IMPROVED BRAKE PEDAL FEEL (NEW VACUUM BOOSTER P/N). GMC Truck GMC C Pickup

MODEL: 1988 C/K 10 MODEL TRUCKS

THIS BULLETIN IS DIVIDED INTO 2 DISTINCT SECTIONS IN ORDER TO ADDRESS SEPARATE CONDITIONS WHICH OCCUR ON DIFFERENT BRAKING SYSTEMS. BOTH CONDITIONS MAY BE DESCRIBED BY THE CUSTOMER AS BRAKE PEDAL FEEL.

SECTION 1

Improved Brake Pedal Feel - JN3 Brake System:

Some customers may comment of hard brake pedal or lack of assist on some 1988 C/K trucks equipped with JN3 brakes (fourth digit of VIN is "D").BeginningwiththefollowingVlNbreakpoints, a new larger displacement brake vacuum booster will be installed on 1988 C/K 10 pickups with JN3 brake system. The new booster is being installed to improve power assist during braking and improve the"feel"ofthebrakes,especiallyforcustomerswho operate their vehicle heavily loaded most of the time.

Ft. Wayne - C1 GMC JZ 543800 K1 GMC JZ 544157

Oshawa - C1 GMC J1 564368 K1 GMC J1 564371

Pontiac - C1 GMC JE 528414 K1 GMC JE 528759

Customers with vehicles built before the VIN breakpoints who operate vehicles heavily loaded may prefer the improved brake pedal feel of the new booster If so, the brake booster which is currently being used in production can be installed on vehicles with this condition. When installing the new booster, follow the procedure in Light Duty C/K Service Manual X-8731, Section 5A.

Option New Booster Year Code Year Part Number ---- ---- ---- ----------- C/K 1 Under JN3 1988 18012114 6000 GVWR (Built before with power the above listed brakes VIN's)

For vehicles under warranty use: Labor Operation: H1220 Labor Time: 1.0 hr.

SECTION 2

Improved Brake Pedal Feel - JN5 Brake System.

Some customers may comment of a "spongy" or soft brake pedal feel, or longer brake pedal travel on some 1988 C/K trucks equipped with JN5 brakes (fourth digit of VIN is "E") tbat were built in the Oshawa Assembly Plant between the VIN break- points stated below. GMC vehicles build between J1545174 and J1552172

In order to improve the brake pedal feel, the master cylinder and brake vacuum booster combination listed below may be installed.

Master Cylinder New Brake Vacuum Booste P/N 18013977 P/N 18012114

Labor OP: T7660 Labor Time: 1.0 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.