FRONT BRAKE CALIPERS (NEW P/N)

VEHICLES AFFECTED: 1984-86 C, 1986-87 R, 1984-1988 G

New front brake calipers for the models listed above are now available from CANSPO. These new calipers have smoother bore finishes. If caliper replacement is being considered to correct a braking induced directional lead (either right or left) the following inspections and procedures should be performed. Evaluation of a vehicle's brake performance is not intended to be made with the vehicle operator's hands removed from the steering wheel. Vehicles that exhibit directional bias under these conditions are not considered to exhibit brake lead.

Before road testing the vehicle, perform the following services:

Preliminary Inspection

. Inspect tires for excessive, uneven wear - replace if necessary. . Equalize tire pressures. . Equalize parking brake adjustment. . Adjust rear service brakes to .030"running clearance. . Check and if necessary, adjust the front end alignment, including toe. . Inspect caliper brake line bolt (#34, page 5A8, Figure 4, 1988 R/V/G/P Service Manual ) for proper location of orifice. The orifice should be located in the unthreaded part of the bolt. If the orifice is located in the threaded portion of the bolt then the bolt must be replaced.

IMPORTANT: After the preceding inspections and/or adjustments have been made, the vehicle should be road tested to verify if a lead still exists. Vehicles that lead may lead either right or left when the brakes are applied.

Make all stops on a dry, level (no crown), clean roadway.

Important

Each applicable step must be thoroughly completed to effect a lasting repair. Failure to complete the procedure exactly as written may result in an unsatisfactory repair.

Safely conduct a series of 5 stops from 90 kph bringing vehicle to a stop in 5 seconds (16 FPS Sq.). Record amount and direction of lead. Do not slide or lock wheels.

* FPS Sq. or Ft/Sec2 is the measurement used for calculating the deceleration rate with a decelerometer. Use of decelerometer, when available, is the preferred method.

PROCEDURE A

Right or left lead

Remove and discard the brake calipers and pads

Refinish brake rotors per Chart 1 (or replace brake rotors if they cannot be brought into spec.)

Inspect and/or adjust front wheel bearing per the procedure in Service Manual Section 3C

Install new Delco Moraine brake calipers See Parts Information for parts numbers

Install new Delco Moraine brake pads

Bleed front brakes

Inspect caliper to knuckle clearance (.010 -.024 In. total). If necessary, file knuckle to obtain clearance. Equalize all upper and lower clearances. See Figure #1.

Perform 12 stop burnish procedure. Burnish procedure is mandatory.

12 Stop burnish procedure

lst Stop From 65 kph taking 6 seconds to stop (10 FPS Sq.)* 2nd Stop To llth Stop From 90 kph taking 5 seconds to stop (15 FPS Sq.)* 12th Stop From 65 kph taking 6 seconds to stop (10 FPS Sq.)*

Drive (0.8) km. between burnish stops. Drive 6.5 km. after 12th stop to cool system.

To confirm if vehicle is repaired, conduct series of 5 stops from 90 mph bringing ----- No Lead vehicle to stop in 5 seconds (15 FPS Sq.).

Record results and compare to initial stops

Parts are currently available from CANSPO.

New Parts Information:

Brake Old Caliper New Caliper System Part Number Part Number ------- ---- ------ -----------

JBl and 3 18012308 LH 18015427 LH 18012309 RH 18015428 RH

JB5 and 6 18007947 LH 18015383 LH 18007948 RH 18015384 RH

JB7 18009753 LH 18015385 LH 18009754 RH 18015386 RH

CHART 1

Good contact is important between the friction surfaces of the brake system. With semi-metallic linings, it is important to have good re-finished rotor surfaces. A poor finish on one rotor can result in reduced brake effectiveness. This may result in a brake lead condition if installed opposite a properly finished rotor.

The original equipment new disc brake rotors have an initial surface finish of 20 to 60 micro-inches and all have a non-directional swirl pattern.

SERVICE RECOMMENDATION

. Rotor refinish reqiures a micro-inch surface refinish equivalent to the new vehicle rotor specification.

. The recommended procedure for obtaining this finish is as follows:

Rough Cut Finish Cut --------- ---------- Spindle Speed 200 RPM 200 RPM Depth Of Cut Per Side .005" .002" Tool Cross Feed Per Rev. .006"-.010 " .002" Max. Vibration Dampener Yes Yes Swirl Pattern - 120 GRIT No Optional*

*Duplication of new rotor and smoother finish for best initial brake effectiveness.

When installing new rotor from service stock "do not" refinish the surface as these parts are to recommended finish.

When refinishing brake rotors the following is important:

. The brake lathe must be in good working order and have capability to produce the intended surface finish.

. Use correct tool feed and arbor speeds. Too fast a speed or too deep a cut cam result in a rough finish.

. Cutting tools must be sharp.

. Adapters must be clean and free of nicks.

. Lathe finish cuts should be further improved and made nondirectional by dressing rotor surface with a standing disc power tool (AMMCO Model 8350 Safe Swirl Disc Rotor Grinder or equivalent).

. Rotor surfaces are to be refinished to 20 to 60 micro-inch.

To become familiar with the required surface finish, drag a fingernail over the surface of a new rotor from parts stock or one on a new vehicle. If your brake equipment cannot produce this smooth a finish when correctly used, contact the equivalent manufacturer for corrective instructions.

The clearance between the the caliper and the steering knuckle upper and lower must be equal right and left. When right and left clearances have been equalized, add one upper and one lower and the total should be between 0.26 - 0.60 mm (0.010 - 0.024 inches). File knuckle to obtain the proper clearances.

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.