Bill Gregory

Just got back from Watkins Glen, where a club members C4 sheared it's rear hub, just inside of the outside edge of the rear wheel bearing.

This seems to be a failure point, as I can think of two other C2's that sheared their hubs at the same place. With the hub in place, you can't inspect it without removing the hub from the rear wheel bearing, which also destroys the bearing.

When I replaced my rear bearings, I had one hub that had a small crack starting, and the other was questionable, so I replaced both of them. Here's a picture of the hub with a crack started, which is also just where the hub on the C4 sheared this weekend:



Just a caution for those that track their C2/C4's. If you replace your rear wheel bearings, be sure and carefully inspect your rear hubs. New ones are available from Porsche, around $375 each.

MarkD

Yikes.

Do you suspect this is developed in hard driving/track cars only?

Bill Gregory

I've only seen/heard of a handful of failures, and only on cars that are tracked. Hard street driving doesn't approach the stresses that cars are placed under on the track, so unless there's data to the contrary, I wouldn't be concerned with this on non-tracked 964's.

That said, if your rear wheel bearings are replaced, it presents an opportunity to inspect the rear wheel hubs.

bgiere

The left side of the rear hub on my 964 cup was oblong shaped when we went to replace the bearings at the beginning of the season...I imagine it would have started to crack sooner rather than later...The car had about 13,000 kilometers (all racing) at that time.

tafkai

are they not different on an rs ?

Bill Gregory

RS and C2/4 use the same 964.331.065.06. There are two entries in the parts catalog for C2/4 to 91 and 92-on C2/4 and RS, however, only one part number.

Cup car, however, uses a different part, 964.331.065.70.

Turbo and Turbo look also has a different part number, 928.331.065.07.

garrett376

Hey Bill, your picture is zoomed in really close - do you have an image further back to show where that location is - I can't tell where it's at. Thanks

Bill Gregory

I don't have a full hub picture handy......You know the hub that the rear rotor attaches to - the rough part of the metal in the picture is the backmost portion of the hub, immediately next to the trailing arm. The shiny part is what is inserted into the rear wheel bearing in the trailing arm. I'll see if I can snap a picture of the entire hub tomorrow.

garrett376

is it a rotating part, or a fixed part?

garrett376

Ah ha - you mean part number 7, right?

Bill Gregory

Next page in the catalog, part number 7 - it has the lug bolts in it, and turns as the axle turns, rotating on the rear wheel bearing (#2 in lower diagram) located in the trailing arm (#1 in lower diagram).

And what the diagram with part 7 doesn't show is the portion that inserts into the rear wheel bearing.

garrett376

Bill, do you know of the guy was using spacers, or maintained the original offset? I would think that could be a possible etiology...

Bill Gregory

I don't believe he uses spacers on the rear wheels.