HEIGHT SENSING BRAKE VALVE ADJUSTMENT PROCEDURE & INFO
SUBJECT: HEIGHT SENSING BRAKE PROPORTIONING VALVE ADJUSTMENT PROCEDURE (SERV INFO) (Revised to change no.from 89-5-125 to 89-5-126)
VEHICLES AFFECTED: 1984-85 C2, K2 AND 86-89 R2, V2 SUBURBANS
THIS BULLETIN REVISED TO ADD 1986-89 R2 AND V2 SUBURBANS AND TO UPDATE THE PRODUCT SERVICE BULLETIN 85-5-113.
The brake balance on 1984-1985 C2 and K2 Suburbans can be adjusted in order to enhance rear braking performance under lightly loaded vehicle conditions. 1986-89 R2 and V2 Suburbans were built with this new brake adjustment.
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. The following service procedure should also be used on all 1984-89 suburbans if the height sensing linkage has been disconnected from the valve during routine service.
IMPORTANT: For vehicles exhibiting a hard brake pedal feel with a cold engine or upon quick brake reapply, reference Product Service Bulletin 88-5-127.
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 hand free (no load condition).
o Remove nut and disenge lever assembly from valve shaft, refer to Figure 1.
o Rotate valve shaft to permit installation of plastic adjustment gauge. Centre "D" shaped hole of gauge must seat over "D" shape if the valve shaft and gauge tang must be positioned in valve mounting hole, as shown in Figure 2.
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 in.lbs.).
o Cut gauge tang from body of the adjustment gauge to allow the valve assembly to rotate freely, refer to Figure 3.
o Lower vehicle and test brakes.
SERVICE PARTS INFORMATION
Model U-N Description Code Colour --------- -------- ----------- ---- ------- C2,R20906 14061394 Gauge A Green K2,V20906 15548904 Gauge E Yellow
BRAKE BURNISHING
o On dry clean level roadway, accelerate to 90 km/h (55 mph), observe traffic following and when its clear
o Apply brake at a deceleration rate of 2.5m (8 ft.)/sec/sec until vehicle speed is 40 km/h (25 mph). A decelerometer must be used to achieve the proper deceleration rate.
Repeat this procedure at 1.6 km (1 mile) intervals 15 times.
Decelerometers are available from various sources.
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.
