SC axle flange threads - common problem & what fix is best?
 

Removed the rightside axle from the differential axle flange on my '78 SC and saw the heart stopping curl of pulled threading (rightside only - all other look great). Two of the six (adjacent) have lost ~ 60% of their viable threading and the rest had to be chased with my 8X1 to even take the 8X1 50mm hex head bolts.

So the question: How hard is it to R&R the axle flange? Is this a part that I can readily find, maybe via our classifieds? Looks straightfoward - lock the diff and remove the center bolt. If you've done this or had this experience I'd like to hear about it.

This exercise was precautionary - I think I dodged a bullet on this by deciding to rebuild the newer half shafts I found and install them this weekend. Looks to me like this particular fitting was getting ready to go loose.

The pulled threads are probably from over-torquing the CV joint bolts at some point..

Bentley and others, incorrectly listed the torque spec about double the 33 ft-lbs that is correct for M8 bolts (6 mm hex).

You can remove the axle flange by removing the stretch bolt in the center of the flange.

I suspect these 100 mm transmission axle flanges are readily available from salvage. Be sure to inspect used parts carefully. Make sure the seal surface is not rusty.

I suspect that a proper Helicoil install will make the threads better than new.

Be sure to replace all the M8 CV joint bolts and the Schnorr washers.

Best of all is to convert to the 108 mm CV joint axles, transmission axle flanges and stub axles. These larger CV joints use M10 bolts (8 mm hex). They were used ’69-’75 and ’85-on. The ’76-’85 911s used these small 923 (912E) CV joints that are barely adequate IMHO. There is an 'art' to selecting the correct set of pieces for this update/backdate.

Best,
Grady

Thank you Grady.

In the process of sourcing an axle flange and installing it. I have two questions:

1) Can I/Should I/Will I have to replace the seal as well? Any advice on doing a seal R&R in situ?

2) I believe I am looking for a "fine spline" axle flange ('78 SC) - can anyone confirm without my transmission number in hand (is stock for that year if that helps).

3) What is the difference between the coarse and fine spline axle flange? What years were they employed?

Thanks to all for putting up with my endless questions...

John

What about re-drilling and tapping six new holes between the old ones?

Maybe weld up the old holes too?

I would helicoil the flange myself if I trusted my ability to keep all threading true - without a drill press I am not so sure I can. That's why I am looking for a flange in good nick. The price to have the local machine shop handle this is comparative to what I am being asked to pay.

Still could use info. on new seal Yes or No on this job. Will for certain use a fresh stretch bolt, M8, Schnorr washers, and liberal use of QTips and acetone to ensure proper torque and peace of mind. I am SO very glad I caught this before the axle pulled from the flange.

This 'Board is the best on the 'net, no question!

John,

Yes, replace the lip seal.

It is not difficult to do ‘in situ’.
You are already there.

Note the position of the old seal in the casting and on the axle flange. You want the new seal at least that far out but no farther. A tiny bit ‘in’ is best so the lip has perfect metal (no rust) to seal on. A ‘pipe tool’ works as a seal press. The Factory tool presses it in where the outside face of the seal is flush with the outside of the casting.

You do not need to replace the single stretch bolt in the center of the flange unless it is damaged.
Absolutely YES replace the M8 CV joint bolts and Schnorr washers.

Any machine shop should be able to install Helicoils properly ‘while-you-wait’ for a reasonable cost. Healicoil threads are stronger than the original.

If you look at the backside of the flange, I think the threaded holes are in a reinforced ‘bump’ in the steel casting. There is not enough material to re-position the holes between the original.

Course (18) splines are prior to ’84-’85.
Fine (43) splines start with the change back to the 108 mm CV joints in about '84-'85.


Please read this thread:
http://forums.pelicanparts.com/porsche-911-technical-forum/222537-reconstructing-constant-velocity-cv-joints.html
While very long, it is the best word on CV joint attachment.
It is worth studying in detail.

Best,
Grady

Burgundy Ben

If you take a look at one of these flanges, you will see that the way they are cast (or forged?) does not lend itself to putting holes other than where they are.

Helicoiling is economical and pretty simple. Anything else short of getting good used ones is not.

Walt

Ok, got it, thanks.

Went ahead and helicoiled the flange. Worked out very well - wanted to close out this thread (so to speak) with that data.

Thanks to all for the information.