FINAL DRIVE NOISE CAUSE AND CORRECTION

SOME 1981 FINAL DRIVE UNITS WERE ASSEMBLED WITH INCORRECT PRELOAD (TOO LOW) ON THE PINION BEARINGS WHICH RESULTS IN A NOISE THAT CAN BE HEARD WHILE DRIVING THE VEHICLE. NORMAL DIAGNOSIS PERFORMED AT THE DEALERSHIP INCLUDES A STEP FOR CHECKING THE PRELOAD. HOWEVER, PRELOAD READINGS ON USED UNITS ARE NORMALLY NEGLIGIBLE 0.6 N.M (5 IN. LBS. OR LESS) AND MAY NOT QUICKLY LEAD TECHNICIANS TO THIS CAUSE OF THE NOISE CONDITION. FURTHER INSPECTION ON THESE NOISY UNITS ALSO REVEAL LITTLE OR NO RING AND PINION BACKLASH AND AN UNUSUAL TOOTH CONTACT PATTERN. THESE NOISY FINAL DRIVES SHOULD NOT REQUIRE GEARSET REPLACEMENT UNLESS THE GEARSET HAS BEEN SCORED. TO CORRECT UNITS THAT EXHIBIT THIS NOISE CONDITION, FOLLOW PROCEDURES IN THE APPROPRIATE SECTION OF THE 1980 SERVICE MANUAL. THE FOLLOWING ITEMS SHOULD BE CHECKED DURING THE PROCEDURE: - INSPECT GEARSET. REPLACE ONLY IF SCORED. - REPLACE PINION BEARINGS AND SPACER. - MEASURE CASE FOR PINION DEPTH WITH NEW BEARING. - REASSEMBLE TO SPECIFICATIONS AS NOTED IN THE 1980 SERVICE MANUAL INCLUDING PRELOAD, ETC. - FINAL DRIVE DATE CODED 320 (320TH DAY - NOVEMBER 15TH) OR LATER SHOULD NOT HAVE THIS CONDITION.

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.