Advice - Aluminum Trailing Arm with pre-74 Hubs

[katigbr]

I recently completed installing a set of Aluminum Trailing arms with the original hubs and stub shaft from my 72T. I learned in a recent post (cstreit) that there is a 5mm difference in bearing surfaces between the pre-74 steel and 74- aluminum arms.

The stub shaft now sits around 5mm lower in the now protruding pre-74 hub and the old cotter pin holes are unuseable.

My concerns are:

1) Can I use the pre-74 hub with the alu arms without running into bearing problems? I'm assuming that I've got the same amount of bearing surface as a pre-74 car but am losing the advantages of the wider bearing. Am I asking for trouble?

2) Cotter pin holes. If I can safely use the pre-74 hubs, can I drill new cotter holes in the stub shafts without compomising the strength of the shaft?

3) I'm assuming that the 5mm difference is similar to adding a 5mm spacer to the hub and will give me a wider track, which could cause some rubbing with 245/50 tires.

4) The parking brake seems to engage okay, but am assuming that the pads are now offset 5mm from where they should be. It looks like I have enough space but are there any worries here?

Thanks,
Rick

[jluetjen]

I think that I ran into the same problem when I updated my '69 with aluminum arms from a '76. In my case the stub axles were interfering with the bearing carrier on the trailing arms. I just ended up buying a pair of used stub-axles from a '76 to match the arms. They were pretty cheap. I got them from Foreign Intregue in Maine who happens to be local. I think that you might be able to also get the same things from Pelican or your local used Porsche Parts source.

[Early_S_Man]

Hey, GIBSON! Did you have the disappearing cotter pin hole when you did your conversion, or not??? Or, is the answer NOT to MIX the early stub axle with the LATE HUB? I've got alu arms, and both kinds of hubs waiting out in the garage on this job. If early hub and stub axle fit the later bearing of the alu arm OK ... that would seem to be the ideal solution!

[Britwrench]

One thing should be born in mind with this hub-swapping;
If you are going to use 17" or bigger wheels you MUST be able to use the hub to center the wheels. When Porsche went to the 17" wheel the tightening technique was changed because it was felt the the wheel nuts alone would not correctly center and hold the wheel tight to the hub (in other words, the wheel nuts could come loose). All 17" and larger wheels must be torqued with the weight off the wheel.

[GIBSON]

Warren, I did the swap just last month. I used a pair of 76 aluminum trailing arms in my 73 coupe. I removed the hubs from the 76 and used the existing hub from my 73. They slid into place and torqued fine, I used a new cotter pin but probably could have used the old one. The CV joints slide into place with no problems, I've just had one test drive around the block so far but things seem fine. The axle length is right, I can't see any reason to change any other parts. The bearings must have a larger O.D. but the same I.D.

Bruce