I have a 88 GTA with some rear end issues. The car originally came with a 9 bolt rear end with 3.27 gears in it. Unfortunately the original gears were trashed the pinion gear had a giant crack in it and ring gear was toast so the car made a horrible whining/humming sound while driving. Went to a shop and they recommend putting a 3.70 gear ratio in since GM does not make the 3.27 gear ratio anymore. After spending over $1000 having them replace it i get the car back after two weeks of the car sitting outside through hellish weather only to discover the gear whine is still there but not as loud and upon decelerating the rear end will make a loud popping noise and the car will jerk violently before coming to a stop. The car went back to the shop 3 days later they told me nothing was wrong i haven't been back since and do not plan on returning anytime soon. I feel I should just find a nice used rear end with the original gear ratio instead of messing with this one. If anyone could give me any info as to what may be wrong id appreciate it thanks.

 

Every 3.70 gear that I have seen for the 9 bolt makes noise. It doesn't matter how well it is set up it will make noise.


The popping noise may be the cones in the differential breaking loose. Try adding a bottle of the GM limited slip oil additive and drive it for a few days and see if it gets better. This will not help with the whine but the pop may go away. Also be sure that the air pressure in the rear tires is equal and that the tire size and tread wear is equal.