Can the rear out of a 4th gen be bolted right in a
3rd gen car? If not what mods are needed?

 

if you have a disc brake car, the rear should be a direct bolt in. Even drum brake rear end thirdgens should be a direct bolt in, but you'll have to check the rear brake line connection from the car's body to the rear end. i do believe its the same as the disc brake 3rd gens.

for drum cars, you'll need a disc brake proportioning valve. some ppl tho have used the drum one without problems...but i'd do the disc brake one anyway just to be safe

 

and 4th gen rears are wider

i was going to opt for a posi drum 4th gen rear for my 82 so i could dump the 2.73 open junk but too many things are different for my taste
so im going to stick with a 3.42 or 3.73 third gen rear

 

other than being wider, everything else will bolt up including torque arm, shocks and springs, and lower control arms. can reuse thirdgen sway bar.

 

How much wider? What gears come in them? Are all 4 gen Tran Am rears posi?

 

check this thread i made about my swap... pics inside.
https://www.thirdgen.org/forums/faq-...-gen-rear.html

basically they all should be posi if its a trans am. generally its 3.23's or 3.42's gears. some had a 2.73s but trans ams should have one of the higher gears

EDIT. forgot that E brake cables will be needed for 98+ ls1 car rear ends. thirdgen style dont work nor do the LS1 4th gen style

 

Have a question concerning 4th Gen rear axle assy:
Why can't you take the center section from a 4th gen rear and install it in a 3rd gen axle housing using 3rd gen 28 spline axle shafts??? Since all 10-bolt are the same internallly. Anyone want to give the pro & con why it cannot be done??

 

it can be, if its the later 3rd gen 10 bolt that has 28 spline axles.

center section is the same. so you can take out a 4th gen posi and gears, and place it into a thirdgen rear with thirdgen axles.

i never heard it wasnt the same

 

Drum brake rear ends are also a direct bolt in I just swapped a 4th gen rear into my 83 Z with rear drums. My stock lines hooked right up to the 4th gen calipers. The problem you will run into though is the brake lines have a 90 degree bend at the end so you will have to bend them so you can connect them to the caliper lines.