Why different CV joint sizes?

[caproader]

Guys,

When I took my 912 apart, I noticed that the 912 CV joints are thicker than the CV joints on my 73 S. The 912 CV joints use 55 mm allen attaching bolts while the thinner CV joints on the 911 use 48 mm allen bolts. The 69 parts book mentions that the 48 mm bolts are used in a 'light' CV joint.

So what's the deal? Why are there two sizes of CV joint? It seems strange that a 912 would require a stonger CV joint than a 911. Are the joints interchangable on the drive shaft or are the drive shafts different size? Now that I have a 73 2.7 MFI, it seems logical to put the larger CV joints on the stronger car and put the 'light' CV joints on the 912. Unless there is a reason to do otherwise.

Enquiring people want to know. Thanks for the thoughts.

John, proud member # 322
73 S with sportomatic, 2.7 MFI (originally a 73 T), and 912 in pieces

[Alan.uk]

Its because the 915 gear box is wider.

Incase anyone is interested, here is a pic of the two different sized CV bolts.



Alan

[Zithlord]

Hi Alan

Where did you get those parts cad plated, or is it yellow zink (new parts?)

Best
John

[Alan.uk]

Hi John,

It's all zinc plated, most it is yellow zinc chromate and some clear. I get it all done locally to me. I get quite alot of stuff done these days. Here is few bits for my friends SWB car.





Alan

[Alan.uk]

Combine new parts with freshly plated and powder coated parts the results look much better

Before



After





Alan

[caproader]

Alan,

Thanks for the information. Which obviously means that the different size CV joints are not interchangeable. But what about the driveshafts? I had a collection of driveshafts from the 912 and a couple 73 911's in the garage. When I re-built the complete 1/2 shafts for the 912 (with the thicker CV's), I did not compare the lengths of the drive shaft. Is it possible that I used the wrong length drive shaft when I re-built the complete unit?

John in Asker: I use a guy in Dayton, Ohio, USA for my cad plating. Everytime I go up there, I am afraid that the EPA has shut him down. But so far he is still there.

John

[Alan.uk]

Hi John,

To be honest I am not 100% sure. I can take a look tomorrow when I go back out to the garage.

Thanks

Alan

[caproader]

Thanks Alan. I'll check in here tomorrow.

John

[Alan.uk]

Hi John,

I am going to get some pictures, as at first glance they look the same, but I would like to take a closer look.

Alan

[caproader]

Alan,

I measured the two I had left over from a 911/915 I parted out and they were both the same length. So if I screwed up, I screwed up twice, with 2 drive shafts. Or they are all the same length. I'm hoping for the latter.

John