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8-8
TROUBLE DIAGNOSIS
SECTION 8-B
BRAKE TROUBLE DIAGNOSIS
CONTENTS OF SECTION 8-B
BRAKES
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8-5
Testing Brakes
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8-8
8-6
External Conditions that Affect
Brake Performance.
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8-8
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8-7
Brake Trouble Indications and
Corrections
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8-8
Bulletin
No.
Page No.
SERVICE BULLETIN REFERENCE
SUBJECT
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8-5 TESTING BRAKES
Brakes must be tested on dry, clean, reason-
ably smooth and level
roadway.
A true test of
brake performance cannot be made if roadway
is wet or greasy, or is covered with loose dirt
so that all tires do not grip road equally. A
true test cannot be made if roadway is crowned
so as to throw weight of car toward wheels on
one side, or is so rough that wheels tend to
bounce.
Test brakes at different car speeds with both
light and heavy pedal pressure; however, avoid
locking the wheels and sliding th
e
tires on road-
wa.y. This practice is injurious to tires and it
does not give a true test of brake performance.
Overall brake performance cannot be fully
tested with
the
wheels jacked up. Applying
brakes by foot pressure or pedal jack while
testing brake drag by hand or with a torque
measuring device will aid in getting an equal
adjustment at all brake shoes, and should be
used during brake adjustment. This procedure,
however,
does not test the
self-energizing
ac-
tion as the primary shoes come in contact with
drums, nor the braking action as car weight is
transferred forward on deceleration.
8-6 EXTERNAL CONDITIONS THAT
AFFECT BRAKE PERFORMANCE
In addition to roadway conditions mentioned
in the previous paragraph, the following exter-
nal conditions may affect brake performance
and should be corrected before work is done on
the brake mechanism.
a. Tires. All tires must be inflated to equal
pressure before testing brakes. Tires should be
the same size and of approximately equal tread
condition.
One or more smooth tires combined
with tires having good tread patterns will cause
an erroneous impression of brake
performance.
b. Car Loading. Unusual or unequal loading
of the car will affect brake
performance
and
must be taken into consideration when judging
the condition of brakes.
c. Front End
Alignment.
Misalignment of
the front end, particularly in regard to limits
on camber and king pin inclination, will cause
brake action to appear unequal between sides
d. Shock Absorbers.
If
shock absorbers are
not functioning properly
they
may permit
bouncing of car on quick stops and give the er-
roneous impression that brakes are too severe.
8-7 BRAKE TROUBLE INDICATIONS
AND CORRECTIONS
a. Brake Pedal Goes to Toeboard
(1)
E
xcessive Brak e
Sho
e Clearance.
Exces-
sive
clearance
is indicat ed if a good brake is
obtained
after
pumping brake pedal several
times. Condition may be caused by wear of
brake linings or by a loose initial adjustment
of shoes. Adjust brakes (par. 8-12)
.
(2) Fluid Reservoir Empty.
If
fluid reser-
voir is empty, a good brake cannot be obtained
by pumping brake pedal. Fill reservoir (par.
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