AIR SYSTEM COMPONENTS
5. Make a series of brake applications and observe the
3. Test the operation of the valve by performing the
Maxibrake control knob. The knob should automatically
Operating and Leakage Test.
move inward, toward the dash panel, when the service air
pressure drops to approximately 28 psi (1.93 BARS). This
MAXIBRAKE CONTROL VALVE (39Z222)
pressure can be checked with the air gauge on the dash
DESCRIPTION. The Maxibrake control valve provides man-
ual driver control as well as automatic application of the
6. If the valve does not function as described above, or
Maxibrake safety chambers.
excessive leakage is present, it is recommended that the
valve be replaced or overhauled.
The Maxibrakes are released when the sir system is fully
merged and the Maxibrake Control Knob is pulled out.
Under these conditions, air pressure enters the valve at the
REMOVAL. To remove the Maxibrake control valve, pro-
inlet, port and flows through the drilled passage in the
ceed as follows:
to the outlet also applies pressure to the bottom of the
1. Open the drain cock on each reservoir to drain the air
shuttle, compressing the spring et the top of the shuttle.
pressure from the system. Check the Maxibrake control
This holds the valve in the open position as long aS the
knob to be sure that it is pushed in fully. This will vent any
service air pressure is sufficient to hold the spring in the
air pressure which may be in the Maxibrake safety cham-
If the service air pressure should drop to approximately 28
psi (1.93 BARS), the pressure at the bottom of the shuttle
2. Loosen the locknut and remove the knob. After the
would be insufficient to hold the valve in the open position.
knob has been removed, remove the locknut.
When this occurs, the spring at the top of the shuttle will
shift the shuttle to the closed position. This will block the
3. Disconnect the two air lines attached to the valve.
inlet port and connect the outlet port to the exhaust port,
allowing air pressure in the Maxibrake safety chambers to
4. Remove the mounting bolts and nameplate, and then
remove the valve.
The same sequence of events occurs when the shuttle
is shifted to the closed position manually by the
operator. This allows the operator to use the Maxi-
brakes as parking brakes.
OPERATING AND LEAKAGE TEST. To determine the
serviceability of the Maxibrake control valve, perform the
1. Block the wheels with wheel chocks to prevent move-
ment of the machine while performing this test,
2. Fully charge the air system.
3. Pull the Maxibrake control knob outward from the dash
panel, and check the rear wheel brakes. The brakes should
release when air is applied to the Maxibrake safety cham-
4. Coat the exhaust port of the Maxibrake control valve
Figure 9C-8. Maxibrake Control Valve (36Z222)
with soap suds to determine if leakage exists.