B
98
Repair and Service Manual
MECHANICAL BRAKES
Read all of SAFETY and this section before attempting any procedure. Pay particular attention to Notices, Cautions, Warnings and Dangers.
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3.
Observe the vehicle stopping location or measure
the vehicle stopping distance from the point at which
the brakes were latched. The vehicle should stop
within the “normal” range of stopping distances.
4.
If the vehicle stops more than 4 ft. (1.2 m) beyond
the acceptable stopping distance or pulls to one side,
the vehicle has failed the test.
5.
Repeat the test two more times.
6.
If the vehicle fails to pass two of three Periodic Brake
Performance Tests, perform the Aggressive Stop
Test 10 times, then repeat the Periodic Brake Perfor-
mance Test three more times (second set of three).
7.
If the vehicle passes two of three Periodic Brake Per-
formance Tests, check that the clevis pins at the
brake levers are loose. If they are loose, return the
vehicle to service. If they are tight, adjust the brake
pedal free travel (See Adjusting Brake Pedal Free
Travel on page 101).
8.
Repeat the Periodic Brake Performance Tests.
9.
If vehicle fails, remove it from service and inspect the
wheel brake assembly to evaluate the reason for fail-
ure (See Wheel Brake Inspection on page 98).
Aggressive Stop Test
To prevent a serious injury or death,
all brake tests must be done in a
safe location with regard for the
safety of all personnel.
Always conduct a visual inspection and evaluate
pedal travel before operating a vehicle to verify some
braking function is present.
The purpose of this test is to attempt to fully expand and
release the brake adjusters on a vehicle which has failed
the first set of Periodic Brake Performance Tests. It is
important that the technician/mechanic exercise care
and perform the test in a non-congested area with
regard for the safety of all personnel.
1.
Equally load both sides of the vehicle (Ref Fig. 13)
and apply maximum force and travel to the service
brake pedal while moving.
2.
Do not latch the parking brake.
3.
Do this a total of 10 times with the first few at slow
speed.
4.
If brake function is adequate or improves, increase
speed for the remaining tests.
5.
Before the end of the tests, both wheels should lock
at approximately the same time and slide straight.
NOTICE: The brake adjuster mechanism must
expand and release fully to function. Under light
usage this may not occur, even though the vehicle
stops acceptably.
The adjuster functions most consistently with aggressive
braking.
Fig. 13 Equally Load Vehicle
Wheel Brake Inspection
Wear a dust mask and eye protection
whenever working the on wheel
brakes. Do not use pressurized air to
blow dust from the brake assemblies. Replace both
brake shoes on both wheels if one or more shoes are
worn below .06” (1.5mm) thickness at any point.
Do NOT touch any of the wheel
brake mechanism except as
instructed.
Do NOT use a commercial brake cleaner unless the
entire brake has been disassembled.
1.
Remove the brake drums. Do not disturb the
adjuster mechanisms (See Brake Drum Removal
and Installation on page 102).
2.
Remove any excess dust and dirt from the drum with
a brush.
The drum must not be turned to
“true” a worn friction surface.
Turning will make the drum too thin
and will cause drum failure and a loss of brakes
which could cause severe injury or death.
3.
Inspect the brake drum.
•
Look for a blue coloration or blistered paint that
would indicate that it has overheated.
•
Check for any evidence of scoring.
•
Check for any excessive wear indicated by the
friction surface being significantly worn and
leaving a ledge of unworn drum.
•
Inspect the splines for galling, wear, and corro-
sion.
•
If any of these problems are found, the drum
must be replaced.
4.
Remove any accumulated brake dust from the wheel
brake assembly with a brush.
5.
Visually inspect the axle seal for oil leakage and the
condition of the thrust washer. If oil is present, a
repair to the rear axle is necessary (See Axle Shaft,
Bearing and Seal Removal on page 112).
PRELIMINARY
