Hey all, just curious about a few things regarding rear end swaps/upgrades. Currently have a 1979 mustang with a 7.5 open diff with 3.45 gears. On one hand I'd like to upgrade that rear end to a posi with 3.45 or 3.73's, keeping the car "numbers matching" if I ever sell it. On the other hand, I'd have to assume it would be easier or possibly cheaper to just throw a complete 8.8 or even another 7.5 already done into it. I can swap a rear end myself but I'm hesitant on rebuilding one. I also doubt this car will ever get more than 300 HP. So I guess the main question here is what do you guys suggest the best route to be? Looking more for ease of building/finding parts than anything.
Easiest 8.8 swap for '79
- Thread starter Kulvox
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My opinion, try to find an 8.8 from another Fox. In the 90s I had an 87 Ranger STX, 2.8 4x4. It had the 7.5 and it broke under normal driving conditions. I had it rebuilt and it never gave me any issues, but it still left a mark on my soul! 
An 8.8 can withstand a lot more, from my understanding, than a 7.5 can. So, even if you don't think you'll ever get more than 300hp, you may change your mind someday - the 8.8 will definitely hold up to whatever you throw at it. The 7.5..... it's questionable. Just my opinion and experience with the one 7.5 rear I've had.
An 8.8 can withstand a lot more, from my understanding, than a 7.5 can. So, even if you don't think you'll ever get more than 300hp, you may change your mind someday - the 8.8 will definitely hold up to whatever you throw at it. The 7.5..... it's questionable. Just my opinion and experience with the one 7.5 rear I've had.
Stuff your original rear in a corner and buy an 86-93 8.8 rear from a Mustang and swap it in.
Only 8.8's 1994 and newer will be 5 lug.
They will also be wider and have disc brakes.
5 lug is an option, one you should probably consider, but if you use an 86-93 it will be 4 lug.
You may want to also consider going rear 4 lug discs at the same time.
They will also be wider and have disc brakes.
5 lug is an option, one you should probably consider, but if you use an 86-93 it will be 4 lug.
You may want to also consider going rear 4 lug discs at the same time.
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Things to consider:
Disc brake 5 lug 8.8 rear ends are wider, makes wheel selection tricky
Since you are swapping the rear anyway you should up date to disc brakes even if staying 4 lug. Not a large selection of 4 lug wheels.
You also have the option of 5 lug drum brakes for the rear.
Check out the tech threads for swap options.
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Disc brake 5 lug 8.8 rear ends are wider, makes wheel selection tricky
Since you are swapping the rear anyway you should up date to disc brakes even if staying 4 lug. Not a large selection of 4 lug wheels.
You also have the option of 5 lug drum brakes for the rear.
Check out the tech threads for swap options.
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- Mar 2, 2015
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I think the brake line has to be moved when swapping in the 8.8 from a fox mustang. If I recall the 8.8 line comes down on the drivers side and the 7.5 comes down on the passenger side. It is a direct bolt on though. Upper control arms, lower control arms, and shocks bolt up the same. I don't think your car has a provision for quad shocks. If you use aftermarket lower control arms you wont have an issue without them. I think your year came factory with traction bars that would catch the lower arms when accelerating. That's how my wife's 82 was.
I think them factory traction bars are getting hard to find but good aftermarket lowers and you're 
(I could have said 'scratch'n out, get'n rubber or any of the other sayings that annoy someone here) in no time!
(I could have said 'scratch'n out, get'n rubber or any of the other sayings that annoy someone here) in no time!
My 79 5.0 badged 302 LX (or GLX?) had no such traction contraptions. I put in the limited slip diff in the 7.5 case. I never worried about it because I knew the SROD or street tires would break first.
I would get an 8.8 if I was doing it today. They are much less expensive now.
I would get an 8.8 if I was doing it today. They are much less expensive now.
Almost any Mustang 8.8 will bolt in. I have had both 7,5 and 8.8 axles in my 82. The same axles, four or five lug fit both rears, as long as they are 27 spline. I pull the cover, pull the cross pin bolt, cross pin and c clips, and remove the axles. Then the brakes including the backing plates can be unbolted and hung by coat hangers ,with the brake lines and such attached. The ebrake stuff can also stay attached. Then pull the housing and put in the new one. Then reinstall the brakes, axles, cover, and fill. Lately, traction lock 7.5 units are hard to find, so an 8.8 may be easier to find and use.
Notes Check the location of the axle vent/brake line bracket relative to the brake lines to ensure the one in the car fits the new rear housing and locates the same way.
I have added a 5/8 spacer to the original and the Ford FRPP alum driveshaft to get good yoke engagement in my C4. You may not have this problem.
That said, my 82 has run 1.7 sixty foots on drag radials with is 4.10 7.5 axle.....
Notes Check the location of the axle vent/brake line bracket relative to the brake lines to ensure the one in the car fits the new rear housing and locates the same way.
I have added a 5/8 spacer to the original and the Ford FRPP alum driveshaft to get good yoke engagement in my C4. You may not have this problem.
That said, my 82 has run 1.7 sixty foots on drag radials with is 4.10 7.5 axle.....
