Hey everyone,i'm not on the thirdgen too often. i own a 2nd gen 79 TA.a good friend of mine has a base model 85 firebird with a 6cyl.I'm just curious, i have the 10 bolt rear end out of my car, a TH350, and an oldsmobile 455 that we'd like to swap into the thirdgen.would it fit? i udnerstand it isnt leaf spring in the rear as in my car is, but any suggestions at what kind of project this would be would be helpful.thanks

It won't be a simple swap. Check the Pontiac swap sticky at the top of the forum.

okay cool, im reading into it. looks like the motor mounts are out there for it.. gotta do the engine wiring myself, which is simple on these motors.we'll probably be going with some high-flow manifolds for now. and a remote oil filter locater. how about the computer? would i just rip the computer out and just re-wire the gauges and everything too? cause i know the speed-o goes to the th350, tach to the distributor, and then just the oil and temp gauges. this car just has dummy lights. which is annoying to me.

The transmission because of the different bellhousing bolt pattern will also need to be swapped. A TH350 will work with a different or modified crossmember. The second gen diff won't fit because third gen diffs use a torque arm and there's no way to easily mount the torque arm onto any other diff other than another third gen or a fourth gen diff.

well i already have the TH350 for the engine. then my best bet would be to just find a rear end from a GTA or something?

A 9 bolt from a GTA or IROC that came with a L98 is a little bit stronger than the 10 bolt, but not by much. There are no cheap options for a strong diff in a third gen.

An 85 Firebird has a mechanical speedometer, so there's no problem there.

I replied to your PM; hope that info helps.

I think you are better off with a 700R4 for a V8 third gen and a bellhousing adapter to your olds engine, but that is just my opinion. The money you will SAVE by not modding or buying a crossmember for the torque arm will offset when you do buy a V8 700R4. Plus, you'll have a deep first gear and overdrive.

The rear is, as stated above, a pricey prospect no matter what. If you run a factory rear, you will need aftermarket axle shafts at a minimum (be sure to get 28 spline units, not 26) and then there is still no guarantee that your rear will last. On a budget, sometimes it is cheapest to buy the aftermarket (housing only) 9 inch ford piece and then scrounge the junkyards for a center section from a 70's 1/2 ton ford pickup. Count the splines, and then order your axle shafts to match.

Just throwing that stuff out there because it sounds like you are on a budget.