Whats that clunking noise from the rear when decelerating?
This noise is most common on cars with an automatic transmission. It usually occurs at downshift points where the rear gears disengage. Some people claim that changing the rear differential fluid and adding the rear diff additive (aka “limited slip oil”) fixes this. But in most cases it’s a problem with the PCM downshift program. A Technical Service Bulletin (#477124) addresses this in the 1993 – 1994 LT1 powered cars. The TSB describes a “3rd to 2nd downshift clunk” and calls for the computer program to be updated on all 1993 cars and all 1994 Pontiacs with a VIN sequence lower than 239227 and Chevy’s lower than 194422. All later cars should have the updated program.
