Brakes - Height Sensing Proportioning Valve Adjustment
Number: 85-210Section: 5
Date: JULY, 1986
Subject: HEIGHT SENSING BRAKE PROPORTIONING VALVE ADJUSTMENT PROCEDURE
Model and Year: 1984-1985 C/K 20 SUBURBANS
TO: ALL CHEVROLET DEALERS
This bulletin details a revision to the brake burnishing procedure, cancelling and superseding Chevrolet Dealer Service Bulletin 85-173 (Section 5) issued January, 1986. All copies of bulletin 85-173 should be destroyed.
The brake balance on 1984-1985 C/K 20 Suburbans can be adjusted in order to enhance rear braking performance under lightly loaded vehicle conditions.
In order to change brake balance, it will be necessary to adjust the height sensing brake proportioning valve. In addition, burnishing the brakes following the procedure below may be beneficial on some vehicles.
SERVICE PROCEDURE
Note: Always make sure that the brakes are operational after performing brake work and before returning the vehicle to service.
^ Raise vehicle, axle must be allowed to hang free (no load condition).
Valve Shaft:
^ Remove nut and disengage lever assembly from valve shaft (Figure No. 1).
Installation of plastic adjustment gauge:
^ Rotate valve shaft to permit installation of plastic adjustment gauge. Center "D" shaped hole of gauge must seat over "D" shape of the valve shaft and gauge tang must be positioned in valve mounting hole (Figure No. 2).
^ 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.
Note: DO NOT DRIVE THE LEVER ONTO THE SHAFT USING THE ATTACHING NUT. DOING SO MAY RESULT IN IMPROPER VALVE SETTING.
^ Reinstall valve shaft nut and torque to 8 - 11 N-m. (70-98 in.lbs.)
Cut gauge tang from body:
^ Cut gauge tang from body of the adjustment gauge to allow the valve assembly to rotate freely (Figure No. 3).
^ Lower vehicle and test brakes.
PARTS INFORMATION
Model P/N Description Code
Color
C20906 14061394 Gauge A
Green
K20906 15548904 Gauge E
Yellow
BRAKE BURNISHING
^ On dry clean level roadway, accelerate to 55 mph., observe traffic following and when its clear
^ 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