MCi Crusader II 1989 Maintenance Manual page 146

Date
1-1-89
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MC-9 MAINTENANCE MANUAL
0-rings in their proper grooves.
3. Place the washer over the inlet and exhaust valve. against
the 0-ring retainer and 0-rings. and install the retaining ring.
4. Install the service brake inlet and exhaust assembly in the
upper body and replace the retaining ring to secure it. Be sure
the retaining ring is seated completely in its groove.
5. Install the large and small 0-rings on the No. 2 relay
piston.
6. Replace the No. 1 piston 0-ring in the piston 0-ring
groove.
7. Install the rubber spring, concave side down. in the No. 1
piston. Place the spring seat. flat side up, over the rubber spring.
8. Install the No. 1 piston spr.ing seat nut. with its hex closest
to the spring seat. and rotate clockwise until the top surface of
the spring seat is even with the top surface of the piston.
9. Place the No. 1 piston return spring in the upper body
piston bore.
10.
Install the No. 1 piston, spring seat out over the return
spring and press the piston into the body bore.
1 1. Place the No. 2 relay piston return spring in the upper
body and place the No. 2 relay piston over the spring, so that the
concave side of the piston ls against the spring.
12. Compress both the No. 1 piston and relay piston into the
upper body and hold them compressed, either manually or
mechanically.
13. Place the stem through the exhaust passage of the lower
body so that the threaded portion is visible at the No. 1 piston.
14. Using a screwdriver to engage and hold the slotted head
of the stem, install the stem spring and spring seat. Make certain
all three lock taps have engaged and outer lip of the body.
15. Reassemble the emergency brake inlet and exhaust
valve assembly as referenced in steps 1, 2 and 3 of this section.
16. Install the emergency brake inlet and exhaust valve
assembly in the lower body.
17. Place the exhaust cover on the lower body and install the
four machine screws with lockwashers. to secure itto the body.
18. Tighten the four machine screws to 20-30 inch pounds
(2.3-3.4 Nm) torque.
19. Install the exhaust diaphragm and diaphragm washer
to
the exhaust cover using the Phillips head screw and lock-
washer.
20. Install the seal ring in the lower body and secure the
lower body to the upper body using the four hex head cap-
screws and lockwashers.
21. Tighten the four capscrews to 70-100 inch pounds (7.9-
11 Nm) torque.
22. Install the lever assembly to the basic brake valve using
the three capscrews and lockwashers and tighten to 80-100
inch pounds (9-11 Nm) torque.
23. Install stop light switch.
SHUTTLE VALVE
The shuttle valve is located under the entrance floor in the
tire compartment (figure 4-16). Under normal conditions the
shuttle valve does not play an active role in the braking system.
When a loss of air is experienced in the service brake system
creating a pressure difference of 30 to 40 psi (207 kPa) between
the service and emergency brake systems. the shuttle valve
piston is moved upward. This allows air pressure from the
parking tank to be modulated by the brake valve to apply the
rear brakes.
Virtually no maintenance is required on the shuttle valve.
There is a breather hole on the body of the valve and some air
Figure 4-15. Brake Valve Installed.
Figure 4-16. Shuttle Valve Installed.
may exhaust from it (listen for hissing sound). If the leak con-
tinues while the brakes are fully applied. the valve should be
removed, disassembled. and the 0-rings replaced.
TESTING
The valve can be tested to see if the piston in the valve
shuttles (moves) to allow parking brake air pressure into the
brake lines, by simulating an emergency loss of air pressure
from the service tanks.
1. Place an air pressure gauge in the brake line between t.,e
shuttle valve and the check valve.
2. Build up air pressure until the governor cuts out
3. Turn off the engine and vent the dry and wet tanks by
opening the drain cocks.
4. Apply the brakes and check the air pressure gauge. Air
pressure from the parking brake tank will apply the rear brakes
as if braking in an emergency situation (loss of service brakes).
The brake valve has a modulating feature: as more pressure is
applied to the brake valve, there is an increase in brake line
pressure.
Once the drain cocks are closed and pressure built up to
normal in the service tanks, the piston in the shuttle valve will