Diffs.. What to do?

[spookypt]

I'm no officianado but pretty sure the E28 M5,E24 M6 & E23 735i are large case diffs with 210mm r&p and I know for certain will not bolt into the mid case diff cradle.

[Tom Wells]

spookypt,

I'm going through this on a 2003 Mustang Cobra IRS in a (drum roll) 1981 Mercury Zephyr station wagon with a 557 that is intended for open track use.

After reading a bunch about problems on the track with overheating I concluded it needs an oil cooler which I'm in the process of installing. At the same time, I've installed the newly available Ford differential cover: 1999-2004 COBRA IRS AXLE GIRDLE COVER | Part Details for M-4033-G3 | Ford Racing Performance Parts

It has two major upgrades: first, it's waaaay stronger and has diff bearing support caps, and not surprisingly it has all the holes needed to add an oil cooler.

Here's a sample of how some correct the problem (I think this one is pre-new-cover): IRS Differential Cooler:

In your shoes, I might try a cooler first, then if another failure occurs, go to the Ford IRS diff. Don't scrimp on the size of the cooler.

One theory is that the straight axle holds more fluid and has much greater cooling area if you include the axle tubes.

The IRS is kind of shrouded and has only the flexy aluminum diff to get rid of heat. The track guys say the least that happens is that the diff fluid boils and then the limited slip gets cooked. Don't know what might happen after that...

My Cobra has a Jag rear, a very large cast iron chunk with inboard disk brakes and has survived many 30 minute track sessions just fine. Newer is not always better!

Just stuff to think about,

Tom

[Jac Mac]

One of my fellow GT40s members 'GT Bob' posted this compare pic of the BMW units.... but what you 'really' need is a housing which allows 9" heads, few outfits have/do make em in OZ & USA, but not in large numbers hence price is high, I built one, but don't do them on a commercial basis, I simply don't have the time.
With regard to a cooler I could understand that a 'clutch' type LSD might be warrant them due to the heat buildup, but with tru trac or other detroit lockers some means of feeding oil to the R&P contact area is probably more beneficial, but that's more of a driver call as to which unit he prefers.
Other factor that comes into play is the amount of hypoid offset, Ford 8.8 has similar to the BMW unit, 9" has about 0.75" more which can be handy if you want to get overall car height down.

[spookypt]

Thanks JacMac. Very interesting pics. My Mid Case has a different set up to that with a large bolt holding the pinion end to the cradle as per pics below rather than that bolt on bracket assembly.

I also run a cooler so have that issue , if any exists, covered.