915 gearbox to SWB

[Seppo]

Hello

I planing to put a 915 gearbox in a 1968 SWB.
How do you solve the half shafts?
Mine is 6xM8 bolts but the 915 is 4xM10?
Or are there some easy solution?

Thanks

Seppo

[quattrorunner]

Just look for stub axles that match what you need. There are fine and course sine stubs you just need to determine what your 915 diff is and then mix n match whatever half shafts work with your car and the 915. As an example, my 930 uses the fine spline same diameter stub size as a 915. I could use the original half shafts of my car. Take your 915 stubs out and have a look.

[spuggy]

Originally Posted by quattrorunner

JAs an example, my 930 uses the fine spline same diameter stub size as a 915. I could use the original half shafts of my car. Take your 915 stubs out and have a look.

Really? Huh. I was sure 930 stubs were originally (hey, you can change anything if you really want) 6 x M10 & 108mm flanges. Or do you have an original SBH and they're different? Dunno much about those...


To the OP, this is a complicated subject, and if you don't do it right, many have found the CV joints won't stay reliably bolted to the flanges. At the very best, this'll probably mean you won't go anywhere at some point. At worst, it could be very bad...

This is a very long thread - but it's pure gold, worth reading it all: Reconstructing Constant Velocity (CV) Joints

Here's an attempt at some Clif Notes. Double-check the information.

Early cars used 108mm flanges with 4x M10 and 2 pins, coarse spline diff/stubs - with stub axles in the wheels to match.

In 1972, the axles got thinner/lighter, CVs got shorter (and so did the attaching bolts), and the gearbox output stub also changed. There's a tech note on one of the very long threads. Older axles/CVs went NLA as replacements - but many well-maintained ones are still in-use...

By 1974, gearbox output stubs had changed to 6xM8 100mm [Edit: fine spline 1978-up per MM)

The 100mm CVs are from the 912E and are generally regarded as somewhat marginal for a 911 in hard use - and especially cause issues if not assembled correctly. Some apparently weren't from the factory, as the bean-counters dropped the schnoor washers and moon plates for a while without telling the engineers... The factory torque rating for the M8 bolts is also close to the elastic limit for a 12.9 bolt - and Bentley apparently mis-quoted this as a higher rating in some editions than it should have been...

Here's a thread from a guy trying to fit an older 915 into a 1974 that has some good info regarding axles/CVs in the discussion: CV Joint and Axle/Half Shaft Compatibility. He ends up fitting G50 CVs to the gearbox end of his 74 axles to adapt them to the 108mm output flanges.

In the second half of MY 1985, 915's switched to fine spline stubs with 6 x M10 bolts with 108mm flanges (change announced 09/84, but was "not for early US production"). I believe that the same axles were used with the G50 up through 1989.

So. 915 108mm fine-spline stubs with 6 x M10 bolts are hard to find as a) prized by folks with high-output motors / driving them hard and b) only made for a short time. Factory ones have been NLA for a long time, aftermarket available. You can also apparently machine G50 stubs to fit in a 915 (several sets were in For Sale recently).

Pretty sure you can remove the pins from the early 108mm flanges, thread them for M10, remove the wheel stub axles and use the late G50 axle with the attached stub. I know this works for a 70's car when going G50, because that's what we did - but I've never owned a 60's car, so don't know for sure what stubs they used in the wheel. My wrench thinks they're the all same and he's forgotten more than I'll ever know - but that opinion and $5 will get you a latte...

One concern Grady (RIP) had was that some early/coarse spline 108mm flanges didn't have clearance for the G50-style end cap. This can be simply omitted.

This thread has some great information; read it all, as corrections/updates posted as it goes on: CV and Axle Cross Reference

According to that thread, SWB 65-68 used a very different setup to '69 and up (6 bolt 94mm flange and much shorter axles) - but it looks like the CV's from the 75.5-85.5 cars may fit your early axles, although they're probably a lot shorter...

[quattrorunner]

Originally Posted by spuggy

Really? Huh. I was sure 930 stubs were originally (hey, you can change anything if you really want) 6 x M10 & 108mm flanges. Or do you have an original SBH and they're different? Dunno much about those...
.

. ...

Sorry if my post was misleading or hard to follow.
I used the 915 stub axles in the sbh 930 box initially to be able to keep the 915 half shafts I already had. So you’re right.
I was trying to show that he can use different combos in order to come up with what he needed. I have no idea what was used in 67 or even any other years earlier than my 76 my car.
The 100mm m8 bolts flanges fit na cars and the fine spline stubs from a 915 fit a 930 gearbox.
His request is for a 915 though. My post is to have him look at his flanges and see what they are. Then he can start the search. But spuggys post comes with lots of info and good threads that could go a long way to answer many questions without getting dirty. Nice

[spuggy]

Originally Posted by quattrorunner

Sorry if my post was misleading or hard to follow.
I used the 915 stub axles in the sbh 930 box initially to be able to keep the 915 half shafts I already had.

Ah, thanks for clarifying. I think I'd have been inclined to remove the wheel stub axles, keep the 108mm 930 flanges and fit G50 axles (you kept the 911 bananas, right? should bolt straight in, if so).

But then I'd already knocked out a set of CVs, had issues with bolts shearing and needing frequent checking etc, so was getting pretty tired of the 75-85 911 axles and glad to see them go.

G50 axles are basically 930 axles (and CVs) for 911 banana arms. Everything much heavier duty. M10 bolts are A Good Thing...

Originally Posted by quattrorunner

I was trying to show that he can use different combos in order to come up with what he needed. I have no idea what was used in 67 or even any other years earlier than my 76 my car.
The 100mm m8 bolts flanges fit na cars and the fine spline stubs from a 915 fit a 930 gearbox. His request is for a 915 though. My post is to have him look at his flanges and see what they are. Then he can start the search.

Nah, yeh, good suggestion. Looking in PET, the "Nadella" axles for 68 and earlier look like G50 "attached stub" axles; there is no separate stub axle...

I think I'd be inclined to see what the wheel hub looks like (different part #'s - but who knows what the differences really are - not me); if it'll accept a G50 spline, then would be good with only removing the pins/tapping the early 915 output flanges he already has and buying a set of G50 axles. Or stub axles from a 69-73 car would match the transmission flanges and let OP just bolt in 69-73 axles.

65-68 share the part # 904.331.065.01 for the wheel hub ; 69-73 use 901.331.065.09, 74-89 use 911.331.065.33.

These may simply be catalog rationalizations, or, with the revision numbers, could be completely incompatible changes.

OP may have to swap the wheel hub to suit later axles, perhaps even modify or change the banana arms if it doesn't Just Work, depending on what the differences are.

It may come down to fixing the/finding another 901 being easier. Especially being a '68 - most of the value is in the originality of those, for collectors.

Originally Posted by quattrorunner

But spuggys post comes with lots of info and good threads that could go a long way to answer many questions without getting dirty. Nice

Heh, thanks. I have an extensive bookmark collection from when i had a 915 and I'd check my CV bolts more often than I'd check the oil...

[quattrorunner]

Early on I did shear some bolts. This was before I had a turbo so I believe some had backed out having not been properly torqued? This was a rather dramatic experience for me. Driving at around 90mph and having m8 bolts let go of a spinning half shaft. Imagine that. It was “dramatic”.
After that I drilled some bolts and wired them in series to hep keep them in place better.
Actually that wasn’t even my 76 I drove now but a 79 that was sold.

[Matt Monson]

Too lazy to cut and paste a quote, but fine spline for 915 didn't start until 1978. All 1974-1977 915 use coarse spline stubs.

915 and 930 108mm stub axles are the same part. However 1975-77 Turbo Carrera 930 stubs are unique to those years and a different diff that was fit to them. But any 1978-1988 930 stub will work in a fine spline 915 diff. As was mentioned, 915 didn't go up to 108mm until the mid 80s.

Also, G50 stubs can be shortened to be the right length for 915.

[Seppo]

Friend has some later partsm I will try to use the later 75.5-85.5 CV ,
It should bolt on the early axle