73 7:31 915 r&p in an 85 915?

[fastbacker]

Pretty sure this is a straight swap but need to know 100% for sure.

Thanks-
Craig Backer

[2.7RACER]

Craig,
I put a '72 915 transaxle in my '76 a couple months ago.
Two things.
One the bell housing will need to be notched for the flywheel sensors.
Two the '72 uses a mechanical take-off for the speedo. Your '85 has a sensor and wire to feed the electric speedo.
You could change the speedo to a earlier mechanical model.
Of course you'll need to run a cable for the mech. speedo.
The clutch cable for the earlier models don't use the "U" shaped, (really omega) helper spring.
You may need to rig up something to hold the clutch cable.
The output flanges were different from '72 to '76.
I just exchanged the flanges from my other 915.
Other than the above bolts right in.
My question to you is, Why change?

[fastbacker]

What I was asking is whether the ring and pinions were a straight swap between a 73 and an 85.

Thanks-
Craig Backer

[Jim Williams]

Craig,

I think that mechanically, the parts from a 7:31 will fit into the later 915, but per a recent thread on R&Ps for the 915, there is a fairly involved adjustment process which should be followed to adjust the close tolerances, like pinion depth and ring gear backlash anytime you remove and replace a R&P with different parts. Check out a thread
915 R&P Whine - How do you get rid of (fix) this??

There may be some issues with the CV joint flanges that I'm not aware of, possibly others.

[2.7RACER]

Craig,
I considered a R&P change and decided the smarter move was a complete transaxle swap.
Bought a known recently rebuilt 915 for $1500.
Installed it myself in one day.
Now I have a good 915 sitting on the shelf worth at least $1,000.
Replace the R&P is all labor, plus $500 for the R&P.
Spend the $500 plus close to $1,000 labor.
Didn't work for me.

[beamonk]

There may be differences in the stub axle splines if you swap out the R/P.

[Geary]

Installing the early ring gear will require the use of a 3.0mm spacer (beneath the ring gear), and reshimming for identical backlash. The original diff and flanges are used.