posi rear end

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Not to be rude but why do you want posi? You don't have enough power to spin one wheel let alone both. 2.3's with auto's are rather enemic. You would be better off spending money on power. When you get to the point where you keep sending the one wheel up in smoke at will, then get posi. I have a cam, higher compression, sidedrafts, header and exhaust and a 5 speed with 3.55 gears. I still don't feel I need to spend the big $ for a posi. I have an 8" rear which posi is readily available.
 
On Fords it's actually called a Trak-Lok....the easiest way to get something that would swap directly in would be to find the rear axle from an '83-86 Thunderbird Turbo Coupe. It's a 7.5 axle (same as yours) with drums, 3.45 gears and a trak-lok. The gears won't be as good as your stockers though (you have 3.73's).
 
The 8.8 out of a 5.0 car is a bolt for bolt swap, but the main brake line coming from the master cylinder will need to be relocated to the opposite side.

The Turbo coupe rear will work, but I think it's a little bit wider (even the drum brake versions).

Both are probably the easiest to do though. The other way is to get a 7.5 Trak-Lok diff from either the above mentioned Turbo Coupe or Trak-Lok equipped Aerostar, Ranger, Bronco II rear axles and install the setup in your rear axle. It'll require some work and a dial indicator to setup the ring and pinion. I'm doing mine this way because I figure it's a good time to replace bearings, and rebuild the diff I bought so I'll have a fresh rear axle when it's all said and done.
 
Not to be rude but why do you want posi? You don't have enough power to spin one wheel let alone both. 2.3's with auto's are rather enemic. You would be better off spending money on power. When you get to the point where you keep sending the one wheel up in smoke at will, then get posi. I have a cam, higher compression, sidedrafts, header and exhaust and a 5 speed with 3.55 gears. I still don't feel I need to spend the big $ for a posi. I have an 8" rear which posi is readily available.

my car does have enough power to spin one wheel. anytime i want i just light it up its just kind of pathetic to see only one wheel spining and not the other wheel thats why im looking for the posi.
 
originally yes, but anymore it's a universal term for limited slip. It's like saying Q-tip instead of cotton swab.

Don't let the purists know I said it though. They'll make me write Trak-Lok 1000 times on the chalk board. :)
 
To answer the original question, yes, you can put a 7.5 in traction lok differential in your existing case.

You can, as others have said, get a used 7.5 in traction lok unit from a Ranger truck, Aerostar van, Thunderbird turbo coupe, or 82 to 84 Mustang Gt. For the T bird or Mustang, the whole axle assembly a direct bolt in. Many other 79 to 84 Mustangs came with tractionloks, my 82 was an original straight six car and came with a 2.73 tractionlok unit.

I would simply buy a Ford Racing 7.5 in traction lok unit and install it.

Buy the time you get a used one, clean it, buy bearings, shims and seal, you might as well just buy a new one, and an install kit.

I have two Ford Racing 7.5 t/l's that I bought new. One has held up to several hundred strip passes, and a few sprayed launches in my 5.0 toy, so they are tough units.

On the other hand, posi 8.8 axle assemblies from 5.0's are also readily available used, an may be cheaper, when you just buy and install the whole thing, no setup required, unless you want to change gears.

Obviously, the 7.5 and 8.8 posi units and other internal parts do not interchange. The axles will interchange, except that T-bird axles are longer than Mustang axles.
 
Who needs 'trac lock' anyway? :shrug:
I've never had a trac lock in my 2.3 and I've run some quick times. Never was a big deal for me. On my car from a roll, both tires usually spin and I end up sideways, even without trac lock.
A stock 5.0 8.8 will have gears that your 2.3 won't be happy with and it'll add the better part of 100lbs to the total weight. Just something to consider.