B
74
Repair and Service Manual
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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A subtle loss of performance may take place over time;
therefore, it is important to establish the standard with a
new vehicle.
Drive the vehicle at maximum speed on a flat, dry, clean,
paved surface (Ref. Fig. 15).
Quickly press the brake pedal to latch the park brake at
the line or marker in the test area and remove foot from
pedal. The vehicle should stop aggressively. The wheel
brakes may or may not lock.
Observe the vehicle stopping location or measure the
vehicle stopping distance from point at which the brakes
were latched. The vehicle should stop within the “normal”
range of stopping distances. If the vehicle stops more
than 4 ft. (1.2 m) beyond the acceptable stopping dis-
tance or pulls to one side, the vehicle has failed the test.
Repeat test two more times.
If vehicle fails to pass two of three Periodic Brake Perfor-
mance Tests, perform the Aggressive Stop Test 10 times
as described below. Then repeat the Periodic Brake Per-
formance Test three more times (second set of three).
If the vehicle passes two of three Periodic Brake Perfor-
mance Tests, check that the clevis pins at the brake
levers are loose. If they are loose, return vehicle to ser-
vice. If they are tight, adjust free travel. See “Adjusting
Brake Pedal Free Travel” on page 77. Then, repeat the Peri-
odic Brake Performance Tests. If vehicle fails, remove
from service and refer to ‘Wheel Brake Inspection’, to
evaluate the reason for failure.
Aggressive Stop Test
To prevent 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 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 use care and per-
form the test in a non-congested area with regard for the
safety of all personnel.
To perform an Aggressive Stop Test, equally load both
sides of the vehicle (Ref. Fig. 16) and apply maximum
force and travel to the service brake pedal while moving.
Do not latch the park brake.
Do this a total of 10 times with the first few at slow speed.
If brake function is adequate or improves, increase speed
for the remaining tests. Before the end of the tests, both
wheels should lock at approximately the same time and
slide straight.
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. 16 Evenly Loaded Vehicle
Wheel Brake Inspection
Wear a dust mask and eye protection working
on wheel brakes.
Do not use pressurized air to blow dust from
brake assemblies.
Replace both brake shoes on both wheels if
one or more shoes are worn below .06” (1.5
mm) 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 adjuster mechanisms. Remove
excess dust and dirt from the drum with a brush.
