Clean off road grime from the relay valve, and any
debris from the valve exhaust port. Listen for air
leakage around the fittings or exhaust port. Tighten
the fittings as necessary. Use two wrenches to avoid
twisting the tubing.
If the valve fails this check, or is damaged, repair or
replace it; see the Midland service manual for in-
structions. Remove the chocks from the tires.
42–06 Quick Release and
Flipper Valves Checking,
Midland
Chock the tires. Start the engine and run it long
enough to pressurize the air system to at least 80 psi
(550 kPa), then turn off the engine.
Repeat as necessary, to maintain 80 psi (550 kPa)
pressure during these checks.
Clean off road grime from the valves, and any mate-
rial from the valves’ exhaust ports. Listen for air leak-
age around the fittings and exhaust ports. Tighten
the fittings, as necessary. Use two wrenches to avoid
twisting the tubing.
If any valve fails this check, or is damaged, repair or
replace it; see the Midland service manual for in-
structions. Remove the chocks from the tires.
42–07 Brake Chamber
Inspecting (All Models)
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
.
WARNING
Do not operate the vehicle with the front brakes
backed off or disconnected. Backing off or discon-
necting the front brakes will not improve vehicle
handling and may lead to loss of vehicle control
resulting in property damage or personal injury.
NOTE: Vehicles operating under severe or ad-
verse conditions should be checked more fre-
quently. If the brake chamber requires disas-
sembly, see Group 42 of the
Business Class
®
Trucks Service Manual for instructions.
1.
With the slack adjuster properly adjusted, check
the angle formed by the centerline of the piston
rod and slack adjuster. This angle should be
greater than 90 degrees in the released position
and approach 90 degrees in the applied position.
See
Fig. 2
.
At angles less than 90 degrees, brake chamber
force is reduced, which reduces braking
efficiency.
2.
Check each brake chamber for correct installa-
tion.
2.1
Check each mounting stud for the pres-
ence of prevailing torque locknuts and
hardened flatwashers. Make sure that the
hardened flatwashers are installed be-
tween the mounting bracket and the lock-
nuts. Do not install flatwashers touching
the service (non-pressure) chamber.
2.2
If the locknuts are loose, tighten them.
For correct torque values, see the appli-
cable brake chamber section in Group 42
of the
Business Class
®
Trucks Service
Manual
.
3.
Observe the piston rod engagement with the cle-
vis. Engagement of at least 7 threads is required;
there should be 1-inch (25-mm) clearance from
the centerline of the clevis pin hole to the end of
the piston rod. See
Fig. 3
. Adjust if needed.
4.
Brakes
42
Business Class Trucks Maintenance Manual, October 1998
42/2