Clutch type LSD fluid upgrade - are they picky?

[Wolverine]

The NON-Torsen rear differential in the S550 Mustangs... standard clutch type.. are they picky about fluid viscosity or additives? I know Torsen is the solution, but I’m swapping my 3.73 for a 3.55 for higher speeds in second gear (autocross) and I won’t be rebuilding them to swap my Torsen over at least at this point in time.

Will 75W-140 fluid weight affect clutch engagement/performance? I know wet clutches can sometimes experience issues if the oil is TOO slippery, or the viscosity is far different than stock.

Usage is autocross and daily driving.

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[GregO]

https://www.motul.com/us/en-US/products/gear-competition-75w140
As good as it gets.

 

[abmobil]

Ford calls for 75w85 which I’m pretty sure is fuel economy driven.

I Installed Amsoil Severe Gear 75w110 In my GT at 8400 miles. Now with 9900 miles I have not noticed any strange noises or behavior from the LSD. I did not add any friction modifier.

I imagine Amsoil in the 75w140 flavor would give similar results.

 

[BmacIL]

The NON-Torsen rear differential in the S550 Mustangs... standard clutch type.. are they picky about fluid viscosity or additives? I know Torsen is the solution, but I’m swapping my 3.73 for a 3.55 for higher speeds in second gear (autocross) and I won’t be rebuilding them to swap my Torsen over at least at this point in time.

Will 75W-140 fluid weight affect clutch engagement/performance? I know wet clutches can sometimes experience issues if the oil is TOO slippery, or the viscosity is far different than stock.

Usage is autocross and daily driving.

And I'm looking to swap my 3.31 clutch pack for a 3.73 torsen myself, funny enough.

I put in BG 75W90 oil and it seemed to help with engagement slightly, but in general wasn't a big difference from the factory oil. I know many have used the 75W140 in the clutch packs without issue, and it will hold up to track heat better (though autocross really doesn't get it working that hard).

 

[Wolverine]

I don’t WANT to lose my Torsen. I autocross my car and it works well (enough) for that. It would survive longer than the clutch based diff I recently picked up. However, I’m going to swap complete diffs because in the short term the better gearing of 3.55 will help me more than the loss of Torsen will hurt me, assuming these clutches are in good shape (30k mile takeoff).

After finishing the last few events of this season I may disassemble both and build up a Torsen equipped 3.55 for use next year, and have a clutch packed 3.73 for a spare. Heck I’m still not sure 3.55 is “enough” and I may want to go further to 3.31. Time will tell.

Edit: As for fluid, I am hoping to swap diffs this weekend and don’t have time to order fancy fluid, so it’ll have to be locally sourced. I’ll try to find something in 75W-140 full synthetic, and I expect some might have friction modifier pre-mixed and included and other brands may not. Hopefully I find one WITH it so that’d be one less thing to hunt down.

 

[GregO]

I don’t WANT to lose my Torsen. I autocross my car and it works well (enough) for that. It would survive longer than the clutch based diff I recently picked up. However, I’m going to swap complete diffs because in the short term the better gearing of 3.55 will help me more than the loss of Torsen will hurt me, assuming these clutches are in good shape (30k mile takeoff).

After finishing the last few events of this season I may disassemble both and build up a Torsen equipped 3.55 for use next year, and have a clutch packed 3.73 for a spare. Heck I’m still not sure 3.55 is “enough” and I may want to go further to 3.31. Time will tell.

Edit: As for fluid, I am hoping to swap diffs this weekend and don’t have time to order fancy fluid, so it’ll have to be locally sourced. I’ll try to find something in 75W-140 full synthetic, and I expect some might have friction modifier pre-mixed and included and other brands may not. Hopefully I find one WITH it so that’d be one less thing to hunt down.

Fancy Fluid....
Man you live in Wernher Von Braun's Rocket Town USA, there's got to be a local source for the fancy lube.
Call Cycle Gear over on the parkway, they may have your gear oil flavor. 75W 90 or 140
Honestly though, we run the Motul Gear 75W-140 in Porsche GT3 Cup Cars, It holds the temps down and is hands down a superior fluid.

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