3. Check the service brake chambers for leakage.
3.1 Apply the service brakes and hold them
on full line pressure of at least 80 psi
(550 kPa).
CAUTION
Do not overtighten the clamp ring. This can distort
the flange sealing surface, or the clamp ring itself.
3.2 Using soapy water, coat the service
chamber clamp ring. Leakage is exces-
sive if it produces a 1-inch (25-mm)
bubble within 5 seconds. See Fig. 1.On
Bendix service chambers, tighten the
clamp ring enough to stop the leakage,
but do not exceed the maximum torque
limits in Table 2.
Do not overtighten.
On other service chamber makes, if leak-
age is detected, tighten the clamp ring;
but do not exceed the maximum torque
limits in Group 42 of the
Business Class
®
Trucks Service Manual
.
Clamp Ring Torque Values (Bendix Chambers)
Description Torque: lbf·in (N·cm)
5/16–24 Nut 130–150 (1460–1700)
3/8–16 Nut 140–180 (1580–2040)
Table 2, Clamp Ring Torque Values (Bendix
Chambers)
3.3 If leakage persists, use the instructions in
Group 42 of the
Business Class
®
Trucks
Service Manual
to replace the service
brake diaphragm.
3.4 Using soapy water, coat the area around
the piston-rod bore. On some Bendix ser-
vice chambers loosen the boot, if neces-
sary. No leakage is permitted. If there is
leakage, use the instructions in the appli-
cable brake chamber section in Group 42
of the
Business Class
®
Trucks Service
Manual
and replace the service brake
diaphragm.
NOTE: On weatherproof Bendix chambers, the
leakage check can be performed at the cross-
drilled mounting stud.
Parking Brake Operation and
Leakage Checking
DANGER
Do not loosen or remove the parking brake clamp
ring (see Fig. 1) for any purpose at any time. The
parking/emergency brake section is not intended
to be serviced. Serious injury or death may result
from sudden release of the power spring.
Before doing any repairs or adjustments on a
service/parking brake chamber, read the appli-
cable warnings and instructions in the applicable
brake chamber section in Group 42 of the
Busi-
ness Class
®
Trucks Service Manual
.
1. Chock the tires.
2. Build the air pressure in the system to at least
100 psi (690 kPa), and shut off the engine.
3. Place the park control valve in the park position.
The brake should apply immediately. Then, place
the park control valve in the released position.
The brake should release immediately.
If the brakes do not apply or release as required,
see the air brake system troubleshooting guide in
the applicable brake chamber section in Group
42 of the
Business Class
®
Trucks Service
Manual
for possible causes and corrections.
WARNING
Do not disconnect the pressurized parking brake
hose. If disconnected under pressure, the parking
brake hose will whip as air escapes from the line,
and the air stream can direct dirt or sludge toward
persons in the area, which could result in injury.
4. Check the parking brake chambers for leakage.
4.1 With the park control valve released, ap-
ply soapy water around the parking brake
diaphragm clamp ring and at the drain
slots and exhaust breather on the body.
Disconnect the service brake hose at the
service port, and apply soapy water to
check for piston O-ring leakage.
Brakes 42
Business Class Trucks Maintenance Manual, October 1998 42/5
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