Hello firebird and Camaro fans.

About 7 weeks ago I bought a 1986 Firebird base model that had been sitting for a while, and the dude I bought it from had swapped the 327 that was in there for a carbureted 350, mild build, roller cam. It has some 3 speed auto transmission, was going to be a drag car before I bought it. No heat or A/C. Now my problem is that I bought a nice set of rims and some staggered tires for it which fit nicely onto the car, however they are the wrong bolt pattern. The rims are 5x4.75 and the car is 5x4.5. Everywhere I’ve looked I’ve seen that firebirds and Camaros all have the same small GM bolt pattern, 5x4.75. Am I wrong? Were the axles swapped? Idk. I can buy adapters with a 1 inch space, it’s not a problem, but are all firebirds and Camaros 5x4.5?

anyway here’s the main problem. My dumbass cousins drive the car when I’m not home, and while doing a burnout on the crappy tires that are on it for now, they noticed that the rear brakes just weren’t there (front brakes weak as well but don’t worry about that). Now the rear brakes are drums, and the rear axle is an open diff. And since I want to street race the car, I originally wanted to at some point swap a Posi rear end with better gearing. Can I kill both birds with one stone? I found a Posi rear end from a late 4th gen Trans Am (3.43 gears) with disc brakes. I understand I’d need some conversion kit to make those brakes work on this older car, but how hard is it to bolt that rear end in?

another Reason I want to swap the rear axle is because it leaks fluid constantly. Lol. I don’t want to spend some $3,000 on a Hawks rear end because I am broke and this isn’t my only car, but I would like to know if the rear axle swap is possible. Thank you all very much, have a blessed day.

 

From what I understand and I have read on other forums, it will bolt right in, but the 4th Gen rear end is about 2" wider overall, so your wheels and tires would stick out.

 

GM did not use the 5 on 4½ pattern (the Frod & Xler one) on any cars anywhere near approaching full-size, including these.

These cars, and most other GM s of the era, used the GM 5 on 4.76" pattern. A few larger cars (I have a 74 Caprice convertible w 454, for example) used the 5 on 5 GM truck pattern.

If you were to have 5 on 4½" wheels on hand, they're not for that car. They're for a Frod or Xler. OTOH If you bought 5 on 4.76" ones and they fit, then that would be completely normal and expected. It would be astounding if they didn't.

The 4th gen rear also uses the 5 on 4.76" pattern. However the axles are about 1¾" longer on each side, as said. Their wheels are identical to ours except for the offset / backspacing, whatever you want to call that attribute. 3rd gen wheels on a 3rd gen car w 4th gen axle stick out that far on each side, and often will rub the fenders. They look stuuupid regardless. However, 4th gen wheels on a 4th gen rear in a 3rd gen car, is a total match for our cars' stock setup.

I'll note also, it is said that some BMW wheels, with 5 on 120mm pattern, will fit these cars acceptably, since 120mm = 4.724". Not quite "perfect", but in some circumstances, acceptable. Can't tell you which ones or whether the offset is right as I've never done it or seen it, only heard "roomers".

 

I wouldn't say 3rd gen wheels on a 4th gen rear look stupid or that they will rub.