CONDITION POSSIBLE CAUSES CORRECTION
PEDAL IS SPONGY 1. Air in brake lines. 1. Bleed brakes.
2. Power brake booster runout
(vacuum assist).
2. Check booster vacuum hose and
engine tune for adequate vacuum
supply. Refer to power brake booster in
the diagnosis and testing section.
PREMATURE REAR
WHEEL LOCKUP
1. Contaminated brake shoe linings. 1. Inspect and clean, or replace shoes.
Repair source of contamination.
2. Inoperative proportioning valve. 2. Test proportioning valves folowing
procedure listed in diagnosis and
testing section. Replace valves as
necessary.
3. Improper power brake booster
assist.
3. Refer to power brake booster in the
diagnosis and testing section.
STOP LAMPS STAY ON 1. Brake lamp switch out of
adjustment.
1. Adjust brake lamp switch.
2. Brake pedal binding. 2. Inspect and replace as necessary.
3. Obstruction in pedal linkage. 3. Remove obstruction.
4. Power Brake Booster not allowing
pedal to return completely.
4. Replace power brake booster.
VEHICLE PULLS TO
RIGHT OR LEFT ON
BRAKING
1. Frozen brake caliper piston. 1. Replace frozen piston or caliper.
Bleed brakes.
2. Contaminated brake shoe lining. 2. Inspect and clean, or replace shoes.
Repair source of contamination.
3. Pinched brake lines. 3. Replace pinched line.
4. Leaking piston seal. 4. Replace piston seal or brake caliper.
5. Suspension problem. 5. Refer to the Suspension group.
PARKING BRAKE -
EXCESSIVE LEVER
TRAVEL
1. Rear parking brake shoes out of
adjustment.
1. Adjust rear parking brake shoes.
POWER BRAKE BOOSTER
BASIC TEST
(1) With engine off, depress and release the brake
pedal several times to purge all vacuum from the
power brake booster.
(2) Depress and hold the pedal with light effort (15
to 25 lbs. pressure), then start the engine.
The pedal should fall slightly, then hold. Less effort
should be needed to apply the pedal at this time. If
the pedal fell as indicated, perform the VACUUM
LEAK TEST listed after the BASIC TEST. If the
pedal did not fall, continue on with this BASIC
TEST.
(3) Disconnect the vacuum hose on the side of the
vacuum check valve that leads to the speed control,
then connect a vacuum gauge to the open vacuum
port on the valve.
(4) Start the engine.
(5) When the engine is at warm operating temper-
ature, allow it to idle and check the vacuum at the
gauge.
If the vacuum supply is 12 inches Hg (40.5 kPa) or
more, the power brake booster is defective and must
be replaced. If the vacuum supply is below 12 inches,
continue on with this BASIC TEST.
(6) Shut off the engine.
(7) Connect the vacuum gauge to the vacuum ref-
erence port on the engine intake manifold.
(8) Start the engine and observe the vacuum
gauge.
If the vacuum is still low, check the engine tune
and repair as necessary. If the vacuum is above 12
LH BRAKES 5 - 13
DIAGNOSIS AND TESTING (Continued)
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