915 flange problem

[jhelgesen]

Hey guys, I just put the new seals in my 915 tranny to go with the 3.0. My car is a 912e that had a 923 tranny. I sold the 923 to get a 915 that came with the 3.0. Anyway, the 915 did not come with output flanges, so I kept the ones from the 923, along with the bolts. I just put the flanges in and when I tightened the bolts, the dif locked up. If I take the bolts back out and tap the flanges out a hair, its back to normal.

What gives? Wrong flanges? Wrong bolts?

Help help help cause the engine is going in tomorrow.

Thanks!

[jhelgesen]

Hmmmm, looked up part numbers between the 76 923 tranny and the 79 915. Both use flange 923.332.209.2 and bolt 901.332.275.12. The only thing different is the 79 leaves out the washer. Guess I'll take out the washer and see what happens.

[jhelgesen]

Problem solved!!! Thanks to Rob bringing a spare set of flanges to the install today we found out what the difference between 923 flanges and 915 are. 923 are course thread, 915 are fine thread. We think the 923's are different because they were used with the 7:31 r&p.

So now I need to replace the 915 flanges that Rob loaned me. Anyone got a spare set for sale or want to trade for the 923's?

Thanks

[Grady Clay]

John,

Look carefully at both transmissions and flanges. A LSD has different flanges and one way of incorrect parts left it locked up and the other way too loose. As I recall, when in the too-loose situation, the thread piece could run into the differential shafts in a LSD or the retaining block in a standard differential with unpleasent results.
I think the 915 and 923 had the same differential housing so I don't see how the different R&P ratios would effect this issue.
Do you still have the 923? If so, compare the distance across the transmission of the two axle flanges to a known 915 and to your new set-up. Measure the float (end-play) of all the flanges.
The good news is that one may be a LSD. For the cost of an O-ring, pull the side cover and look.

Best,
Grady