Does anyone know if there was a factory limited slip option in the Ford 7.5" IRS cars? This diff came in cougars and thunderbirds and probably a few others. I believe that a carrier from a solid axle 7.5" will work with the side gears modified/swapped to catch the cv axle retaining clip. I ask because I have an 8.8 and a 7.5 sitting here and would love to use the 7.5 if I can get 3.55 and trac lok for cheap. Otherwise I will regear the 8.8 which already has the factory trac lok. Any guidance is appreciated.
Thanks,
Shav
7.5 clutch kits are obsolete. I used to run the 7.5's all the time when the trac-loks were cheap and easy to rebuild. At this point they aren't really worth messing with when 8.8's are so available.
Will
UltraDork
1/26/21 8:19 p.m.
Yes, it existed, but was rare. I'm not aware of anything other than the MN12 platform NA V6 cars that had it, and it was an option on those cars, not standard. The tag on the diff (assuming it's still there) should say something like "3L27 75" if it's equipped. 327 for the ratio (or whatever it is, may be 3.08, etc), 75 for the ring gear diameter and L is what indicates the Trac-Lok diff. No L in the code, no Trac-Lok.
They did make aftermarket options for the 7.5" IRS that came in the XR4Ti (Sierra) but they were never cheap... and it's still a fragile diff with more than 150hp. If you have a 8.8" sitting there, I can't imagine why you wouldn't use it. LSD setups are cheap and plentiful for them.
There are some ebay kits with gears and a posi for the 7.5 but they come in at about $600 and the differential is not a trac lok style (which I prefer). I should be able to regear and rebuild the 8.8 for less than that so that will likely be the path I choose unless I stumble upon a great deal for 7.5 parts. I only prefer the 7.5 because its a touch smaller, easier to carry around the garage, and would probably have slightly less parasitic loss.
I checked all the thunderbirds/cougars at the local yard and all the 7.5s were open. I've never heard of the 7.5 IRS being fragile, thats interesting feedback. Most of what I have heard about them is from the v8 miata guys claiming they are unbreakable. Thanks for the responses.
gumby (Forum Supporter) said:
7.5 clutch kits are obsolete. I used to run the 7.5's all the time when the trac-loks were cheap and easy to rebuild. At this point they aren't really worth messing with when 8.8's are so available.
Somehow I remember modifying the ears on an 8.8 clutch kit to work in a 7.5.
Might have misremembered the exact issue I was facing.
Saron81 said:
They did make aftermarket options for the 7.5" IRS that came in the XR4Ti (Sierra) but they were never cheap... and it's still a fragile diff with more than 150hp. If you have a 8.8" sitting there, I can't imagine why you wouldn't use it. LSD setups are cheap and plentiful for them.
The XR4Ti/Sierra diff isn't related to the American 7.5, is it?
if it IS.... There is a way to use a Chevy differential in the XR4Ti rearend. It requires modifying the case so you can wedge the thing in there due to the way the Sierra's rearend is designed.
