Four bolt flanges ? What is up with that ?

[Gytis Kupinas]

I , recently, purchased 108mm coarse flanges to accommodate turbo axles with early 915 trans. Axles fits but there are only four (4) threaded bolt entrances .

Why ?

Anyone can explain ?

[M_deJong]

4 bolts and two roll pins. That's how both my 71 and 74 are... I think SC's went to 6 smaller bolts.

[Jon B]

There are no coarse-spline 108mm flanges with six bolt bores.

There were two basic coarse-spline 108mm flanges, 901/911 and early 915, and both had four 10mm bolt bores. The 930 Turbo Carrera was first 108mm flange with 6 bolts (10mm), but fine-spline (photo below), while non-Turbos downsized CV's to 100mm with six bolts (8mm).

What is the part number on your flanges, and what is their overall length?



Jon B.
Vista, CA

[M_deJong]

Jon, thanks for the education. Were the 6 bolt 100mm flanges coarse spline? I ask because I'm pretty sure I have some coarse spline 6 bolters in my spare 915 but not sure what size they are and its easier to ask you than to go dig them out and look!

[Jon B]

Mike,

Yes, those flanges had 923 part numbers- coarse spline, 100mm, six 8mm bolt bores.

Jon B.

[Jon B]

There were two basic coarse-spline 108mm flanges, 901/911 and early 915...

I should add there were some variations, flanges for ZF differentials and possibly 108mm flanges for '69 901's with aluminum cases, but all were coarse-spline and four bolt.

Jon B.
Vista, CA

[Gytis Kupinas]

thank you .
great info.

should i leave as is and try my luck only with four bolts? or should i drill it and thread it with time sert ?

[Jon B]

Gytis,

I have no idea what model car you're working on, what you're building, its intended use, or if the parts you have will work properly together. The fact that you've hit a problem here suggests it hasn't all been researched thoroughly.

You might see if the 10mm spiral pins used with those flanges fit tightly in your CV's. I wouldn't run four bolts alone without the spiral pins. Maybe someone has run Helicoils or TimeSerts in the unthreaded bores with success, but I have no experience with that to recommend it.

Jon B.

[Hellraiser]

I'm running the four bolts alone without problems.
only noticed it when I removed the engine last month.

[Gytis Kupinas]

Jon B., there was no research at all, you right about it. I needed to make my 86 turbo run again ( turbo motor problem ) , so I had 3.2SS sitting (just built ), and there was this 76 915 in a corner mated to 2.4S........
Long story short, electric gizmos ,of turbo, bypassed. 3.2SS with Webbers in 86 turbo chassis running and.....turbo axles won't mate to flanges on 915........

that is when research started how to.......now all is working except I'm not in my comfort zone with only four bolts holding axles to flange.