Chevrolet 70 1969 Series, Shop Manual

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BRAKES 5A - 23
BRAKES C H A T T E R
PROBABLE C A U SE R E M E D Y
1. Incorrect lining to drum clearance.
1. Readjust to recommended clearances.
2. Loose backing plate.
2. Tighten securely.
3. Grease, fluid, road dust on lining.
3. Clean or reline.
4. W eak or broken retractor spring.
4. Replace.
5. Loose wheel bearings.
5 .
Readjust.
6 . Drums out-of-round.
6 . Grind or turn drums in pairs.
7. Cocked or distorted shoes.
7. Straighten or replace.
8 . Tapered or barrel-shaped drums.
8 . Grind or turn in pairs.
S H O E C L IC K
R E M E D Y
PROBABLE C A U S E
1. Shoes lift off backing plate and snap back.
. . .
1. Change drums side to side or grind drums
(in pairs).
2. Hold down springs weak.
2. Replace springs.
3. Shoe bent.
3. Straighten.
4. Grooves in backing plate pads.
4. Grind and lubricate.
T R O U B L E S H O O T IN G P O W E R H Y D R A U L IC BR AKES (Vacuum Assist Units)
N O T E : The same types of brake troubles are encountered with power brakes as
with standard brakes. Before checking the power brake system for
source of trouble, refer to trouble diagnosis of standard hydraulic brakes.
After these possible causes have been eliminated, check for cause as
outlined below.
N O T E : Make the following test before checking hard pedal for the cause. With
the engine stopped, depress the brake pedal several times to eliminate
all vacuum from the system. Apply the brakes, and while holding the foot
pressure on the brake pedal, start the engine. If the unit is operating
correctly, the brake pedal will move forward when the engine vacuum
power is added to the pedal pressure. If this test shows that the power
unit is not operating, the trouble may be one of the following:
B R A KE S Y S T E M L O S E S F L U ID
__________________ PROBABLE C A U SE______________________________________________ R E M E D Y _______________________
1. External Leak: Leaking-pipe connections, hose, 1. Clean parts. Replace defective parts. Tighten,
wheel cylinders, master cylinder head nut, etc.
2. Internal Leaks: Past secondary seals into 2. Rebuild master cylinder,
power unit. Check vacuum hose for fluid.
N O BOOST — H A R D P E D A L
PROBABLE CAUSE
R E M E D Y
1. Bent, broken obstructed tufre. Collapsed hose.
2. Stuck check valve.
1. Replace defective parts.
2. Replace valve.
CHEVROLET S E R ES 70 -80 H EAVY DUTY TRUCK SH O P M ANUAL