930 CVs onto 901 Stub Axles

Jim2 · Jim2's Garage

Couple questions guys, maybe someone has done similar. I'm mating 930 CVs onto 4 bolt/2 pin style stub axles. If I were to machine up pins to fit in the 930 CV and stub, would the 4 bolt arrangement be sufficient? It's not a drag car, street going 930 drivetrain sub 400hp.

The alternate is to weld up the two pin holes on the stubs and tap them so I have 6 volt CVs, but wondering if welding heat would interfere with whatever heat treating was done to the stubs. Am I overthinking this?

Matt Monson · 05-31-2021, 03:52 PM

What gearbox? A 930 gearbox has fine splines and those stubs you want to use are coarse spline. They won’t work in that gearbox without a new diff, which requires fresh ring and pinion set up. That alone will cost you more than just buying a set of 930 stubs.

Jim2 · Jim2's Garage

That's a stub from the wheel flange end of the axle which I'm looking at driving with 4 bolt/2 pin or welding the two pin holes and tapping in order that it accommodates 6 bolts. I'm suspecting lots of people have welded these and tapped them without any issue but it would be nice to hear.

Long ago when I harvested this turbo drivetrain which was in a SC chassis I took the axles but left the stubs behind in the trailing arms.

Matt Monson · 05-31-2021, 05:04 PM

Your picture of the gearbox and stub threw me. A 69 901 gearbox stub is 4 bolt, 2 pins and 108mm, like a 930 gearbox flange.

jpnovak · 06-10-2021, 12:49 PM

Yes, easy. Drill the 930 trans to 2pin, 4 bolt. The axles should already have the 2 pins in place.

4 bolt 2 pin will be fine. Likely that the shear strength of the roll pin is higher than the bolt due to diameter and lack of threads.

Only thing I am not sure of is axle length - or transmission output flange to output flange dimension. 901 would be 10 3/16".

Jim2 · Jim2's Garage

"Jamie, the one stop source for all Porsche info"

Thanks once again Jamie. I was thinking along the same lines that there must be decent shear strength in those roll pins, negates the weld and taping where hardening may be an issue.

As I mentioned I do have the axles which I harvested from the donor turbo swap SC, 930 CVs on both ends. Based on your advice I'll install 901 roll pins into my outer 930 CVs to mate to my 901 stubs. Inner end of my axles will bolt up with all six bolts in usual fashion.

Couple more days and I'll be ready to rock n roll, sort of.

stownsen914 · 06-20-2021, 03:01 AM

I'll offer a counterpoint. My 911 vintage racer came to me with a similar setup. It seemed to work fine strength-wise, but the inner CVs puked all their grease every single track weekend. What a mess. Long story short, the 4 bolt 2 pin stubs were flexing and dumping the grease at the pins (I discovered this when I resorted to wrapping the CVs with duct tape to contain the grease splattering *everywhere*, and noticed pockets of grease forming at the pins). I had the pin holes tapped and timeserted to accepted 10mm bolts, to make a 6 bolt flange. Easier than welding, and I prefer to avoid welding heat treated parts when possible. Solved the problem for me.

Jim2 · Jim2's Garage

Sorry stownsen, my notifications no longer seem to work, not sure why.

Thanks for your feedback, good to hear of an identical installation. I dropped by my machine tool guy asking for a cobalt tap and described my idea of welding and tapping but he was concerned that the weld would harden and even cobalt wouldn't "cut it". He then suggested a threaded insert! I gave this some thought but defaulted to Jamie's advice that shear pins would be at least as strong as the bolts. Seeing you have success with threaded inserts will be my backup plan. I'm going to keep an eye on the 4-bolt arrangement to ensure they remain tight and will resort to the inserts if needed.

Since there is no gasket allowance in this arrangement (early 930 cv to 901 stub) I did a trial with a tiny trace of sealer around the inner perimeter of the cv, bolted up the stub and torqued the bolts. When I separated them the sealer only spread about 1/4" wide on the inboard circumference and left the remaining mating faces metal to metal. Fussy to apply the sealer with an art brush but *looks* like it will do the job, though as you say if the four bolt flange is flexing and grease comes out then I go threaded inserts.

Installed my axles yesterday but not before discovering the cv bolts collide with the aluminum trailing arm when using 901 stubs. A little fancy machining action ensued and all is good now.

stownsen914 · 03:48 AM

My application may well be more demanding since it's track only. 4 bolts / 2 pins might be fine for a street application. The challenge I had was getting sealant to work. It would puke grease at the perimeter near the pins no matter what I did. I also have no gasket. With the 6 bolts, I've been able to use Curil T (non setting sealant) to seal. So far, so good.