I want to swap in a new rear end into my 89 lo3. Just had a quick question: will any rear from a third gen fit? thanks

-chuck

 

any rear from any third or fourth gen f body will be a direct bolt in. there are a few other issues to consider but nothing that can't be over come.

 

The 4th gen rears will cause the tires to stick out past the wheel lips by about 1.5", unless you switch to different wheels. They aren't any stronger than the 3rd gen rears anyway.

Look for a later 3rd gen, particularly '89 and up. These use 28 spline axels instead of 26, and often have disc brakes (the aluminum PBR calipers are the ones to get if you can find them). If you can get a 9-bolt Borg/Warner they are a bit stronger than the 10-bolts. A Dana 44 was also offered in some special cars, and over the counter at GM, which is stronger still, though the odds of finding one are very slim. Definately snag a posi rear if you can, regardless of the model, but stay away from the Gov-Lock, because they aren't know for reliability.

If the rear you use has different gears than the one you have now you will need to swap the speedo gear to get the speedo to read right. Just something to think about.

 

so the forth gens bolt right in too? interesting, i never knew that. Can the speedo be fixed w/ a new computer chip or do you have to put the new gear in? where can i find this new speedo gear. The whole point of my swap is to get more gear than my open 2.73 gives me so i'll need to fix the speedo.
thanks
-chuck

 

Your car should have a mechanical speedometer, so you will need to switch the gear. GM sells them. There is a chart on this website that will tell you what one you need based on rear gear and tire size.

Yeah, the 4th gen rear bolts right in, but like I said the tires will stick out past your quarter panels. It looks pretty tacky, and most states won't allow you to pass inspection like that.