'69 901 transmission axle flanges on a '76 915 ?

[wjdunham]

Hi Pelicans, after much google searching I have not found my answer, so here goes: I'm in the process of putting a 1976 mag case 915 transmission my 1969 911E which was originally equipped with a 5-speed 901 transmission. The car is at my body shop so I can't make any measurements or inspect things.

Can I swap the axle flanges from the 901 (which I assume are the 4-bolt 108mm course spline) on to my 915, and re-use my CV joints/axles as they are now?

If I need new flanges for the transmission, can I use 915 108mm 4-bolt versions and keep my CV/axles - will the axles be the correct length?

There seems to be quite a few variations in this area and I can't piece together the picture from all the threads on this subject.

Thanks for any help,
Bill

[jpnovak]

The differential and flanges are different.

The only way I know to do this is to install the 100mm 6-bolt stub axels into your trailing arms. They should be a direct swap. Then use the 100mm 6 bolt 915 half shafts and matching CV joints.

That is what I did years ago on my 71 that ran a later 915.

[wjdunham]

Originally Posted by jpnovak

The differential and flanges are different.

The only way I know to do this is to install the 100mm 6-bolt stub axels into your trailing arms. They should be a direct swap. Then use the 100mm 6 bolt 915 half shafts and matching CV joints.

That is what I did years ago on my 71 that ran a later 915.

Shoot - I just sold my pair of 100mm 6 bolt stubs from the transmission. Is there a way I can use a pair of 915 108mm 4-bolt versions? - is there an axle that will work with the 108mm 4 bolt versions already on my half-shafts and transmission?
Bill

[wjdunham]

Here are my two choices for the transmission side flanges - both are the same height and fit the 915 tranny, only the CV mount is different. Prefer to use the 4-bolt version on the left if possible (since I don't have the ones on the right any more).

[wjdunham]

Been doing some more reading. This thread has lots of good info.
CV and Axle Cross Reference

According to what is in that thread, I should be fine using the 4-bolt transmission flange with my current 1969 axles. The overall length of the axle + CV joints remained the same from 69 - 75.5. On the later versions the CV joints were 8mm thinner and the axles longer to compensate, but looks like the overall dimension between the transmission flange and the outer axle stub is constant.

Regardless of the the transmission (901 in my 1969, or 911 in the later models) - the axle assemblies appear to be constant length. Am I correct on this?

Bill

[Matt Monson]

Yes, it will work. The mag case 911 and 914 gearboxes use the same differential as a 72-74 915 w/7:31 ring and pinion. What changed on the midyear 915s was the ring gear offset for 8:31. They all use the coarse spline flanges on the diff side.

I used to have a 1970 gearbox in my 75 targa. Just used the original axle assemblies through the flanges.

[wjdunham]

Originally Posted by Matt Monson

Yes, it will work. The mag case 911 and 914 gearboxes use the same differential as a 72-74 915 w/7:31 ring and pinion. What changed on the midyear 915s was the ring gear offset for 8:31. They all use the coarse spline flanges on the diff side.

I used to have a 1970 gearbox in my 75 targa. Just used the original axle assemblies through the flanges.

Thanks Matt, very helpful. One less thing to worry about.
I'm also upgrading the trailing arms from the fabricated steel ones to the later aluminum. Can I reuse the outboard stub axles in the aluminum arms?

Bill

[Matt Monson]

Yes.