I have an 89 Camaro. It has had work done prior to me getting it. Many parts are out of many things. My latest problem is Rear Diff. I can not find any casting numbers. Tag is rusted. I did find these numbers on the diff. cover. P/N 10040660 I hope this means Part Number. 2.77 I believe this means 2.77 to 1 Gear Ratio. The last numbers are sn 12697 I believe this is Serial Number. It is a 10 bolt rear end. It has Disc brakes and is limited slip I think that is why it was put in. Any ideas what this may be out of or any other details please help. I'm becoming confused and at this point may have looked right at the answer and not realized it. Can anyone get me back on the right track?

There should be some numbers stamped on the front of the passenger side axle tube close to the center section. They're usually very hard to read. Those can tell you want year the diff is and what was originally inside it.

The only way to know for sure what's inside the diff is to pull the cover and have a look.

Welcome to TGO. Stephen 87 is right: The only certain way is to look. The following link may provide some info that will help ID what you have:

http://www.thirdgen.org/techboard/tr...-10-bolts.html (FAQ About 10-Bolts)

JamesC

Are you sure that it's a 10 bolt and not a 9 bolt? Look for Borg Warner cast into the center of the housing somewhere. Does it have a rubber plug in the cover? The 2.77 was a 9 bolt Borg Warner ratio. The 10 bolt was a 2.73. I don't remember the 10 bolt having any tags on them except for the "use limited slip differential fluid only" tag.

Thank you I was wrong I just went out and put my fingers on each bolt it is a 9 bolt not a 10. So first problem I can't count. Next yes it does have the rub check/fill plug. Third as soon is read your reply I remembered seeing may limited slips with the tag reminding you to use special fluid. There are 2 tags on this diff. both are on the cover. One is in the 1 or 2 O'clock position this one is rusted and unreadable but I think it is the limited slip tag. The second one with all the info is on the drives side of the diff cover and is at the 9 O'clock. It is held in place by 2 of the diff cover bolts. Does this make more since?

Since the 89 RS didn't come with a 9 bolt, you must assume the diff is not original. Unless you can read the data on the tag, it's probably better to just pull the cover and have a look. It would be a good chance to also change the diff oil since you have no idea how long it's been in there.

Factory production gear ratios that were available for the 9 bolt were 2.77, 3.27 and 3.45. A 3.70 ratio was available over the counter but never offered in a production vehicle. The 2.77 ratio was the only one in the 2 series. All the other ratios are in the 3 series.

Diff cover leaks and so does a wheel seal cover is coming off I’ll check gear ratio then. Bigger problem is the rear brakes. The passenger side caliper is mounted in front of the rear axle while the drivers’ side is to the rear. Passenger side all line up and look good and the E brake works. Drivers’ side does look right. I have a brake line going though the coil spring and I mean inter twined. That will have to be undone. It is not secured to anything between where it splits off and were it connects to the rubber brake line. The rubber brake line runs down and makes a true 180 upward and that has it kinked don’t think it is working real well. With the caliper the way it faces the drivers’ side parking brake faces the rear so the cable can not connect. I will most likely pull the 4 bolts out and flip it so things line up but when I go for parts I don’t know what to ask for. “I have an 89 camaro I need rear brakes and seals but I don’t know what axle I have” Thank you all for all the help. Any more Ideas I’m all ears. Again thank you all.

That's the OE configuration for all 82-88 rear disc cars. IIRC, there should be a hardline running directly to the driver's side caliper. Not so on the pass side, where the hardline is connected to a rubber line. BTW, an 89, if it was originally equipped with rear discs, would have had PBR's.

JamesC