GMC 4000 Series Service Manual page 188

Conventional - behind cab step, immediately
below left-hand door. Vacuum reserve tank is lo­
cated in this same area, when used. See figure 19.
Tilt Cab - between frame side rails in front
of the radiator and behind the front bumper. See
figure 19.
P4500 - on the outside of the left-hand frame
side rail just ahead of the second frame cro ss­
member.
"S" Models - on the outside of the left-hand
frame side rail.
Some Models (both standard and optional) -
use the combined m aster-booster cylinder type
which is mounted on the dash panel in the engine
compartment. See figure 20.
REMOVAL (REMOTE MOUNTED)
1. For easier accessibility, it is recommended
that cab step be removed on conventional models
and that cab be tilted forward on tilt cab models.
2. Clean away as much road dirt and grease
as possible to prevent contamination of vacuum or
hydraulic system s.
3. Have suitable container available to catch
hydraulic brake fluid which will flow from system .
DO NOT RE-USE THIS FLUID.
4. Disconnect all hydraulic, vacuum, and at­
mospheric lines and hoses from power cylinder.
5. Remove bolts and nuts which fasten cylin­
der to vehicle frame and support brackets. Remove
power cylinder.
INSTALLATION (REMOTE MOUNTED)
1. Place power cylinder in position and fasten
with nuts and bolts to vehicle frame and support
brackets.
2. Connect all hydraulic, vacuum, and atmos­
pheric lines and hoses to power cylinder.
3. Bleed master cylinder and vacuum power
cylinder as directed under "Bleeding Brakes" in
this manual. If ONLY the power cylinder has been
removed, it should not be necessary to bleed the
wheel cylinders IF the master cylinder and power
cylinders are bled first AND lines to wheel cylin­
der have not been disturbed.
4. Start engine and test operation of brake sy s­
tem as directed. Refer to "Trouble-Shooting" chart
in this manual if operation is not satisfactory.
There are three different types of air cleaners
used on vehicles with vacuum assisted hydraulic
brakes.
SERVICING AIR CLEANERS
The air cleaner used on P4500, S5500, and
G M C S E R V I C E M A N U A L
V A C U U M POWER (
HYDRAULIC BRAKES
REMOVAL (DASH MOUNTED)
. 1. Clean away as much road dirt and grease
as possible to prevent contamination of vacuum or
hydraulic system s.
2. Have suitable container available to catch
hydraulic brake fluid which will flow from system .
DO NOT RE-USE THIS FLUID.
3. Disconnect hydraulic line from master cyl­
inder outlet.
4. Disconnect vacuum hose from vacuum check
valve in booster chamber.
5. Inside cab, disconnect push rod from brake
pedal.
6. Remove four bolts which fasten booster
and support bracket to fire wall and remove boos­
ter and master cylinder assembly with support
bracket from engine compartment.
INSTALLATION (DASH-MOUNTED)
1. Place power cylinder booster (with master
cylinder and support bracket attached) in position
on fire wall in engine compartment.
2. Install four bolts which fasten support
bracket to fire wall in engine compartment.
3. Connect vacuum line to check valve in
booster chamber.
4. Connect hydraulic line to master cylinder.
5. Inside cab, connect push rod to brake pedal.
6. Fill master cylinder with proper fluid. If
ONLY power cylinder has been removed it should
not be necessary to bleed wheel cylinders. Bleed
master cylinder as directed under "Bleeding Brakes."
7. Adjust brake pedal as directed.
8. Start engine and check operation of brake
system as directed. Refer to "Troubleshooting"
chart in this manual if operation is not satisfactory.
NDER AIR CLEANER
S6500 Models is the metal cup type which uses a
hog's hair type element. This cup is a friction fit
on the air intake pipe and can be removed by pull­
ing straight off. It can be cleaned and reused. Re­
fer to LUBRICATION (SEC. 0) in this manual for
service intervals and cleaning instructions. If
Sec. 5A
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