axle bolt thread engaugement question

[inaminit]

Helping a friend with a 77 911. He was told that he needed to install the half moon plates under the heads of the M8x 50 bolts that clamp the CV joints to the inner and outer flanges. So, with the plates, they only stick out proud about 6 or 7 mm, or 5 or 6 threads where they screw into the flanges. This does not seem enough. The parts book indicates only 48 or 50mm are used. Are we missing something? Thanks in advance!

[ErrorMargin]

Originally Posted by inaminit

So, with the plates, they only stick out proud about 6 or 7 mm, or 5 or 6 threads where they screw into the flanges....

This post by Grady Clay is a good starting point. The thread is long, but it is worthwhile to read the whole thing.

Grady states that you should use both Schnorr washers and moon plates even if your car did not originally come with them from Porsche. After bolting the CV to the transmission with the moon plates and washers and torquing them down to the correct value, you should have 1-2 threads protruding from the back side of the transmission output flanges. If you don't, get longer bolts.

Have your friend get the Schnorr washers and try to torque it down. If there is not enough length on his bolts to see 1-2 threads on the back side of the output flange after torquing (or too much), take some measurements and buy new bolts. Make sure he gets the correct Class 12.9 Allen socket bolts.

[Tim K]

I believe that the later mid-year cars should have the smaller 100mm cv and (x6) M8 bolts (per end).

I also believe that the only cv with the halve-moon plates would be the larger 108mm cv with (x4) M10 bolts (per end).

Yes, use the washers.

Since you mentioned the bolt length, I'll say - it depends. The O.G. boot flange is thicker than the thin aftermarket part. What he has currently may depend on what CV boots are in the car. The O.G. bolts will actually contact the side of the trans while tightening after installing the thinner aftermarket boot kit (ask me how I know). Yes, 1-2 exposed threads is minimum.

The earlier 915-equipped cars (73-74?) would have the M10 4-bolt CVs. Somebody here may have more specific info on this.

Hope that helps.

Tim K