915 output flanges - please help me set this up for my 915 swap

cowtown · 07-16-2004, 07:59 PM

I'm replacing an early '75 915 (915/40) with a later transmission (915/62). The output flanges on the old trans. are the 4-bolt M10 coarse spline type. The CVs measure 110mm.

The outputs on the new 915/62 are 6-bolt, 100mm, fine spine.

So my quesition is, how do I make this work? Should I replace the entire CV->axle->CV->wheel hub stub assembly? If I do this, can I use my existing wheel hubs with new, later axles?

Or, can I just get two new 100mm, 6-bolt CVs, and mount them on the transmission side to my old axles and bolt them up to the 6-bolt transmission output flanges?

Any help very much appreciated. I can't wait to get back on the road. I've been driving a '91 Jeep for 6 weeks!

jpnovak · 07-17-2004, 04:06 AM

You should be able to use the correct CV for the hub side, the correct CV for the 915 side and install them on one axle. The other option is to swap hubs on the trailing arm. HMM you can't do that with the 930 transmission. The hub width is too wide.

Jim Smolka · 07-17-2004, 04:11 AM

Could you use the o/p flanges from the old gear box and put then onto your new gear box?

cowtown · 07-17-2004, 07:20 AM

Thanks for the replies.

I can't use the old output flanges because they are coarse spline and don't fit into the diff. of the new transmission.

I'll try getting two new 100mm 6-bolt CVs, one for each axle at the transmission side, first.

If I end up having to get new axles and stubs, does anyone know if the stubs that go through the wheel hubs are all the same for the 915 cars? Or are there fine and coarse spline to worry about there too?

Henry Schmidt · Henry Schmidt's Garage

The way to cure this problem is to buy 930 transmission output flanges. They are 6 bolt but they are 10 mm like your CVs. Now you just machine two of the holes on the flanges to fit the pins on your CVs.
That's it. What you will have is a 4 bolt flange with fine splines. to fit your late 915.
We have both stock 930 flanges and flanges modified for this conversion in stock. 930 flanges are not cheap but this is your best fix.

hahnmgh63 · 07-17-2004, 06:05 PM

Colin, I'm interested in the Route you go as I'm in the same boat. I am dropping a 3.6ltr with a later 915 in my '74 which had the 4 bolt flanges. I figured a 6 bolt flange stub axle would interchange but I don't know for sure. Hopefully somebody will reply to this. Then I would need the stub axles and the axles with CV's that go with the newer transmission that I am shopping for. MGH

cowtown · 07-17-2004, 06:17 PM

Quote:

Originally posted by hahnmgh63
I figured a 6 bolt flange stub axle would interchange but I don't know for sure...Then I would need the stub axles and the axles with CV's that go with the newer transmission that I am shopping for. MGH

MGH, we'll know the answer to this question soon - Tuesday or Wednesday. I ordered a used set of SC axles today. They will have 6-bolt, 100mm CVs as used on the later 915.

This happened before I saw Henry's post, which sounds like a great (maybe the best) solution.

Anyway, I'll be fitting these SC axles to my existing wheel hubs, so we'll see about the stub axle question.

It's amazing that there isn't more information on the forum about this, as I know there are quite a few similar conversions out there. I've searched and searched, but I haven't found a definitive answer about the stub axles yet.

hahnmgh63 · 07-17-2004, 06:26 PM

Colin, did you get 6 bolt stub axles with the SC axles? MGH

cowtown · 07-17-2004, 06:44 PM

Yes, new 6-bolt stubs.

cowtown · 07-20-2004, 09:07 PM

Quote:

Originally posted by hahnmgh63
Colin, I'm interested in the Route you go as I'm in the same boat. I am dropping a 3.6ltr with a later 915 in my '74 which had the 4 bolt flanges. I figured a 6 bolt flange stub axle would interchange but I don't know for sure. Hopefully somebody will reply to this. Then I would need the stub axles and the axles with CV's that go with the newer transmission that I am shopping for. MGH

hahnmgh63, here is the followup - the new 6-bolt SC axles and stubs (bottom) appear to work with my early '75 wheel hubs just fine. The stub axle splines slide right in to the early hub.

The 100mm-diameter CVs are a bit thicker than the 110 mm CVs (top), but overall length of the axle-stub assembly is identical

Randy Webb · 07-20-2004, 09:47 PM

Stub axles (aka joint flange) -- P/N's from PET:
1969 -- 901.332.209.10 -- "Loebro" -- MG 3; SG 5; Illus. 305-00
1969 -- 901.332.209.12 -- "Loebro" -- MG 3; SG 5; Illus. 305-00 (2nd
page)
1971 -- 901.332.209.15 "Loebro for chilled cast"
1971 -- 901.332.209.21 "Loebro for pressure casting"
1973 -- 901.332.209.15 "Loebro for chilled cast"

hahnmgh63 · 07-22-2004, 08:55 PM

Colin, are the SC axles slightly shorter to make up for the thicker CV Joints? If the joints are 10mm thicker, together that would be almost 1" longer than the old ones(10mmx2). Thanks, MGH

Henry Schmidt · Henry Schmidt's Garage

Come on guys
If you use 930 out put flanges (easily modified), the stock, early CVs and axles fit and you get the larger, stronger CVs. Better and more cost effective and no calculations as to fitment.
The rest of this exercise seems somewhat futile.

cowtown · 07:25 AM

Quote:

Originally posted by hahnmgh63
Colin, are the SC axles slightly shorter to make up for the thicker CV Joints? If the joints are 10mm thicker, together that would be almost 1" longer than the old ones(10mmx2). Thanks, MGH

MGH, I lined up the new and old CV/axle/output stub assemblies side-by-side, then compressed the CVs to remove their slack, then confirmed that the entire assemblies have the same length. There might be a 2-3mm difference, but no more than that. Since the stub axles are identical in length, I would say the axles themselves must be shorter, but I did not measure the axles by themselves.

Quote:

Originally posted by Henry Schmidt
Come on guys
If you use 930 out put flanges (easily modified), the stock, early CVs and axles fit and you get the larger, stronger CVs. Better and more cost effective and no calculations as to fitment.
The rest of this exercise seems somewhat futile.

Henry I agree, your solution would be better, and I'll use it if I run into problems with these SC CVs.

If the 110mm CVs are indeed stronger then the 100mm CVs, I wonder why Porsche downgraded this part?

This is a more trivial point, but there's something to be said for getting the 6-bolt units from a maintenance perspective - those smaller bolts are so much easier to torque, and the axles is so much easier to remove without dealing with the two rollpins.

Henry Schmidt · Henry Schmidt's Garage

Quote:

If the 110mm CVs are indeed stronger then the 100mm CVs, I wonder why Porsche downgraded this part?

This is a more trivial point, but there's something to be said for getting the 6-bolt units from a maintenance perspective - those smaller bolts are so much easier to torque, and the axles is so much easier to remove without dealing with the two rollpins.

Porsche is a small company that quite often change parts base on cost. They may have also changed because they thought the larger more expensive CVs were overkill.
You might notice that they went back to the larger CVs on the 930, my guess, they thought they were stronger.

As for ease of maintenance: once every 75k miles ?