MCi Crusader II 1989 Maintenance Manual page 145

Date
1-1-89.
4-15
Page· _ _ _ _
MC-9 MAINTENANCE MANUAL
or yearly, the inlet and· exhaust valves. exhaust diaphragm,
0-rings and rubber graduating spring should be replaced if
they show signs of wear or deterioration.
Every 7,200 operating hours or 200.000 miles (320,000 km)
or every two years. disassemble the brake valve. clean and
inspect all parts. Install new parts where they are found to be
worn or damaged.
SERVICE CHECK
Check the service and emergency circuits_ using test gauges
known to be accurate. Depress the pedal to several positions
between the fully released and fully applied positions and
check the delivered pressure on the test gauge to see that it
varies equally and proportionately with the movement of the
brake pedal.
After a full application is released. the reading on the test
gauge should promptly fall off to zero. Service brake delivery
pressure will be about 2 psi (13.8 kPa) greater than the emer•
gency brake delivery pressure with both supply reservoirs at
the same pressure. This is a normal condition.
WARNING: A change in vehicle braking
characteristics or a low pressure warning
may indicate a malfunction in one or the
other brake circuit. Although the vehicle air
system may continue to function, the vehi-
cle should not be operated until the neces-
sary r~pairs have been made. Always check
the vehicle brakes after performing brake
work and before returning the vehicle to
service.
LEAKAGE CHECK
1. Coat the exhaust port and body of the brake valve with a
soapy solution. See figure 4-15.
2. Make and hold a brake application to 80 psi (552 kPa).
3. Leakage permitted is a one inch (25.44 mm) bubble in
three seconds.
If the brake valve has excessive leakage. it can be repaired.
REMOVAL
1. Block the coach wheels and vent the air system reservoirs
by opening the drain cocks.
2. Disconnect atl supply and delivery structural lines at the
brake valve.
NOTE: Tag all air lines and their relation to
the brake valve for reconnection.
3. Remove the mounting bolts and the brake valve.
DISASSEMBLY
1 If the entire brake·valve and lever assembly was removed
from the vehicle. remove the stop light switch and remove the
-tnree capscrews securing the treadle assembly to the basic
brake valve.
2. Remove the screw securing the exhaust diaphragm and
washer to the exhaust cover.
3. Remove the four screws that secure the exhaust cover to
the lower body.
4. Remove the emergency inlet and exhaust valve assembly
from the lower body.
5. Disassemble the emergency inlet and exhaust valve
assembly by removing the retaining ring. Separate the washer.
0-ring retainer. both 0-rings. the spring and the valve retainer.
6. Remove the four hex head capscrews securing the lower
body to the upper body and separete the body halves.
7. Remove the rubber seat ring from the lower body.
8. While applying thumb pressure to the No. 1 piston. lift out
and up on the three lock tabs of the No. 1 piston retainer.
9. Using a ¾" wrench. hold the ESNA nut on the threaded
end of the stem on top of the No. 1 piston. Insert a screwdriver in
the exhaust passage through the center of the valve and
engage the slotted head of the stem.
WARNING: The combined force of the
intemal springs is approximately SO lbs.
(22.6 kg). Care must be taken when remov-
ing the ESNA nut as the spring forces will
be released. The No. 1 piston and relay
piston must be manually or mechanically
contained while the nut an~ stem are being
removed.
10. Rotate the screwdriver counterclockwise and remove
the stem. stem spring, spring guide, and ESNA nut
11. Remove the relay piston, relay piston spring from the
upper body.
12. Disassemble the No. 1 piston by rotating the spring seat
nut counterclockwise. Separate the spring seat nut. spring seat.
rubber spring and remove the piston 0-ring.
13. Remove the large and small 0-rings from the relay
piston.
14. Remove the retaining ring securing the service brake
inlet and exhaust valve assembly in the upper body and remove
the valve assembly.
15. Disassemble the service brake inlet and exhaust assem-
bly by removing the retaining ring and separating the washer,
0-ring retainer, both 0-rings. valve spring and valve retainer.
CLEANING ANO INSPECTION
Wash all metal parts in cleaning solvent and dry them.
Inspect all parts for excessive wear or deterioration. Check the
springs for cracks, corrosion, or a permanent "set" Replace all
rubber parts.
REASSEMBLY
Prior to assembling the brake valve. coat all 0-rings, 0-ring
grooves, piston bores and metal-to-metal surfaces with sili-
cone base lubricant.. TMC/ MCI Part No. 21-7512-11.
1. Reassemble the service brake inlet exhaust valve assem-
bly by first placing the valve retainer and the valve spring over
the inlet and exhaust valve.
2. Place the 0-ring retainer with _the 0-ring grooves away
from the spring, over the inlet and exhaust valve and install the