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

IMPROVED BRAKE PEDAL FEEL (NEW VACUUM BOOSTER P/11).

VEHICLES AFFECTED: 1988 C/K TRUCKS ----------------- THIS BULLETIN IS DIVIDED INTO 2 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" ). Beginning with the following VIN breakpoints, 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" of the brakes, especially for customers who operate their vehicle heavily loaded most of the time. C10 GMC JZ 543800 C15 CHEV JZ 256482 Ft. Wayne - K10 GMC JZ 544157 K15 CHEV JZ 257952

C10 GMC J1 564368 C15 CHEV J1 256582 Oshawa - K10 GMC J1 564371 K15 CHEV J1 256583

C10 GMC JE 528414 C15 CHEV JE 181848 Pontiac - K10 GMC JE 528759 K15 CHEV JE 182896

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 l Under JN3 1988 18012114 6000 GVWR (Built before with power the VIN's)

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") that were built in the Oshawa Assembly Plant between the VIN breakpoints stated below.

Chevrolet vehicles built between J12Q6556 and J1233550

GMC vehicles built 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 Booster --------------- ------------------------ P/N 18013977 P/N 18012114

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.