Hi guys, I've had a hell of a time trying to beef up my rear end.... question.... all trans am rear ends were 26 spline until like 1988 or around there??? I have an 86 trans am and I've been telling my dad (I'm 25 and active military we're just close haha) that my rear end is positivley a 26 spline and they didn't make 28's in 86.. he thinks i'm wrong. whats the info on this? second question is what should i do with my rearend... buy a 7 1/2 posi unit to put in it or go 8 1/2... I've already bought the ring and pinion and install kit to put the 7 1/2 unit in my car but i just got back to the states and the posi unit i had bought a few months back on ebay is infact an 8 1/2 with the wrong writeup =( I've found a new posi unit that will cost me 200 bucks... OR i found two 2nd gen posi track rearends for 125 each.. i could buy them, change the gear ratio and throw one in my car... only expense with this is the install kit, ring and pinion for gear change and paying someone to cut and reweld brackets on AND 275 for traction bars so i can get around having to use the control arm... My trans am has a 383 built crate motor rated at 453HP and a 350TH tranny what would be my best option? cheaper way out or shelling out more than double for sure to set up the 8 1/2.

the 8.5 carier, parts, gears ect will not fit in the 7.5 case. You will not find a 8.5 case to fit a 3rd gen with the torque arm bracket, and adding one to the case is very difficult.

if the rear you have is stock its 26 spline. but the car is 22 years old, so you never know what has found its way into the car since it was new. Only way to really know for sure is to pull an axle.

as for the better setup for the rear. the 8.5 will cost you more than you think after its been setup for the car. You have to do something for the torque arm mount, thats not something anybody can do, the width of the rear is in question, you may have to have the housing and axles shortened to fit.

best bet would be to save your pennies and pickup a bolt in moser/strange 12 bolt, 9" ford or dana 60. They are specific to the 3rd gen and have the torque arm mounts

I'm positive of whats in the car because i bought it from the original owner (lady that used to cut my hair) back in 99. It was 100% stock at that time.

instead of using the torque arm I would use the lakewood traction bars.

The above advice is correct.

Third gen 10 bolts have 26 spline axles up to the 89 production year. Late in the 89 production, they might have the 90-92 28 spline axles. It's easy to upgrade a 82-89 10 bolt with 90-92 28 spline axles providing you also use a 28 spline carrier.

As mentioned above, your diff upgrades are very limited. Third gens use a torque arm suspension and no other diff is an easy or direct swap. Some people have succeeded in doing foreign diff swaps including Ford 8.8's. Your aftermarket choices for a direct bolt in include a 12 bolt, 9" or Dana 60. None are cheap however the cost of trying to fabricate some other diff to work properly under a third gen may cost more.

The Lakewood traction bars are a poor replacement for the torque arm. They'll work fine for street use but are not a good choice for a performance application. Since you want to replace the diff for performance use, the Lakewood bars are a step backwards.

thanks for the info guys. I'm just going to get the correct posi unit for my rear end and hope it doesn't blow up... Headed to Hawaii in about six months so if it'll hold through then i'll be able to buy a 12 bolt aftermarket when i get back.

that is exactly what I would do. and exactly what I am doing. Except for the hawaii part

be sure not to buy a gov-lock style.