I started with an open diff drum rear end on my 1987 Firebird Formula. After a 350 swap, I wanted posi, so bought a rear end off craigslist that came off of a 1989 Firebird Formula. Now I am not certain that it is the orginal rear end off of that craigslist car, but it looks identical to mine except they put a strengthening diff cover on it and it has disc brakes.

I installed the rear end this weekend only to find out after mounting the tires that the tires now stick out past the rear fenders! The rims are the original for the 1987 car (non-concave 16" offset rims).

Are the rims the issue? Any remedies? Perhaps shorter axles? Thanks for any input!

 

93 and up should be 2-4" longer.

 

Those rims are for the drum setup. Did you actually measure the width of the rear?

See this thread, might help you.

https://www.thirdgen.org/forums/susp...ght=WIDE+TIRES

 

Sounds like you have a 93-7 or 98-02 rearend.

Rims are the same for disc and drum. However, there are front and rear wheels. Make sure you have them on correctly.

 

They were all the same width from '82 to '92. Disc brakes add about 1/2 inch to the total width, but that wouldn't make your tires stick out that much. The '93 to '02 rear ends were about 4 inches wider. Someone probably sold you a '93 or later rear end.

 

Thank you for all the quick replies! Interesting read on the offset rims. Would the 93+ rear ends still have all the same support mounting spots? I will have to measure it now. I had them side by side and they looked identical except for the brakes, so I just bolt it up. Though, I guess the handbrake cables were different.

The driver side tire sticks out about 1/2" outside the fender while the passenger side is more even with the fender. I kinda like the look, but I like my fenders as well!

I was thinking about swapping internals from the posi rear to the open diff. I don't care about the disc brakes. Is this a possibility? Guessing there are going to be issues with spline counts...

 

I learned there were front and rear designated wheels a couple years ago after the first tire rotation...but not until I drove it!

 

Your '89 should have 26 spline axles. This later rear end will have 28 spline axles. You can swap the internal parts, but you would have to get a set of 28 spline axles that are the correct length for your rear end.


Swapping internal parts is not as simple as taking them out and sticking them in. You must set the pinion depth, bearing preload and backlash any time you swap parts around in a rear end.