LSD for early vs. late 915

[stownsen914]

I'm rebuilding the 915 from my racecar. Turns out I have what I believe to be an unmarked '73 or '74 case. I understand that the early mag 915s use the same diff as a mag case 901/911, and they're different than the '75-on mag and aluminum 915s.

So will a later 915 LSD fit my trans? I'm putting in an 8:31 R&P as well.
And the Quaife that came out of my trans - I guess it will fit a mag 901/911? And will it fit a '75-on mag or aluminum 915?

Thanks ...

[Mahler9th]

I am sure someone else will chime in. But I think there is likely a dimensional equivalence. Based on the Guard Transmission product listings, I think the only potential issue is the spline pattern (fine or course) that would have to mate up with what you use for output flanges, and their mating to the CV's.

I made the change from the excellent Guard TBD to a Guard LSD a few years ago. Different vehicle dynamics and set up optimization, and some debate in my application regarding lap time potential delta.

I am happy I did it because of some other suspension, tire and set up changes I made at the same time.

I think the factory LSDs are not as optimized as the Guard units in some respects, so instead of rebuilding one of those I had on hand (a later ZF), I sold it and went with a Guard.

And now that my racing plans have changed, I will probably liquidate the excellent like-new Guard TBD (fine spline) I still have on hand.

I think your Quaife situation is similar-- dimensional equivalence is likely, but dropping into a particular 915 might require spline matching.

[eastbay]

This was posted back in the day, might help.

[stownsen914]

Thanks eastbay, that's helpful. Looks like a later 915 LSD will fit my early mag 915 (or a mag 901/911 trans) with a spacer at the ring gear and another under the left (in the diagram) carrier bearing.

I'll have to measure the Quaife that's coming out of this trans and see which one of the above diagrams it matches.

[faapgar]

Hi,I put the QUIAFE in your car many years ago and it should have a shim under the ring gear.I may have some spare shims as I bought 20 QUIAFES for my 1st order.Fred

[Matt Monson]

If you are using an 8:31 ring and pinion you can use either a 915 coarse midyear or a 930 fine spline lsd with no spacer ring.

You only need the spacer ring when you are using a diff designed for an 8:31 with a 8:31 ring and pinion.

PS. Only people who bother to leave a voicemail get called back. Hang ups never get called back. Funny how that works.

[stownsen914]

Fred - I'll check, but I think there was a spacer under one of the carrier bearings but not the ring gear?

Matt - thanks again for that info. I didn't want to make you have to call back, but next time I'll leave a message