MCi Crusader II 1989 Maintenance Manual page 134

Date
2-1-89
Page ___
4 _- 4 _ _
MC-9 MAINTENANCE MANUAL
WARNING: Air pressure gauge on the dash
does not show parking brake reservoir
pressure; it shows dry tank pressure. If pres-
sure drops below 70-75 psi (483-517 kPa)
during operation, LOW AIR tell-tale will
flash and a warning buzzer will sound. The
coach should be stopped immediately and
the cause of the air loss corrected before
proceeding. A sudden automatic parking
brake application will result if
low
air pres-
sure warning signals are ignored during
operation.
RELEASE OF PARKING BRAKE
A. WHEN EMERGENCY PRESSURE HAS NOT DROPPED
MORE THAN 4 psi (27.6 kPa). After applying the parking brake,
push in handle of push-pul! valve. This applies reservoir pres-
sure to lock port of the actuator thereby releasing the locking
mechanism. At the same time, air pressure is also admitted to
the control port of the inversion valve which causes air to be
exhausted from the parking diaphragm thereby releasing the
brakes.
8.
WHEN EMERGENCY PRESSURE HAS DROPPED MORE
THAN 4 psi (27.6 kPa). After applying the parking brake, push in
handle of push-pull valve. Thjs applies reservoir pressure to the
'ocking port of the actuator which releases the locking mecha-
nism. Reservoir pressure is simultaneously applied to the con-
trol port of the inversion valve which in turn causes air to be
exhausted from the parking diaphragm. A heavy service brake
application will then produce sufficient forward motion of the
actuator piston rod to allow the locking mechanism to disen-
gage. Releasing the service brake application will restore the
system to normal running condition.
NOTE: If an Inadvertent senlce brake appli-
cation is made while the parking brakes are
applied,
the
parking brakes will
not
release
uni••• the handl• of the push-pull valve
I•
pushed In.
1. Button
2.
Spiral Pin
3. Nut
4. 0-Ring
5. Body
6. Inlet & Exhaust Valve
7.
Lockwasher
8. Machine Screw
9. O•Ring
10.
0-Rlng
11.
Elastic
Hex Nut
12. Bottom Cover
13. Piston
14. Sealing Ring
15. Spring
16. Plunger
PUSH-PULL CONTROL VALVE
The push~pull control valve is used to control the flow of air
to the parking ports of the rear brake chambers. It is mounted on
the driver's console to the right of the driver's position. See
figure 4-3.
Figure 4-3. Push-Pull Control Valve.
In normal operation. the push-pull control valve knob is
pushed down. To operate the parking and emergency brake.
the plunger is pulled upward to the top position. The system
then functions as outlined earlier in this section.
REMOVAL ANO INSTALLATION
1. Block or hold vehicle by some means other than air
brakes.
2. Vent air brake system. Disconnect the air lines from the
control valve. ·
3. Drive outthe spiral pin that holds the button on the control
valve plunger. Remove button. (See figure 4-4.)
4. Remove the control valve mounting nut. then the control
valve.
Before reinstalling, clean the air lines to the control valve and
brake actuators. Installation is the reverse of removal.
16
·14-0
~
6 ~
13-§
9 ~
1 0 ~
1 1 ~
i - - - - - -
' I
I I
I '
' , 2 ~
- ~
1-o
ei
- I
8 ~
Figure 4-4. Push-Pull Control Valve Parts Breakdown.