REDUCING DISC BRAKE COME BACKS (NEW TOOL KIT & POLICY CHANGE). Pontiac Sunbird 1994

REVISION 06/18/92

THIS BULLETIN IS BEING REVISED TO MODIFY THE POLICY STATEMENT AND REORGANIZE CONTENT. ______________________________________________________________________

REVISION 01/05/93

THIS BULLETIN IS BEING REVISED TO CLARIFY THE MANNER IN WHICH PARTS ARE TO BE RETURNED. THE REVISION IS THE LETTER AT THE END OF THE BULLETIN. ______________________________________________________________________

REVISION: 04/19/94

THIS BULLETIN IS BEING REVISED TO CANCEL THE RETURNING OF ROTORS FOR THE DEALERS. THE ATTACHED LETTER EXPLAINS THIS. PREVIOUS DIVISIONAL PUBLICATION NUMBER WAS: PONTIAC - 92-5-16. ______________________________________________________________________

REVISION: 06/10/94

THIS BULLETIN IS BEING REVISED TO INCLUDE ALL MODELS, ALL YEARS AND TO CHANGE THE LABOR OPERATION NUMBER. THIS BULLETIN REPLACES BULLETIN 235005 (GROUP REFERENCE 5 - BRAKES). ______________________________________________________________________

REVISION: 11/10/97

THIS BULLETIN OUTLINES GM'S PROCEDURES FOR BRAKE ROTOR SERVICE FOR ALL APPLICABLE GM PASSENGER CARS AND SUPERSEDES BULLETIN 235005A. ______________________________________________________________________

SUBJECT: INFORMATION ON BRAKE ROTOR WARRANTY SERVICE PROCEDURE

MODELS: 1994-98 GM PASSENGER CARS

IMPORTANT:

ROTORS SHOULD ONLY BE TURNED WHEN ONE OR MORE OF THE FOLLOWING ROTOR SURFACE CONDITIONS EXIST:

1. SEVERE SCORING - DEPTH IN EXCESS OF 1.5 MM (0.060 IN.).

2. PULSATION CONCERNS FROM:

A. THICKNESS VARIATION IN EXCESS OF 0.025 MM (0.001 IN.). B. CORROSION ON ROTOR BRAKING SURFACES.

ROTORS ARE NOT TO BE RESURFACED IN AN ATTEMPT TO CORRECT:

1. NOISE/SQUEAL.

2. COSMETIC CORROSION.

3. ROUTINE PAD REPLACEMENT.

4. DISCOLORATION AND/OR "HARD SPOTS".

EXPLANATION OF BRAKE ROTOR WARRANTY SERVICE PROCEDURE

RESEARCH AND TESTING HAS DETERMINED:

1. ROTOR REFACING DURING NORMAL PAD REPLACEMENT IS NOT NECESSARY.

2. ROTOR REFACING FOR COSMETIC CORROSION IS UNNECESSARY. CLEAN-UP OF BRAKING SURFACES CAN BE ACCOMPLISHED BY 10-15 MODERATE STOPS FROM 62-75 KM/H (35-40 MPH) WITH COOLING TIME BETWEEN STOPS.

3. ROTOR SERVICE IS INEFFECTIVE IN CORRECTING BRAKE SQUEAL, AND/OR PREMATURE LINING WEAR OUT, AND SHOULD NOT BE USED TO ADDRESS THESE CONDITIONS.

4. WHEN INSTALLING NEW ROTORS, DO NOT REFACE THEM.

5. ENSURE BEARING FLANGES ARE FREE OF CORROSION WHEN INSTALLING ROTORS TO PREVENT INDUCING LATERAL RUNOUT. USE KENT MOORE TOOL J 42450 TO CLEAN THE CORROSION AROUND THE WHEEL STUDS.

BRAKE SERVICE TECHNIQUES

EVERY BRAKE SERVICE SHOULD INCLUDE:

1. CLEAN AND LUBE ALL METAL-TO-METAL CONTACT POINTS (I.E.; CALIPER TO KNUCKLE, PAD TO KNUCKLE, ETC.).

2. CLEAN AND LUBE SLIDE PINS.

3. SET CORRECT CLEARANCES - CALIPER TO KNUCKLE, ETC.

4. CLEAN ROTOR AND HUB MOUNTING SURFACES. USE KENT MOORE TOOL J 42450 TO CLEAN AROUND WHEEL STUDS.

PULSATION:

BRAKE PULSATION CONCERNS MAY RESULT FROM TWO BASIC CONDITIONS:

1. THICKNESS VARIATION.

2. EXCESSIVE CORROSION.

ROTOR THICKNESS VARIATION IS THE RESULT OF UNEVEN ROTOR WEAR CAUSED BY EXCESSIVE LATERAL RUNOUT (>0.076 MM; >0.003 IN.). LATERAL RUNOUT CAN BE INDUCED BY:

1. DISTORTION OF THE BRAKING SURFACE BY APPLYING UNEVEN AND/OR EXCESSIVE WHEEL NUT TORQUE.

(THIS COULD BE THE RESULT OF A RECENT TIRE CHANGE, ROTATION, ETC.).

2. IMPROPERLY REFACING ROTORS.

BRAKE NOISE:

IMPORTANT - SOME BRAKE NOISE IS NORMAL.

BRAKE NOISE IS CAUSED BY A "SLIP STICK" TYPE VIBRATION OF BRAKE COMPONENTS. SOME INTERMITTENT BRAKE NOISE MAY BE NORMAL. PERFORMING 3-4 AGGRESSIVE STOPS MAY TEMPORARILY REDUCE OR ELIMINATE MOST BRAKE SQUEAL. IF THE NOISE PERSISTS, A BRAKE DAMPENING COMPOUND MAY BE APPLIED TO THE BACK OF EACH PAD. USE PERMATEX DISC BRAKE QUIET #126HB OR EQUIVALENT. ALSO, CLEAN AND LUBE ALL METAL-TO-METAL CONTACT AREAS BETWEEN PADS, PAD GUIDES, CALIPER AND KNUCKLES WITH A THIN LAYER OF HIGH TEMPERATURE SILICONE GREASE. THIS ALLOWS PARTS TO SLIDE FREELY AND NOT VIBRATE WHEN MOVING RELATIVE TO EACH OTHER.

ROTOR GROOVING

EXCESSIVE GROOVING CAN BE CAUSED BY FOREIGN MATERIAL IN CONTACT WITH THE ROTOR, BUT MOST OFTEN ROTOR GROOVING IS THE RESULT OF NORMAL BRAKE WEAR. DO NOT RESURFACE ROTORS FOR LIGHT GROOVING. RESURFACE ROTORS ONLY WHEN GROOVES OF 1.5 MM (0.060 IN.) OR DEEPER ARE PRESENT.

A DIME MAY BE USED TO DETERMINE DISC BRAKE GROOVE DEPTH. PLACE A DIME IN THE GROOVE, WITH ROOSEVELT'S HEAD TOWARD THE GROOVE. IF THE DIME GOES INTO THE GROOVE BEYOND THE TOP OF HIS HEAD, THE GROOVE EXCEEDS 1.5 MM (0.060 IN.) AND THE ROTOR SHOULD BE SERVICED. (IN CANADA, IF ANY PORTION OF THE LETTERS OF "IN CANADA" ARE COVERED, THE ROTOR SHOULD SERVICED.) IF THE GROOVE IS TOO NARROW FOR THE DIME TO BE INSERTED, IT IS NOT A CAUSE FOR CONCERN.

HIGH PEDAL EFFORT

FOLLOW SERVICE MANUAL DIAGNOSTIC PROCEDURES FOR THIS CONDITION. SERVICE ROTORS IF THEY HAVE BEEN RECENTLY RESURFACED. (THE SURFACE FINISH MAY BE OUT-OF-SPECIFICATION).

LIGHTLY RUSTED ROTORS

LIGHT SURFACE RUST ON ROTOR BRAKING SURFACES IS OFTEN COSMETIC AND CAN BE ELIMINATED DURING A FEW NORMAL DRIVING STOPS. RUSTING MAY OCCUR WHEN A VEHICLE IS NOT DRIVEN FOR EXTENDED PERIODS. ROTORS WITH SURFACE RUST ON UNSOLD NEW CARS CAN USUALLY BE BURNISHED CLEAN BY PERFORMING 15 MODERATE STOPS FROM 62-75 KM/H (35-40 MPH) WITH COOLING TIME BETWEEN STOPS.

FACTS ABOUT BRAKE SERVICE

O ORIGINAL EQUIPMENT ROTOR SURFACES ARE GROUND TO ENSURE SMOOTH FINISH AND PARALLELISM BETWEEN MOUNTING AND FRICTION SURFACES. NEW ROTORS SHOULD NOT BE RESURFACED BEFORE INSTALLATION.

O IMPROPER TIGHTENING OF WHEEL NUTS CAN INDUCE LATERAL RUNOUT (DISTORTION OF BRAKING SURFACES) WHICH WILL LEAD TO UNEVEN WEAR. AS HIGH SPOTS ARE WORN DOWN, RESULTING THICKNESS VARIATION WILL CAUSE BRAKE PULSATION.

O ENSURE WHEEL BEARING FLANGE IS CLEAN AND FREE OF CORROSION BEFORE INSTALLING NEW ROTORS. A NEW ESSENTIAL TOOL (KENT MOORE TOOL J 42450) WILL SOON BE SENT TO ALL DEALERS. THIS TOOL MAKES IT EASIER TO CLEAN CORROSION AROUND THE WHEEL STUDS.

O ALWAYS MARK THE POSITION OF ROTOR ON THE HUB BEFORE REMOVAL, AND REINSTALL THE ROTOR IN THE SAME POSITION.

O ROTORS WITH PERCEIVED HARD SPOTS OR DISCOLORATION SHOULD NOT BE SERVICED. THESE CONDITIONS ARE NORMAL.

O INSTALLATION OF NEW ROTORS DOES NOT REQUIRE PAD REPLACEMENT. DO NOT REPLACE PADS UNLESS THEIR CONDITION REQUIRES IT.

O IT IS NOT NECESSARY TO REPLACE ROTORS IN PAIRS. ROTORS MAY BE SERVICED INDIVIDUALLY.

O A TORQUE LIMITING SOCKET OR TORQUE WRENCH MUST BE USED TO INSURE THAT THE WHEEL NUTS ARE TIGHTENED TO SPECIFICATION. THIS SHOULD BE DONE IN 3 STEPS USING THE STAR PATTERN.

1. SNUG THE NUTS DOWN BY HAND. 2. USING THE STAR PATTERN AND A TORQUE LIMITING SOCKET OR TORQUE WRENCH, TIGHTEN THE WHEEL NUTS TO ABOUT HALF THE FINAL TORQUE. 3. TIGHTEN THE WHEEL NUTS TO SPECIFICATION USING THE STAR PATTERN AND A TORQUE LIMITING SOCKET OR TORQUE WRENCH.

O NEVER USE LUBRICANTS OR PENETRATING FLUIDS ON WHEEL STUDS, NUTS, OR MOUNTING SURFACES. WHEEL NUTS, STUDS, AND MOUNTING SURFACES MUST BE CLEAN AND DRY.

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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 BULLET IN 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.