SERVICE GUILD: 1989 ANTI-LOCK BRAKE CHANGE INFORMATION

SUBJECT: 1989 ANTI-LOCK BRAKE CHANGES

VEHICLES AFFECTED: 1989 C AND H CARLINES

THE FOLLOWING INFORMATION IS BEING PROVIDED TO POINT OUT SOME OF THE CHANGES THAT HAVE OCCURRED ON THE ANTI-LOCK BRAKE SYSTEM FOR THE 1989 C AND H CARLINES.

- THE 1989 ANTI-LOCK BRAKE SYSTEM HAS INCORPORATED SELF- DIAGNOSTIC CAPABILITIES WHICH CAN BE ACCESSED THROUGH THE ALDL CONNECTOR PIN H AND DISPLAYED THROUGH A FLASHING ANTI-LOCK LAMP.

- THE HIGH PRESSURE HOSE FROM THE PUMP TO THE BOOSTER IN THE HYDRAULIC UNIT HAS BEEN CHANGED TO A PIPE.

- THE MASTER CYLINDER BORE SIZE HAS BEEN INCREASED FROM 23.8 TO 25.4 MM AND THE BOOSTER ASSIST RATIO WAS CHANGED. IN ADDITION, THE FRONT CALIPERS HAVE CHANGED AND ARE NOW THE SAME AS THE CALIPERS USED ON NON-ABS EQUIPPED C AND H CARLINES.

- THE FRONT WHEEL SPEED SENSOR AIR GAP IS NO LONGER ADJUSTABLE. THE SENSORS MOUNT DIRECTLY TO THE KNUCKLE AND THE AIR GAP IS NOW SET CORRECTLY WHEN THEY ARE INSTALLED. IT IS IMPORTANT THAT THE ANTI-CORROSION COMPOUND (P/N 993037) BE APPLIED BETWEEN THE SENSOR BODY AND KNUCKLE DURING A SERVICE OPERATION.

- THE USE OF AN ANTI-CORROSION COMPOUND ON THE WHEEL SPEED SENSORS IS REQUIRED TO PREVENT THE SENSORS FROM CORRODING IN THE KNUCKLE.

- THE SENSOR WIRING IN THE VEHICLE HARNESS IS OF A TWISTED PAIR CONFIGURATION (PREVIOUS MODELS WERE OF A COAXIAL CABLE STYLE). THESE WIRES ARE SERVICED USING APPROVED GM WIRE REPAIR TECHNIQUES THE PIGTAIL ON THE SENSORS REMAINS COAXIAL CABLE AS BEFORE AND CANNOT BE SERVICED. PIGTAIL DAMAGE REQUIRES A SENSOR REPLACEMENT.

- THE MAIN RELAY AND PUMP MOTOR 30 AMP FUSES WERE REMOVED FROM THE SYSTEM. THESE CIRCUITS ARE PROTECTED BY FUSIBLE LINKS AT THE J- BLOCK

- A NEW TOOL J35604-88 IS AN ADAPTER WHICH IS TO BE USED WITH THE PRESSURE GAUGE ASSEMBLY TO CHECK ACCUMULATOR PRESSURE ON ALL 1989 TEVES ANTI-LOCK BRAKE SYSTEMS. ACCUMULATOR PRESSURE IS NOW CHECKED AT THE ACCUMULATOR PORT. FIGURE 5E1-2 ON PAGE 5El-4 OF THE 1989 C AND H NEW PRODUCT SERVICE MANUAL IS IN ERROR AND DOES NOT PROPERLY ILLUSTRATE THE USE OF THE PRESSURE GAUGE J-35604-88 ON A 1989 (ABS) SYSTEM. SEE FIGURE FOR CORRECT INSTALLATION.

FOR FURTHER INFORMATION ON THE 1989 ANTI-LOCK BRAKE SYSTEM REFER TO SECTION 5E OF THE 1989 C AND H NEW PRODUCT SERVICE MANUAL.

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.