915 tranny Options

[john914somers]

So I'm starting to change my 3.2/901 914 race car into a 3.6/915 and I am wondering if an older magnesium case 915 with a 7/31 ring and pinion will hold up? Any opinions are greatly appreciated! Thanks a ton!!!

[pcar916]

Why is first gear a problem? It's not cantilevered like the 901/914 first gear. In addition...

The mag-case 915's have steel inserts for the bearings to press into, and the addition of a one-piece bearing retainer is the fix for any flex that might happen between the two bearings. The later aluminum cases don't have the steel bosses and are supposedly weaker there. Plus the mag-cases are a little lighter.

The other required piece, and more important in my opinion, is the replacement of the side cover with either a late-model one with stronger webbing, or a billet piece. That's a real weakness in those boxes because they allow the R&P mesh (therefore the backlash/ R&P tooth-contact pattern) to change with the input torque. That's independent of the 7:31 ratio. I think that's good on an autocross course for sure, and tight technical tracks.

I'm still using the 914 transaxle (also 7:31) with my 993 engine, and until I get some more time I'm waiting to put my mag-case, 7:31 into my car as well. I have a later ('84) 915 I could use, but it's heavier and I don't see the need (except for better gas mileage perhaps) to use it yet.

Good luck