Brake System Maintenance; Brake Adjustments - GMC 4000 Series Service Manual

Sec. 5A
Page 162
HYDRAULIC BRAKES
Figure I — Typical Vacuum and Hydraulic Lines Installed (Remote M ounted Booster)
inders, lines, gauges, reserve tanks, etc., are
covered under respective headings in this section.
For illustration of typical system installation
see figure 1.

BRAKE SYSTEM MAINTENANCE

1. Maintain proper level of hydraulic brake
fluid in master cylinder. Refer to LUBRICATION
(SEC. 0) for recommended fluid and checking in­
tervals. At least once a year, drain and flush en­
tire brake system and refill with new fluid.
2. Adjust brake shoes at regular intervals.
After two or three adjustments, check brake linings
for wear. Reline brakes before lining is worn suf­
ficiently to permit lining rivets to damage brake
drums.
3. Keep brake pedal and linkage well lubri­
cated to assure free movement and rapid release
of brakes.
4. Inspect entire brake system regularly for
fluid leakage. Leakage must be corrected immed­
iately.
5. Make sure brake shoes are free on their
mountings, that shoe return springs are not weak
or broken, and that backing plates are not sprung
or loose on axle or steering knuckle.
G M C S E R V I C E M A N U A L
cylinder air cleaner, referring to LUBRICATION
(SEC. 0) for recommended intervals and for serv ­
ice instructions. Air cleaners on dash mounted
booster and master cylinder assembly are integral
part of complete assembly and can be serviced
only when assembly is removed from the vehicle
as part of unit overhaul.
fittings and connections.
directed later under "Power Cylinders." These
tests may reveal sub-standard performance before
the condition becomes bad enough to cause driver
complaints or brake failure on the road.
these vehicles:
Air Cleaner
Vacuum Gauge
Master Cylinder
Vacuum Line From Engine
(From Vacuum Pump on D iesel)
Brake Pedal
Vacuum Power Cylinder
Vacuum Line From Engine
to Control Valve
Hydraulic Line From
Master Cylinder
Hydraulic Line to Wheels
10 Atmosphere Line From
Air Cleaner
6. Service remote mounted vacuum power
7. Tighten all vacuum and atmosphere line
8. Perform "Power Brake System Tests" as

BRAKE ADJUSTMENTS

There are six different type brakes used on
1. Type "F" manual adjusting - FRONT.
2. Type "FA" automatic adjusting - FRONT.
3. Type "FR-3" manual adjusting - REAR.
4. Type "FR-3A" automatic adjusting - REAR.
5. Duo-Servo automatic adjusting - FRONT.
6. Twin-Action automatic adjusting - REAR.