GMC 4000 Series Service Manual page 207

Sec. 5A
Page 200
HYDRAULIC BRAKES
LOW PEDAL OR PEDAL GOES TO TOE BOARD
PROBABLE CAUSE
1
. E xcessive clearance between linings and drum.
2. Automatic adjusters not working.
3. Weak brake hose.
4. Leaking conduits.
5. Leaking wheel cylinder.
6. Leaking master cylinder.
7. Leaking master cylinder check valve.
8. Air in system .
9. Plugged master cylinder filler cap.
10. Improper brake fluid.
11. Low fluid level.
SPRINGY, SPONGY PEDAL
PROBABLE CAUSE
1.
Air trapped in hydraulic system.
2. Improper brake fluid.
3. Improper lining thickness or location.
4. Drums worn too thin.
5. Master cylinder filler vent clogged.
6. Weak hose.
EXCESSIVE PEDAL PRESSURE REQUIRED TO STOP
PROBABLE CAUSE
1
Brake adjustment not correct.
.
2. Incorrect lining.
3. Grease or fluid soaked lining.
4. Lining not in full contact.
5. Improper fluid.
6. Frozen master or wheel cylinder pistons.
7. Brake pedal binding on shaft.
8. Linings installed on wrong shoes.
9. Glazed linings.
10. Bellmouthed, barrel-shaped or scored drums.
G M C S E R V I C E M A N U A L
TROUBLESHOOTING CHART
1
Adjust brakes.
.
2. Make forward and reverse stops; if pedal stays
low, repair faulty adjusters.
3. Replace with new hose.
4. Repair or replace faulty parts.
5. Clean and rebuild.
6. Clean and rebuild.
7. Install new check valve.
8. Bleed system.
9. Clean filler cap vent holes; bleed system .
10. Flush system and refill with recommended
brake fluid.
11. F ill reservoir with brake fluid; bleed system .
1.
Remove air by bleeding.
2. Flush, refill and bleed system . Use recom ­
3. Install specified lining or replace shoe and
4. Replace drums.
5. Clean vent or replace cap; bleed brakes.
6. Install new hose.
1
.
2. Install specified linings.
3. Repair grease seal or wheel cylinder. Install
4. Grind lining to proper radius.
5. Flush out system; fill with recommended fluid;
6. Recondition or replace all cylinders.
7. Lubricate.
8. Install primary and secondary linings
9. Sand surface of linings.
10. Replace or resurface drums in R.H. and L.H.
REMEDY
REMEDY
mended brake fluid.
lining.
REMEDY
Adjust the brakes.
new linings.
bleed.
correctly.
pairs.