The actual carrier units and thier rebuild kits are the same for both the solid axle and irs differentials. Even the differential rebuild kit (bearings, crush sleave, gasket, etc) are the same. The only difference is that you have to pick up the side bearings and axle seals seperatly since a solid axle does not have them.
BTW, this was really the main disadvantage I found with the 7.5. Since Ford dropped it and basicly disowned it they now offer no support what so ever for it. What that means is while you can still buy factory parts fairly inexpensively for the 8.8 everything for the 7.5 must come from the aftermarket. A complete new tractionloc carrier unit for an 8.8 is right around $200 as was the 7.5 version until a few years ago. Now you can still buy a new unit for a 7.5 but only from Yukon for around $400. The rebuild kits are the same story. The 8.8 clutch packs are half the price of the 7.5 version with less components from the aftermarket.
If I was starting from scratch I'd go with an 8.8 and deal with the less exhaust room. With the carrier unit I chose I shouldn't ever have to go back in and rebuild it once its set up assuming I keep after the oil (I had a drain plug installed for quick oil changes). Clutch packs wear and need replaced. I would not want to look for those parts for a 7.5 another 5 years from now.

-Jason

 

Thanks, that's what I figured but could not find confirmation. Yeah, sucks that Ford abandoned the 7.5, especially considering the amount of them on the road. I see there is a tuetrac diff available and may go that route down the road, just don't have the funds now. I have a 3.27 LSD, and figure if I rebuild it and stack it tight (similar to the performance 8.8 method), I have get a good amount of use out of it.

 

I do think that a 7.5 is fine for any Ford V8 Miata. However, keep in mind that if you are going to push it hard with the TractionLoc you may run into the same overheating issues I had, expecially with a fresh set of clutch packs. The overheating has nothing to do with the strength or capability of the 7.5; the issue is the oil capacity which is less than half of that of an 8.8. V8 builders back in the day (When Fords ruled and Rover V8 builders were the minority group amoung us) ran into this issue as well and would run 6' long tubes on the diff breathers to handle it. Some even had catch cans hooked up in the trunk to keep the boil over off the road.
I'm banking on the relatively friction-less mechanism of the TrueTrack to be substantially cooler running than the TractionLoc's clutch packs. The research I'vd done as well as my rear end guy's experience shows I should be ok.
The funny thing is quite a few people have been fine with the 7.5/TractionLoc combo, even on the track. One customer of ours road raced his for four years without a drop boiling over. The only reason for this I can fathom is that his clutch packs were actually worn to the point where they were not creating the heat mine were. On a side note, my rear end guy checked how much life was left in the old unit when he took it out. It was only operating at 30% or so.
-Jason

 

In my 2000 Cobra "R" I hooked up a smaller cooler with an electric fan in the trunk to keep the aluminum diff from melting

 

Well, voodoo has been applied

With the A trim it made 420/420 at 8lbs. Dyno'd it again this week with the S trim at 11 lbs and it made considerably more.....

I've been playing with it on the street and it
Lays the power down VERY well with a couple little tricks......

So far so good on the 7.5 rear........fingers crossed....

 

I just tore apart the trac lok unit yesterday and it is toast. I had no problem getting the side gears to spin like an open diff would by hand. Ordered a new set of clutches and will pack it tight (similar to mustang 8.8 trick). We'll see. Not planning on tracking the car much, most of it's life will be street driving so we'll see how things hold up. If I run in to heat issues, the torsen diff will be on my shopping list as it's cheaper than a diff cooler.

 

Update.....

2 months of driving the car hard at between 400-460 rwhp. The 7.5 rear end and axles are holding up fine.

I did develop a vibration that was pretty nasty over ~70-75mph.

Just like papa bear said was likely to happen.....U Joint had begun to fail!

I don't know how old the u-joints were that were in it......I replaced the U-joints with new non-serviceable units and had the driveshaft balanced and problem solved!

 

Glad to hear it's working out for you. And you throw enough power at a car your going to find the weak links. Car sounds like a really nice build.

 

I've been an avid drag racer for many years and have learned the weak links in the fox body drivetrain up to 1000whp. I'm having to learn the ropes in the IRS rears......so far, I'm relatively impressed with the little 7.5.