After getting the suspension sorted with the new Borla exhaust system, I went on a quick drive and found the rear axle was noisy, like marbles rolling inside a tin and the rear axle was wining louder the faster I drove.
When I put the car back up on stands and started testing things, I noticed a lot of noise on the drivers rear side of the axle. It really sounded like bearing noise, so I decided to replace the axle shafts and bearings to be on the safe side. The previous owner replaced the pinion bearing about 3 years before I owned it and there were no leaks. I assumed there should not be any other issues with the diff. Once I had the cover off, the oil was pretty much trash, though I didn’t find any major chucks or anything just typical gear wear and the gears looked evenly worn. I went ahead and replaced the axle shafts and bearings and added new seals. In the process I found the drivers side parking brake shoe was loose, you could easily grab it and shake it around. The lightbulb went off at this point, that the issue may not have been with the diff but with the parking brake. I got new shoes and brackets to hold them in and this time the new shoes were snugly installed. I refilled the diff with heavier oil and also added GM posi additive, even though some folks say not to add it for this style of rear axle (Torsen), there was a service bulletin from GM in the 2000’s that recommended adding the posi fluid to fix noise issues, so I did it. I figure it cannot hurt.
Results
Driving the car with new diff fluid made a big improvement, the wine at higher speeds is gone completely. There is a new rattle like sound in the driveline that is near unnoticeable. Further research I found that the Torsen style diffs are notoriously noisy. On the 4th gen forums as well as ls1tech some users recommend replacing the rear axle with an aftermarket 9″ as the solution, though others say the diff is fine unless you are heavily modifying your drivetrain. Researching the Ford 9″, it is a rather intense to install and only folks who race would truly take advantage of such a swap. I have met a couple 4th gen Trans Am owners that have made the conversion, apparently it is easy to do with my car (a non traction control model), but Trans Am’s with traction control the swap is more complicated.
The only remaining issue I have – the car stance is slightly off, the rear looks and feels a bit too low. Some weekend I will jack of the car and add a 1/2″ spacer to the spring upper rubber pads to lift the back a touch. Update: I added 1/2″ spacers in the spring pockets and that did the trick, perfect ride height! That week I took the car in for an alignment, it feels extremely dialed-in now.
Next post will cover the Apple Carplay/Android Auto system with rear backup camera installed, as well as back to projects for the 1981 Trans Am which includes a RetroSound Daytona M2 radio and New Vintage USA gauges. Stay tuned!