Hello All,

I recently bought an 1985 Trans AM. I have searched and searched and can't get a reliable answer. How do I tell if the previous owner has swapped out the rear end. I can not get a hold of the them, as they will not respond. It is a 10 bolt and is disc brakes. I can't find any identifying numbers on the rearend either. Any help would be greatly appreciated.

These pics won't help because they don't even show what wheels are on the car . A different of set wheel will move the tire in or out in relation to the body. Third and fourth gen rear end will look very much alike but are different width and have different brakes. More info ,like measurements and better pics are needed to identify what you have.

Most likely the wheels are not original...

If it's a 3rdgen axle, then there's a possibility, even a probability, that a 1985 Trans Am with disc brakes would've received a 9-bolt. You said it's a 10-bolt, but have you physically accounted for a 10th bolt in the center of the top of the cover? It's easily assumed that there's a tenth bolt up there, but if you haven't physically confirmed that, then please do so.

Regardless, in 1985, both, a 9-bolt and a 10-bolt will have the driver's side caliper on the rear of the rotor, and the passenger's side caliper on the front of the rotor. If that's yours, then you're confirmed.

Without knowing what wheels are on the car it's hard to say.

Just looking at it, assuming factory wheels or similar specs, the car has a 4th gen rear.

As said, 85 T/A would most likely have come with a 9-bolt. If there's a 10-bolt there now, most likely there's been some swappage going on.

I agree also, if your wheels are the stock ones for your car, that's probably a 93-up (4th gen) rear end. They stick out way too far and look kinda funny.

The brakes that LA described are the cast-iron Delco-Moraine ones from 88 or earlier. If it's truly from 85 and has discs, it should be those. If the calipers are aluminum, the rear isn't original, since those would be 89-up. Also, most 4th gen rears came with antilock brakes; there's a sensor in the top of the pumpkin, that of course wouldn't have anything hooked up to it in your car; that would be a quick way to identify one of those.