to be towed in an emergency.
Outside air source can be used only if the protected system is in operating condition.

The brake chamber assembly consists of two separate air chambers, each with its own
diaphragm and push rod. The service brake chamber applies the brake by air pressure and
releases it by spring pressure when air is exhausted. The parking or emergency brake is
applied by spring pressure and is released by air pressure.
Diaphragms should be replaced every 80,000 km (50,000 miles) or every 12 months.
Compressed air, admitted to the brake chamber, enters the chamber behind a dLm3hraoPa
which forces the push plate and push rod outward. On cam-type air brakes, the outward
movement of the push rod rotates the slack adjuster which rotates the brake camshaft and cam,
forcing the shoes against the drum. Air pressure delivered to the air chambers (delivered
through the inlet port) acts on the diaphragm, thus moving the push rod and plate. The amount
of force coming from the chamber is equal to the air pressure multiplied by the effective area of
the diaphragm.
This force is proportional to the air pressure delivered to the chambers.

WARNING: The very strong spring in these
units is highly compressed and can cause
serious, even fatal, injury if the spring is
released without control. Do not remove
chamber clamp before the spring is caged.
Install release tool in spring plate and tighten
down to cage the spring.

REAR SPRING BRAKE CHAMBER
Spring brakes are a dual purpose device
containing both a Service Air Brake Actuator
and a Spring Mechanism for positive parking
and emergency use. Application is by driver
control or automatic at a predetermined
service brake air system pressure.

As Parking Brake - Once applied, spring brakes cannot be released unless adequate air
pressure is available to operate the service brakes.

As Emergency Brake - Spring brakes are capable of stopping a moving vehicle if there is a
failure in the normal service brake air system.

Code No. Performing Underchassis Preventive Maintenance Date: Developed Date: Revised Page #
ALT723306
Oct. 26, 2003 May 24, 2004 74

SPRING BRAKE ACTUATOR OPERATION
A spring chamber incorporating a powerful internal
spring and an operating piston is installed in place of the
pressure plate of the service brake actuator. Its purpose
is to apply the brake mechanically, by means of the
spring and piston, to act as a parking brake.
The piston bears against the outer side of the service
brake diaphragm via a push rod and applies the brake
by allowing the spring pressure to move the service
actuator push rod in the same way as when the service
brake is operated.
When the parking brake control is moved to the 'OFF'
position, air is fed into each spring chamber to the
underside of the piston. The piston moves under the air
pressure, compressing the spring, and so releases the
brake. The spring is held in the compressed position as
long as the control remains in the 'OFF' position and
there is sufficient air pressure in the system. When the
parking brake control is moved to the 'PARK' position
the air in the spring chambers is released through quick
release valves and the springs re-assert themselves to
apply the brakes.

Manual Release
The spring pressure can be wound-off, by a threaded
bolt on each spring chamber, to allow the vehicle to be
moved in an emergency, when there is a system failure
or low air pressure, or to dismantle the brakes for repair.
When the parking brake is 'OFF' the service brake part
of the actuator will operate normally for service brake
application.

The Emergency Spring Brake Release Reservoir and
Control Valve
The function of this reservoir (3rd tank) is to provide
sufficient air to release the spring (park) brakes at least
twice after they have automatically applied because of a
failure on the air supply side of the park brake control
valve (e.g. compressor drive failure) and so allow the
vehicle to be moved to a place of safety for repair. In its
normal operating condition the emergency spring brake
release valve allows the blended park brake supply
circuit air to pass unhindered to the park brake control to
provide release pressure in the spring brake unit. To
release the spring brakes after a blended air supply
failure, depress the emergency release valve knob. The
failed supply circuit will now be closed off at the valve
and air from the emergency release tank will be routed
through the valve to the park brake control and be available to release the brakes.

CAUTION: The only braking available with the system in this condition is by the park brake control. Use
only to move the vehicle to safety.

Code No. Performing Underchassis Preventive Maintenance Date: Developed Date: Revised Page #
ALT723306
Oct. 26, 2003 May 24, 2004 75

QUICK RELEASE VALVE
The quick release valve reduces the time required
to release the brakes by hastening the exhaust of
air from the brake chambers or valves. The valve
body contains a diaphragm which permits supply
pressure from the control valve to flow through the
quick release valve to the brake chambers. When
control pressure is reduced, the air which has
passed through, escapes rapidly through the
exhaust port, rather than back through the brake
valve.

DOUBLE CHECK VALVE
Double Check Valves are used in an air brake
system to direct a flow of air into a common line
from either of two sources, whichever is at the
higher pressure. They may be used for directing
air flow for specific functions or to select the higher
pressure of either of two sources of air as a supply
source.
It is used with the tractor hand control valve to
allow either foot brake control or hand brake
control valve applications of the trailer brakes.
The double check valve operates as follows: air under pressure enters either end of the double
check valve (supply port). The moving shuttle responds to the pressure and seals the opposite
port, assuming it is at a lower pressure level than the other. The air flow continues out the
delivery port of the double check valve.

The position of the shuttle will reverse if the
pressure levels are reversed.

VM1 - TRACTOR/TRAILER VALVE (Where fitted)
The VM1 valve is a combination of two double
check valves and a tractor protection valve.

With this valve either of the two service brake
circuits of the dual air system on the vehicle can
be used to apply the trailer brakes. In addition the
VM1, when used in conjunction with a control
valve such as the PP-3/7, can open and close the
trailer service and supply hoses in the same
manner as a tractor protection valve.

Code No. Performing Underchassis Preventive Maintenance Date: Developed Date: Revised Page #
ALT723306
Oct. 26, 2003 May 24, 2004 76

The VM1 prime mover or tractor protection
manifold is located on the air manifold and
performs three main functions.

1. In conjunction with the prime mover or
Tractor Protection Control Valve it provides
manual or automatic shut off of air to the
trailer brake system. When the control valve
is in the manual position air supply to the
trailer system is cut off. When the control
valve is placed in the automatic position air
supply to the trailer system is shut off should
there be a sudden drop in air pressure on
the trailer side of the primer mover or tractor
protection manifold, as with a trailer
breakaway.

2. The second function of the prime mover or
tractor protection manifold is to permit
operation of the trailer brakes from either the
prime mover/tractor primary or secondary
circuit. As long as both prime mover or
tractor air circuits are in operation, blended
air from both circuits, which is supplied by
the prime mover/tractor brake valve, will be
supplied to the trailer brakes, Should either
prime mover/tractor air circuit malfunction,
the prime mover/tractor protection manifold
would provide pressure from the operating
air circuit to the trailer.

3. The third function of the prime mover/tractor
protection manifold is to permit independent
control of the trailer brakes by means of a
hand control valve located on the steering
column.
The prime mover/tractor protection manifold
also includes connections for service
stoplights and trailer emergency stoplights.
The functions of the double check valve and
the trailer emergency breakaway valve have
been incorporated in the prime mover/tractor
protection manifold.

CONTROL VALVE (PP-3/7)
The PP-3/7 push pull control valve is a
pressure sensitive, manually operable, on-
off control which will automatically return to
the exhaust position when manual force is
removed and supply air pressure is below
the required minimum.

Code No. Performing Underchassis Preventive Maintenance Date: Developed Date: Revised Page #
ALT723306
Oct. 26, 2003 May 24, 2004 77

Qualification Automotive Servicing NCI
Module Title Performing Underchasis Preventive Maintenance

Learning Outcome # 6 Check tire and tire pressure

Assessment Criteria : 1. Tire inspected for unwanted solid object.
2. Tire inspected for wear and deformities in accordance with

manual.
3. Cause of abnormal tire wear determined.
4. Tire pressure check in accordance with manufacturer’s

specification.

Resources :

1. Automotive Mechanics 1oth edition, Crouse- pp. 749-753
Anglin;

2. Auto Repair. John Doyle; pp. 297-298

3. The Automotive tire drive trains and chassis pp. 118-121
unit; Felizardo Y. Francisco;

4. Modern technical Physics; Arthur Bieser pp. 382-384

5. Matter and chemistry pp. 106-107

6. Modern technical Physics; Arthur Bieser; pp. 268-269

7. Automotive Mechanics; 10th ed, Crouse- pp. 757-763
Anglin;

Code No. Performing Underchassis Preventive Maintenance Date: Developed Date: Revised Page #
ALT723306
Oct. 26, 2003 May 24, 2004 78

LEARNING EXPERIENCES

Learning Outcome #6: Check tire and tire pressure Resources
Learning Activity #1

You've encountered problems while inspecting/bleeding
air tank, haven't you?

In this activity, you are going to learn about tires following Automotive Mechanics 10th
manufacturer's specifications edition, Crouse-Anglin, pp. 749-
753
1. Read: Resource on identifying the following:
1.1 purpose of tires
1.2 bias and radial plies
1.3 tire tread
1.4 tire valve

2. Read: Resource on inspecting tire for unwanted solid Prepare task sheet
object.
2.1 inspect tire for solid unwanted object
2.2 determine tire air pressure, temperature and
volume
2.3 record tire rotation

3. Self-Check #8

4. Refer to Model Answers #8

5. Call the instructor to check your answers.

Code No. Performing Underchassis Preventive Maintenance Date: Developed Date: Revised Page #
ALT723306
Oct. 26, 2003 May 24, 2004 79

LEARNING EXPERIENCES

Learning Outcome #6: Check tire and tire pressure Resources
Learning Activity #2

After performing the first activity, you are now going to
inspect tire for wear and deformities in accordance with
manufacturer's manual.

1. Read: Resource on causes of tire wear and The Automotive Drive Trains and
deformities. Chassis Unit, Felizardo Y
Francisco, pp. 118-121
2. Perform correct procedures in inspecting tire for wear
and deformities considering proper use of personal Modern Technical Physics, Arthur
protective equipment, proper handling of tools and Bieser, pp. 382-388
equipment. Matter and Chemistry, pp. 106-
107
3. In inspecting tire, determine causes of abnormal tire
wear.
3.1 Read:
- ideal gas flow
- polymers

4. Call the instructor to check your answers.

Consider the next activity and find out the science Modern Technical Physics by
concept relevant to the pressure gauge. Bieser, pp. 268-269.

1. Perform actual checking of tire pressure in Automotive Mechanics 10th
accordance with manufacturer's manual. edition, Crouse-Anglin, pp. 757-
763.
2. Measure/convert units from English to metric or vice
versa.

3. Apply correct procedures in checking tire pressure.

4. Call the instructor to check your performance.

Code No. Performing Underchassis Preventive Maintenance Date: Developed Date: Revised Page #
ALT723306
Oct. 26, 2003 May 24, 2004 80

INFORMATION SHEET LO6-1

Checking Tire and Tire Pressure

TIRES AND TUBES
Purpose of Tires
The automotive chassis includes the brake, steering, and
suspension systems. The chassis components that drive
the vehicle and support its weight are the wheels and tires.
Only the vehicle tires have contact with the road surface.
Tires have two functions. First they are airfilled cushions
that absorb most of the shocks caused by road
irregularities. The tires flex as they meet those
irregularities. This reduces the effect of road shocks on the
vehicle, passengers, and load. Second, the tires grip the
road to provide good traction. This enables the vehicle to
accelerate, brake and make turns without skidding.

Types of Tires
There are two types of ties: tube and tubeless. Tube tires
have an inner tube inside the tire. This is a round rubber
container that holds the air which supports the vehicle.
Both the tube and tire mount on the wheel rim. The tire
valve is part of the tube and protrudes through the rim.
Compressed air is forced through the valve to inflate the
tube. The air pressure in the tube then causes the tire to
hold its shape. Tubes are used in some truck and
motorcycle tires. Tubes are seldom used in passenger and
light-duty vehicles. Most automotive vehicles use tubeless
tires. The tire mounts on an airtight rim so air is retained
between the flange and the tire bead.

Code No. Performing Underchassis Preventive Maintenance Date: Developed Date: Revised Page #
ALT723306
Oct. 26, 2003 May 24, 2004 81

Tire Construction
The tire casings for tube and tubeless tires are
made in the same way. Layers of cord or plies are
shaped on a form and impregnated with rubber.
The tire sidewall and treads are then applied. They
are vulcanized in place to form the tire. To
vulcanize means to heat the rubber under pressure.
This molds the tire into desired form.
The number of cord layers or plies varies.
Passenger-car tires have 2, 4, or 6 plies. Heavy-
duty truck and bus tires may have up to 14 plies.
Tires for heavy-duty service, such as earth-moving
machinery, may have up to 32 plies.
All tires do not have the same shape or profile. The
aspect ratio or profile ratio differs. This is the ratio
of a tire's section height to section width. Three
aspect ratios are 80, 70, and 60. The lower the
number, the wider the tire appears. A 60-series tire
is only 60 percent high as it is wide.

Bias and Radial Plies
Plies can be applied two ways: diagonally or
radially. For many years, most tires had diagonal or
bias plies. These plies crisscross. This makes a tire
that is strong in all directions because the plies
overlaps, However, the plies tend to move against
each other and produce heat, especially at high
speed. Also, the tread tends to close or "squirm' as
it meets the road. Radial tires were brought out to
remedy these problems. In a radial tire, the plies
run parallel to each other and vertical to the tire
bead. Stabilizer belts are applied over the plies to
give strength parallel to the beads. Belts are made
of rayon, nylon, fiberglass, or steelmesh.

All new cars and most light-duty vehicles have
radial tires. The radial-tire sidewall is more flexible
than the bias-ply. Therefore, the radialtire tread
wraps around the edge of the tire to compensate
for the flexible sidewall. The result is that the radial
tread does not hell up as much when the vehicle
rounds a curve. This keeps more of the tread on
the road and reduces the tendency of the tire to
skid.

Code No. Performing Underchassis Preventive Maintenance Date: Developed Date: Revised Page #
ALT723306
Oct. 26, 2003 May 24, 2004 82

The radial tire provides better fuel economy than a bias-ply tire. This is because the radial has
less rolling resistance and less engine power is required to roll the tire. The radial also wears
more slowly. It has less heat buildup and the tread does not squirm as the tire meets the road.
Some bias-ply tires are belted. These tires are bias-ply tires to which stabilizer belts have been
added under the tread.

Tire Tread
Tire tread is part of the tire that meets the road. It
has a raised pattern molded into it. There are many
designs, depending on the intended use of the tire.
Many passenger vehicles use mud-and-snow tires.
These can be identified by M+S or M&S molded into
the sidewall. They provide quiet running with good
traction in mud and snow.

Mud and snow tires are used on four-wheel-drive pickup trucks. Its tread pattern is deeper and
wider or "more aggressive" than normal tread designs. This provides better mud-and-snow
traction with acceptable wear on paved surfaces. The tread compound is also designed to resist
tearing and chunking.
The treads shown are symmetric and nondirectional. "Nondirectional" means the tire can run
equally well in either direction. The tire can be installed with either sidewall facing out. The tire
must be installed for forward rotation in the direction of an arrow on the sidewall.

Directional and asymetric sports car tread are used as the rear of the Chevrolet Corvette.
"Asymetric" means the inside half of the tread is not the same as the outside half. The tire is
installed on the side of the car marked on the sidewall, and with the specified direction of
forward rotation. This tire provides better braking and handling characteristics than a
comparable symmetric, nondirectional tire. Different size tires are used at the front and rear of
the Corvette. As a result, each tire is position specific. It can run only in a specified wheel-
position on the car. Other tires are classified as snow tires, studded tires, and off-road tires.
Snow tires have large rubber cleats that cut through snow to improve traction. Studded tires
have steel studs that stick out above the tread. These improve traction on ice and snow.
However, many states regulate or ban studded tires because of possible damage to the road
surface. A variety of off-road tires are available. These often have tread patterns using knobs or
cleats. Off-road tires usually make noise and wear prematurely when driven on the highway.

Code No. Performing Underchassis Preventive Maintenance Date: Developed Date: Revised Page #
ALT723306
Oct. 26, 2003 May 24, 2004 83

Some tires use two different compounds in the tread. Con compound is softer than the other for
improved traction. In general, the softer the compound, the better the traction. The harder the
compound, the longer the tread life.

Tire Valve
Air is put into the tire or tube trough a spring-loaded tire valve or Schrader valve. On tube tires,
the valve is on the inner tube and sticks out through a hole in the rim. Tubeless tires use a
separate tire valve mounted in a hole in the rim.
Spring force and air pressure hold the tire valve in its normally-closed position. A cap is usually
threaded over the valve stem end to protect it from dirt. The cap also keeps guard against air
leaks. Some tire valves have a non-movable valve core. The core is three-pronged white
plastic. A special deflator is required to let air out of the tube.

Code No. Performing Underchassis Preventive Maintenance Date: Developed Date: Revised Page #
ALT723306
Oct. 26, 2003 May 24, 2004 84

Tire pressure
The amount of air pressure in the tire
depends on the type of tire and how it is
used. Passenger-car tires are inflated from
about 22 to 36 psi (152 to 248 kPa).
Heavyduty tires for trucks and buses may be
inflated to 100 psi (690 kPa). The maximum
inflation pressure is marked on the tire
sidewall. A tire placard or tire information
label lists the recommended inflation
pressure for each tire. This label is usually
located on a door edge or door jamb, or
inside the glovebox door. The label also lists
maximum load and tire size (including
spare). Running the tires at the specified
pressure helps provide better vehicle
handling while avoiding premature tire wear.
Underinflated tires wear on the outsides of
the tread.

Also, the tires flex excessively which
produces extra heat and more rapid wear.
Overinflation causes the center of the tread
to wear. The tire cannot flex normally and
this puts stress on the sidewalls and plies.

Tire Pressure Monitoring
Some vehicles have an electronic low-tire
pressure warning system (TPWS). This
system senses or monitors the tire pressure
in a moving vehicle. When the pressure
drops in a tire, an instrumentpanel light
illuminates to alert the driver. A tire-pressure-
sensor and transmitter mounts inside the
tires on each wheel. When the tire pressure
fall below 25 psi (172 kPa), the tire pressure
sensor sends a radio signal to the receiver-
control module in the instrument panel. This
turns on the
LOW TIRE PRESSURE light.
The receiver-control module also has
selfdiagnostic capabilities and can store fault
codes. If no signal is received from a
tirepressure sensor, the control module turns
on a SERVICE LTPWS light.

Code No. Performing Underchassis Preventive Maintenance Date: Developed Date: Revised Page #
ALT723306
Oct. 26, 2003 May 24, 2004 85

The tire-pressure sensors are peizoelectric devices and do not need batteries. In a piezoelectric
device, a small voltage appears across a crystal when a pressure is applied. In the tire-pressure
sensors, the vibration produced by the rolling tire generate the voltage. Therefore, the system
works only when the vehicle is moving or the tire is being vibrated.

Tire Size and Sidewall Markings
The format for the metric tire-size designation found on most tires is shown. Various letters and
numbers may appear in each position. Each marking has a special meaning.

TIRE INSPECTION
Cautions for Servicing Tires
Several cautions must be followed to avoid personal injury and to prevent damage to the wheel
and tire.
1. Matching tire and wheel width. Do not try to

install a narrow tire with a high-aspect ratio on
a wide rim. For example, a tire with an 80
aspect ratio must not be installed on a wide rim
that requires a 60 tire.

2. Matching tire and wheel diameter. Do not try to
mount a 16-inch tire on a 16.5-inch wheel, or a
15-inch tire on a 15.5-inch wheel. The result
could be a deadly explosion when inflating the
tire. Check the rim size. It may be stamped
near the center of the wheel disc.

3. Mixing tires. All tires on a vehicle should be the
same size, construction (radial or non-radial),
and speed rating unless otherwise specified by
the vehicle manufacturer. If two radials and two non-radials are on the vehicle, put the
radials on the rear. Snow tires should be installed in pairs on the drive axle (either front or
rear), or on all four wheels. Never put non-radial (bias or belted-bias) snow tires on the rear
if radials are on the front. Match tire sizes and construction on four-wheel drive vehicles.
Tires affect vehicle stability and handling. Mixing tires may cause handling problems.

4. Respecting compressed air. A terrific force is contained in an inflated tire. An explosion of
the tire-and-wheel assembly can result from improper or careless mounting procedures.
Never stand over a tire while inflating it. If the tire explodes, the sudden release of
compressed air has enough energy to throw a person more than 30 feet (9 m) in the air.
People have been seriously injured or killed by exploding tires.

5. Protecting your eyes Wear eye protection (safety glasses, safety goggles, or a face shield)
when demounting and mounting tires. When deflating a tire, avoid the air stream from the
tire valve. The air comes out at high speed and can blow dirt or debris into your eyes.

Code No. Performing Underchassis Preventive Maintenance Date: Developed Date: Revised Page #
ALT723306
Oct. 26, 2003 May 24, 2004 86

Checking Tire Pressure and Inflating Tires
Before checking tire pressure and adding air, know the correct pressure for the tire. The
specification is in the owners manual and on the vehicle tire-information label. When the vehicle
is carrying a heavy load, pulling a trailer, or driving at sustained highway speed, higher tire
pressure may be necessary. Maximum pressure should never exceed the maximum pressure
marked on the tire sidewall.
Inflation pressure is given for a cold tire. Pressure increases as tire temperature rises. Highway
driving on a hot day can increase the tire pressure from 5 to 7 psi (35 to 48 kPa). As the tire
cools, it loses pressure. Never bleed a hot tire to reduce its pressure. The pressure will then be
low when the tire cools. Install the cap on the tire valve after checking pressure or adding air.

Tire Inspection
The purpose of inspecting tires is to determine if they are safe for further use. When defects or
improper wear patterns are found, inform the driver. Recommend the services that will correct
the cause of the abnormal wear.
Tires have tread-wear indicators or wear bars. These are filled-in sections of the tread grooves
that will show when the tread has worn down to 1/16 inch (1.6 mm). A tire with a wear bar
showing is worn out and should be replaced. Too little tread remains for continued safe driving.
A tread-depth gauge can be inserted into the tread grooves to measure tread depth of at least
1/32 inch (0.8 mm) in any two adjacent grooves at any location on the tire.
Check for bulges in the sidewalls. Bulges mean plies have separated and the tire could fail at
any time. Tires with separated or broken plies should be replaced.

Code No. Performing Underchassis Preventive Maintenance Date: Developed Date: Revised Page #
ALT723306
Oct. 26, 2003 May 24, 2004 87

SELF-CHECK LO6-1

1. Technician A says the lower the aspect ratio the wider the tire appears. Technician B says
aspect ratio is the ratio of the tires section height to section width. Who is right?
a. A only
b. B only
c. both A and B
d. d. neither A nor B

2. All the following are true about radial tires except-
a. all plies run parallel to each other
b. there is less squirm than with bias-ply tires
c. a belt steel mesh or other material is applied over the plies
d. a radial tire has greater rolling resistance than bias plies

3. Recommend inflation pressures for the front and rear tires on the car are listed in the-
a. VECI label
b. tire information label
c. VIN number
d. sidewall markings

4. If two radials and two non-radials are on the vehicle, the radials should be-
a. on the front c. removed from the vehicle
b. on the rear d. inflated to a higher pressure

5. When rotating tires, all the following are true except-
a. do not rotate tire if the front and rear tires are of different sizes.
b. directional tires must remain on the same side of the car.
c. check tire pressure after rotating tires.
d. always perform a five tire rotation.

Code No. Performing Underchassis Preventive Maintenance Date: Developed Date: Revised Page #
ALT723306
Oct. 26, 2003 May 24, 2004 88

ANSWER KEY LO6-1

1. A
2. D
3. B
4. B
5. A

Code No. Performing Underchassis Preventive Maintenance Date: Developed Date: Revised Page #
ALT723306
Oct. 26, 2003 May 24, 2004 89

Qualification Automotive Servicing NCI
Module Title Performing Underchasis Preventive Maintenance

Learning Outcome # 7 Check underchasis body bolts and nuts

Assessment Criteria : 1. Body bolts and nuts inspected for tightness and damage.
2. Cross member bolts and nuts checked for tightness.
3. Transmission mounting bolts and nuts checked.
4. Propeller shaft bolts and nuts checked for tightness and

damage.
5. Leaf spring shackle center bolts and nuts checked for

tightness and damage.

Resources :

1. Automotive Mechanics 10th ed; Crouse- pp. 58-69
Anglin; pp. 38-47

2. Power train and under chassis. (Shop pp. 11-17
manual)

Code No. Performing Underchassis Preventive Maintenance Date: Developed Date: Revised Page #
ALT723306
Oct. 26, 2003 May 24, 2004 90

LEARNING EXPERIENCES
Learning Outcome #7: Check underchassis body bolts and nuts

Learning Activity #1 Resources

This is your last activity for Module 1. Automotive Mechanics 10th
In this activity, you are going to: edition, Crouse and Anglin, pp.
1. Read: Resource to identify the location of 38-47.

underchassis bolts and nuts.

2. Indicate your observation in the diagram provided.

3. Check underchassis body bolts and nuts for tightness Fill-out the checklist.
and damage.

4. Self Check #9

5. Refer to Model Answers #9

6. Call the instructor to check your work.

Code No. Performing Underchassis Preventive Maintenance Date: Developed Date: Revised Page #
ALT723306
Oct. 26, 2003 May 24, 2004 91

INFORMATION SHEET LO7-1

Checking Underchassis Body Bolts and Nuts

Fasteners
Fasteners hold automotive parts together,
Examples are screws, nuts, and studs. Others
are rivets, snap rings, and cotter pins. Most
fasteners are removable so the assembly can
be taken apart. There are 3 permanent ways
of fastening pans together, such as soldering
and welding. Metal pans and panels are
welded together to form the car body.

Screw Threads
A fastener that has a spiral ridge, or screw
thread, on its surface is a threaded fastener.
This includes bolts, screws, studs, and nuts.

Bolts and screws are lengths of rod with a
head on one end and threads on the other. A
stud looks like a headless bolt with threads on
one or both ends. Bolts, screws. And studs
have external (outside) threads, Nuts and
threaded (or tapped) holes have internal
(inside) threads.
Screws, bolts, studs, nuts, and tapped
(threaded) holes are manufactured with either
US customary (USC) or metric screw threads.
They are not interchangeable. A USC screw
will not fit a metric tapped hole.
And a metric screw will not fit a USC tapped
hole. Some cars have metric fasteners.
Others have USC fasteners. Some have both.
To work on a variety of cars, you need new
fasteners of both types available. In addition,
your tools must include both USC and metric
sockets and wrenches.

USC Screw Threads
Five ways of describing USC screw threads
are:
1. By size
2. By threads per inch or pitch
3. By thread series, which is the coarseness

or fineness of the thread
4. By thread class (closeness of fit)
5. By right-hand or left-hand direction of the

threads. All threads are right-hand unless otherwise noted. If the bolt tightens as the head is
turned clockwise, the bolt has right-hand threads.

When you are doing a service job, you must use the correct screw, bolt, or nut. A 1/4-inch
screw can have 20, 28, or 32 threads per inch. You cannot use a 20-thread (coarse) screw in a
28-thread (fine) hole.

Code No. Performing Underchassis Preventive Maintenance Date: Developed Date: Revised Page #
ALT723306
Oct. 26, 2003 May 24, 2004 92

METRIC SCREW THREADS
Metric bolts, screws, and threads are measured in millimeters. Thread pitch is the distance
between individual threads. A pitch may run from 1 to 2 mm as the diameter of the threads
increases. A bolt with a basic thread diameter of 6 mm has a pitch of 1 mm. A bolt with a thread
diameter of 16 mm has a pitch of 1 mm.

Bolt and Screw Strength
The type of material from which the bolt or screw is made determines its strength. Markings on
USC and metric screw and bolt heads show their strength. Common metric fastener bolt-
strength markings are 9.8 and 10.9. On metric fasteners, the higher number indicates greater
strength.

The table shows typical applications for bolts or screws of
different strength. The minimum tensile strength is the pull in
pounds that a round rod with a cross section of 1 square inch can
stand before it break apart. Higher-strength bolts and screws are
more expensive. They are used only where the
added strength is needed.
Screw and Bolt Heads
Vehicles have a great variety of screw and bolt heads. Several
parts along with screwdrivers and wrenches required to turn them
are shown. Most bolts have hex heads. This means the heads are
hexagonal, or six-sided.

Nuts
The hex nut is the most common in the automotive shop. The
slotted hex and the castle nut are used with a cotter pin.

Code No. Performing Underchassis Preventive Maintenance Date: Developed Date: Revised Page #
ALT723306
Oct. 26, 2003 May 24, 2004 93

Code No. Performing Underchassis Preventive Maintenance Date: Developed Date: Revised Page #
ALT723306
Oct. 26, 2003 May 24, 2004 94

Code No. Performing Underchassis Preventive Maintenance Date: Developed Date: Revised Page #
ALT723306
Oct. 26, 2003 May 24, 2004 95

Code No. Performing Underchassis Preventive Maintenance Date: Developed Date: Revised Page #
ALT723306
Oct. 26, 2003 May 24, 2004 96

SELF-CHECK LO7-1

Select the one correct, best, or most probable answer to each question. You can find the
answer in the section indicated at the end of each question.

1. Pitch in USC threads is:
a. distance between individual threads
b. number of threads per inch
c. depth of the threads
d. thread class

2. Pitch in metric threads is the:
a. thread class
b. number of threads per inch
c. depth of the threads
d. distance between individual threads

3. Technician A says the more lines there are on the head of a USC bolt, the stronger the
bolt. Technician B says the higher the number of the head of a metric bolt, the stronger
the bolt. Who is right?
a. A only
b. B only
c. both A and B
d. neither A nor B

4. Nuts and bolts that have a continuous resistance turning are:
a. prevailing-torque fasteners
b. torque-to-yield fasteners
c. used with a cotter pin
d. self-tapping setscrews

5. Bolts that are tightened by measuring how much head is turned are:
a. prevailing-torque fasteners
b. torque-to-yield fasteners
c. used with a cotter pin
d. self-tapping setscrews

6. Before installing a bolt in an aluminum part, coat bolt threads with antiseize compound
to:
a. lock the bolt in place
b. prevent thread damage when removing the bolt
c. turn the bolt with less torque
d. none of the above

Code No. Performing Underchassis Preventive Maintenance Date: Developed Date: Revised Page #
ALT723306
Oct. 26, 2003 May 24, 2004 97

ANSWER KEY LO7-1

1. B
2. D
3. B
4. A
5. B
6. A

Code No. Performing Underchassis Preventive Maintenance Date: Developed Date: Revised Page #
ALT723306
Oct. 26, 2003 May 24, 2004 98

PERFORMANCE TEST

Learner's Name Date
Competency: Perform Underchassis Preventive Maintenance
Test Attempt
1st 2nd 3rd

Directions: OVERALL EVALUATION

CALL INSTRUCTOR and ask Level PERFORMANCE LEVELS
him/her to assess your Achieved
performance in the following critical 4 – Can perform this skill without supervision and
task and performance criteria with initiative and adaptability to problem situations.
indicated below 3 – Can perform this skill satisfactorily without
assistance or supervision.
You will be rated based on the 2 – Can perform this skill satisfactorily but requires
overall evaluation outlined on the some assistance and/or supervision.
right side. 1 – Can perform parts of this skill satisfactorily, but
requires considerable assistance and/or supervision.

Instructor will initial level achieved.

PERFORMANCE STANDARDS Yes No N/A
For acceptable achievement, all items should receive a "Yes" or
"N/A" response.
• Clutch fluid must be between the minimum and the maximum levels.
• No twisted or bent clutch lines.
• Clutch cover must be fitted in the cap.
• Clutch fluid must be clear and not diluted with other substances.
• Gear oil must be in accordance with manufacturer specifications.
• The vehicle must be on flat surface.
• Transmission gear oil must be clear and not diluted with other

substances.
• Grade/classification and level of gear oil must be in accordance with

manufacturer specifications.
• No leakage in the power steering linkage and connections.

• The vehicle must be parked and engine running at idle speed.

• Inspection/replacement and level of fluid must be in accordance with
manufacturer's specifications.

• Checking and refilling of automatic transmission fluid (ATF) must be in
accordance with manufacturer's specifications.

• Air tank must be free of water, moisture and other foreign materials.

• Tires no damage or deformities and no solid object struck on it.

• Tire pressure must be in accordance with manufacturer's
specifications.

• Bolts/nuts including tire stud bolts/nuts are accurately determined.

• Body bolts/nuts torque is within the manufacturer's specifications.

• Checking procedure according to manufacturer's specifications.

• Tightness of the bolts is determined by the sound produced by tapping
lightly bolts/nuts with pointed hammer.

Code No. Performing Underchassis Preventive Maintenance Date: Developed Date: Revised Page #
ALT723306
Oct. 26, 2003 May 24, 2004 99