Fox T-Bird/Cougar Forums  

Chuck, I'm not trying to argue, just trying to gain clarity;

If the Fox Mustang 8.8 housing is identical in length to the TC (1988 in this instance, for both rears) rear, then why wouldn't Sport backing plates and SN95 axles work? Or Am I missing something else?

I know the axles themselves (Fox Stang vs Tbird) are different lengths, but that chart does say the 8.8 housings are same length...?

I AM aware that the 7.5 is no bueno, however.

I'm not asking to be spoonfed, but I don't seem to see were the issue lies with the Mustang 8.8 as compared to the TC 8.8, but I might be missing something painfully obvious..

I just finished something almost similar.  I've got an 88 housing, with an 88 sport 7.5 lsd, 98 V6 Mustang axles, 10" T-bird drums drilled to the 5-lug pattern and since the stem of the Mustang axle expands from 1.4 to 1.59" just outboard of the bearings, I had to find different axle seals which apparently fit a 63 Fiat.  For some reason I expected Ranger left axles to fit, and then I expected 94-98 Mustang axles to just fit.  Thank goodness I can navigate seal spec catalogs.

Of course the 94-98 Mustang axles (or the Ranger axles) didn't fit properly. The 86-88 7.5 housing is 3/4" wider (per side) than what those axles are spec'ed for.  The axles are the same length, but as you found out, the bearing surfaces are not in the same location. The 94-98 Mustang axles are a drop-in on the 83-85 7.5 housing and the 87-88TC 8.8 housing.

Cougar/T-Bird 7.5"
Beginning with the 1983 model year, the Cougar and Thunderbird shared a common-width 7.5" rear axle housing with the Mustang/Capri. Therefore, all 4 cars have the same rear end housing, but the Cougar/T-Bird had longer axle shafts. Most Cougars had the 2.73 open-end gear (non-locking). The 1984-86 XR7's had the locking rear with Quad shocks and a 3.45 gear. [COLOR="#FF0000"]This Mustang/Capri style rear end was used until part way through the 1985 model year (approx. 11/84), when the Cougar/T-Bird got a unique width axle housing. It was approximately 1" wider than the Mustang housing and about 1" narrower than a Mark VII rear axle housing. However, due to a different offset rear drum, the overall width was the same (thus keeping the same rear track dimensions). This configuration was used until 1988 on all Cougars and Thunderbirds.[/COLOR] Again, most were equipped with the non-locking 2.73 unit. However, on some models it was possible to order a 7.5" rear with a 3.08 gear for towing. Almost all 7.5" rear ends had the 9" rear drum brakes, which have a finned side profile. Some had the optional 10" drums, noted by their smooth side profile, which came later cars (primarily 1988) with the optional towing package or heavy duty suspension package.

- See more at: http://www.coolcats.net/general/axleinfo.html#sthash.BPNgVscj.dpuf