GMC 4000 Series Service Manual page 260

SERVICE BRAKES INOPERATIVE
PROBABLE CAUSE
1. Low air pressure
2. Faulty brake chamber diaphragm
3. Improper brake shoe adjustment
4. Improper wedge adjustment
5. Plunger seal failure
. Grease on linings
6
G M C S E R V I C E M A N U A L
. Check system for leaks
1
. Replace diaphragm
2
3. Adjust brake shoes
4. Make wedge adjustment
5. Replace seal and clean and lubricate actuation
. Reline brakes and check seals
6
REMEDY
parts
Sec. 5B
Page 253
AIR BRAKES