HEIGHT SENSING BRAKE VALVE ADJ PROPORTIONING VALVE ADJUSTMENT
SUBJECT: HEIGHT SENSING BRAKE PROPORTIONING VALVE ADJUSTMENT PROCEDURE
MODELS: 1991 C3500 HD TRUCKS
The following service procedure describes how to adjust the height sensing brake proportioning valve on 1991 C3500 HD trucks.
This procedure should be used whenever the height sensing linkage has been disconnected from the height sensing brake proportioning valve during routine service. This adjustment is made during assembly on all 1991 C3500 HD trucks.
SERVICE PROCEDURE
Note: Always make sure that the brakes are operational after performing brake work and before returning the vehicle to service.
o Raise vehicle, axle must be allowed to hang free (no load condition).
o Remove nut and disengage lever assembly from valve shaft (Figure 1).
o Rotate valve shaft to permit installation of plastic adjustment gage. Center "D" shaped hole of gage must seat over "D" shape of the valve shaft and gage tang must be positioned in valve mounting hole (Figure 1).
o Reinstall lever assembly to the valve shaft utilizing a "C" clamp or channel lock pliers to seat lever nylon bushing to serration on the valve shaft.
[!] Important Do not drive the lever onto the shaft using the attaching nut. Doing so may result in improper valve setting.
o Reinstall valve shaft nut and torque to 8-11 N.m. (70-98 lbs. in.)
o Cut gage tang from body of the adjustment gage to allow the valve assembly to rotate freely. Lower vehicle and test brakes.
SERVICE PARTS INFORMATION
Part Number Description Quantity Required ---------- ----------- ----------------- 15592484 Gage 1
Parts are currently available from GMSPO.
BRAKE BURNISHING
o On dry clean level roadway, accelerate to 55 mph., observe traffic following and when its clear
o Apply brake at a deceleration rate of 8 ft/sec/sec until vehicle speed is 25 mph. A decelerometer must be used to achieve the proper deceleration rate.
Repeat this procedure at 1 mile intervals 15 times. Decelerometers are available from various sources, one of which is:
Ammco Tool Company 2100 Commonwealth Avenue N. Chicago, IL 60064
If a decelerometer is unavailable the braking should be of a constant application bringing the vehicle speed from 55 mph to 25 mph in approxi- mately 5-6 seconds.
WARRANTY INFORMATION
For vehicles repaired under warranty use: Labor Operation: H0777 Labor Time: 0.3 hr.
General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.
