GMC 4000 Series Service Manual page 218

1 Line to Air Gauge
2 Valve Mounting Bolt
and Nut (in Engine
Compartment)
3 Lines to Trailer
Brakes Hand Control
Valve
9 Application
Valve Assembly
Figure 4 —Brake Pedal and Application Valve
lnstalled(Conv. Cab) (Typical)
3. Turn stop screw down until all free play is
removed; then back screw out l / 2 turn and lock.
4. Hold stop screw while tightening lock nut.
5. Check brake operation for full application
and release.
PEDAL STOP SCREW ADJUSTMENT
(CONVENTIONAL MODELS - Fig. 4)
On all conventional models, both Midland-Ross
and Bendix-Westinghouse application valves (pedal
assembly included) are used. Midland-Ross has a
stop screw and Bendix-Westinghouse has a stop
button as part of the assem bly. This stop screw,
or button, is used to adjust pedal to provide proper
pedal travel. If travel is too great, application will
be too slow and full application may not be obtained.
If travel is not great enough, brakes may not re­
lease completely. Adjust stop screw (button) as
follows:
1. Loosen lock nut.
2. Turn stop screw (M-R) into pedal bracket
until pedal roller does not touch exposed end of
G M C S E R V I C E M A N U A L
4 Double Check Valve
and Stop Light Switch
5 Line to Tractor
Protection Valve
6 Pedal Stop Button
7 Pedal Assembly
8 Pedal to Valve Bolts
T-2126
Figure 5 —Brake P edal Stop Installed ( " S " Models)
valve piston; or (B-W) until plunger does not touch
valve piston.
3. Turn stop screw (M-R) out of pedal bracket
until roller JUST TOUCHES exposed end of valve
piston; or (B-W) until plunger JUST TOUCHES
valve piston. In other words, there should be NO
FREE PLAY between pedal and valve piston.
4. Tighten lock nut without moving stop screw
(or button).
5. Check brake operation for full application
and release.
BRAKE PEDAL STOP ADJUSTMENT
(Refer to Figure 5)
A pedal "stop" is provided on all school bus
models with air brakes to prevent driver from
bending or breaking push rod as the result of
exerting more pressure than necessary on the
brake pedal. It is important that this "stop" be
properly adjusted whenever service procedures
have been performed which might change the pedal-
to-valve relation. Adjust as follows:
1. Set emergency brake or block wheels.
2. Exhaust air from brake system .
3. Loosen lock nut and turn adjusting bolt and
stop plate assembly down as far as possible away
from brake pedal.
Sec. 5B
Page 211
AIR BRAKES