GMC 4000 Series Service Manual page 224

which lifts plunger, moving inlet valve off seat.
This perm its flow of air from wet tank into column
section of valve. When brakes are released, air
pressure snaps actuator back in place, allowing
air and moisture in column to escape past plunger
seat through exhaust port of lower body to atmos­
phere. Spring then returns inlet seat and plunger
seat to "OFF" position. This action takes place
each time brakes are applied and released, there­
by operating a continuous process of moisture
ejection from brake air system .
The moisture ejector valve is NOT standard
equipment. It is offered as optional equipment only
on all 5500 and 6500 Series.
GENERAL
The brake application valves used on models
covered by this manual all operate on the same
basic principle. The physical shape of the valves
and the methods of mounting differ according to
model. There are three mounting types; tilt cab
models, conventional cab models,
models.
TILT CAB MODELS
The application valve is mounted on a support
bracket in an inverted position inside the cab. The
actuating push rod from the brake pedal extends
up through the bracket into the valve piston cup
as shown in figure 3. A breather tube is installed
in the exhaust opening in place of filter screens
and a hose connected to the tube carries the ex­
haust air down below the cab floor.
CONVENTIONAL CAB MODELS
The application valve on these models is fas­
tened to the cowl (fig. 4). The valve has two studs
as part of the assembly and one threaded bolt hole.
The valve is mounted inside the cab and studs ex­
tend through holes in cowl. Nuts and lock washers
are installed on studs on engine compartment side
along with one bolt to fasten valve securely to
cowl. A pedal bracket and pedal assembly is fa s­
tened to the bottom of the application valve by
three bolts. Pedal assembly contacts valve piston
with an upward movement. The exhaust port is on
the back side of the valve and exhaust air escapes
into engine compartment.
"COWL" MODELS
On these models, brake application valve is
mounted in a horizontal position on engine side of
dash. Valve assembly is attached to a mounting
bracket which is bolted to the dash panel. Brake
G M C S E R V I C E M A N U A L
REPLACEMENT (Refer to Fig. 13)
Removal
on cab step support and remove valve.
Installation
port and secure with attaching bolts.
operation of valve while applying and releasing
brakes. Check for leaks.
BRAKE APPLICATION VALVES
pedal is mounted inside the cab, with the actuating
push rod extending through the dash panel into the
valve piston cup as shown in figure 2.
APPLICATION VALVE REPLACEMENT
Ross and Bendix-Westinghouse application valves
and "cowl"
are interchangeable as complete assem blies (in­
cluding pedal). The component parts are not inter­
changeable. All valve ports, mounting holes and
brackets are located in the same relative places
to permit replacement of assem blies regardless of
manufacturer. The following procedures covering
removal and installation, apply to both Bendix-
Westinghouse and Midland-Ross valves.
TILT CAB MODELS
Removal
and drive out pedal to bracket pin.
assembly or valve only, block vehicle wheels or
hold by some means other than air brakes.
port.
to cab and remove complete assembly or:
which attach valve to support bracket and remove
valve.
Installation
tion on support bracket and attach with bolts or:
1. Exhaust air from system.
2. Disconnect air lines at valve.
3. Remove bolts which fasten valve to bracket
1. Position valve on bracket on cab step sup­
2. Connect air lines at valve.
3. Build up air pressure in system . Check
On all conventional cab models both Midland-
1. To remove pedal only, remove cotter pin
2. To remove pedal, valve and bracket as an
3. Drain air pressure from brake system .
4. Disconnect air lines from valve.
5. Disconnect exhaust hose from valve exhaust
6. Remove bolts which attach support bracket
7. If valve only is to be removed, remove bolts
1. To install valve only, place valve in posi­
Sec. 5B
Page 217
AIR BRAKES