5-4 BRAKES
DIAGNOSIS
ROAD TESTING BRAKES
Brakes should be tested on dry, clean, smooth and
reasonably level roadway which is not crowned. Road
test brakes by making brake applications with both
light and heavy pedal forces at various speeds to de-
termine if the vehicle stops evenly and effectively.
Also drive vehicle to see if it leads to one side or the
other without brake application. If it does, check the
tire pressure, front end alignment and front suspen-
sion attachments for looseness. See diagnosis table
for other causes.
BRAKE FLUID LEAKS
Check the master cylinder fluid levels. While a slight
drop in reservoir level does result from normal lining
wear, an abnormally low level indicates a leak in the
system. In such a case, check the entire brake system
for leakage. If even a slight evidence of leakage is
noted, the cause should be corrected or defective
parts should be replaced.
SUBSTANDARD OR CONTAMINATED BRAKE
FLUID
Improper brake fluid, mineral oil or water in the fluid
may cause brake fluid to boil or rubber components
in the hydraulic system to deteriorate.
If primary piston cups are swollen, then rubber parts
have deteriorated. This deterioration may also be evi-
denced by swollen wheel cylinder piston cups on the
drum brake wheels.
If deterioration of rubber is evident, disassemble all
hydraulic parts and wash with alcohol. Dry these parts
with compressed air before assembly to keep alcohol
out of the system. Replace all rubber parts in the sys-
tem, including hoses. Also, when working on the
brake mechanisms, check for fluid on the linings. If ex-
cessive fluid is found, replace the pads or linings.
If master cylinder piston seals are satisfactory, check
for leakage or excessive heat conditions. If leakage
is not found, drain fluid, flush with brake fluid, refill and
bleed system.
The system must be flushed if there is any doubt as
to the grade of fluid in the system or if fluid has been
used which contained parts that have been subjected
to contaminated fluid.
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