Theory & Practice: Rear Wheel Bearing, Races & Hubs

goldgunner · 06-28-2006, 05:36 PM

Once again, I'm might confused...
All ready to press in the rear wheel hub into the bearing and I'm missing some logic and maybe more than that:

I had the local shop press in the bearings into the Trailing Arm.
The bearing does have the 2 inner / inside races, with the split in the middle. Each race is about 22mm wide including the outside radiused edges. The overall width of the bearing is about 44-45mm; the difference being the free floating split in the middle between the 2 races. Here's the pic:

I also had the machine shop press on the outer race onto the wheel hub. The total width of the race is 20mm; the apparent 'effective' width of the race - starting from the edge of the radius closest to the wheel studs is 15mm. The remaining effective length of the wheel hub diameter, not including the end chamfer, is about 18mm. Here's the pic:

The axel shaft which fits inside the hub, mating splines, apparently does not have a race: or at least, I didn't get one with the bearing set.
Is this correct? No race on the inside?
Here's the pic:

Now, here's where I'm baffled:

It will be quite a tight fit to press the wheel hub into the bearings, but with the right tool it seems that a fit is likely.

FIRST HOWEVER: considering the wheel hub only has 15mm to mate with the first (outer) bearing inner race, No mating will occur with the second (inner) bearing inner race. And, the axel shaft doesn't touch the bearing, so - only the outer of the 2 inner bearing races are functional? How can that be? I must be missing something...that's a honking big bearing to only be using half of it.

SECOND HOWEVER: the outer race attached to the wheel hub doesn't, to me, appear to be going to touch or ride anything! From what I can tell from PET and Bentley and other threads I'm not missing an 'outer seal' that this race would lip against. In fact, the edge of it is what will hit against the first (outer) bearing inner race. What purpose does this race serve?

I have to think I must be missing something, or several somethings...

Please - some hand holding, nose leading, detailed elucidation or caustic jeering with info that will fill in my blanks...

thanks as always,
Jim

rcwaldo · 06-28-2006, 05:58 PM

From your images, it looks as though both the inner and outer, inner races are still in the bearing itself, so one would think the inner race that is pressed onto the outer hub is not needed.

goldgunner · 06-28-2006, 06:04 PM

Thanks Chris - That's Very helpful and makes sense.
I have to wonder why I had that extra race in the bearing set...hmmm, or did I? That was performed so long ago I have no recollection of the circumstances.

But, removing that race would answer both of my 'howevers'.

Sometimes, and often for me, the forest does conceal the trees. Thanks for the clear cutting - much appreciated.

Regards,
Jim

Jim Sims · 06-28-2006, 06:08 PM

Where did the race on the hub come from; it looks like a race from a front wheel bearing?! Did the shop understand what they were doing? I think the race on the hub has to come off (which is always "fun") and be discarded. Don't forget to reinstall the backing plate and reinforcing cover before pulling the hub and stub shaft together using the stub shaft nut (no pounding or the new bearing will be ruined).

84toy · 06-28-2006, 06:46 PM

When you knock out a hub, the one race always stays on the hub. If you look at the pics, the color of the race on the hub is clearly an old one. Remove it and all will be good and spacing will be correct

goldgunner · 06-28-2006, 07:03 PM

The fronts all seemed to go together very well: not short any races, bearings, etc. All fit quite well.

I can only speculate that my aged memory is faulty and somehow I left that race on the hub...doesn't make any sense cause I'm almost always anal about the tear out. So, I still have doubts...but evidence is evidence.

I'll dremel cut that race out and press in with the monster bearing remover - presser.

THanks all!
Jim

Steve Marshall · 06-28-2006, 07:16 PM

If you heat the race on the spindle you can knock it right off. It's easier than the dremel and you won't risk hurting it.

Jim Sims · 06-28-2006, 07:23 PM

"If you heat the race on the spindle"

How do you propose heating the race without also heating the spindle (hub)? They're in intimate contact due to the press fit and have essentially the same coefficient of thermal expansion; so how will heating help?

Steve Marshall · 06-28-2006, 07:41 PM

By applying the heat to the race and not the hub (spindle) the race will expand faster. Even though the hub will also expand, the differential in expansion is great enough to free the race and allow it to slip off.

Jim Sims · 07:56 PM

"the differential in expansion is great enough to free the race and allow it to slip off"

Have you actually had this work (and how was the race selectively heated?) with a interference, press fit (not just a "tight" slip fit) of steel on steel? I've never seen it successfully done, as the heat transfer from part to part very quickly "catches up" and nulls out the very small thermal expansion difference.

Steve Marshall · 06-28-2006, 08:07 PM

I have done this several times using an oxy acetylene torch. It has worked great every time. I just apply the torch to the race. The race practically falls off the hub.

Jim Sims · 06-28-2006, 08:23 PM

"oxy acetylene torch"

Then I assume this is only for parts that are being discarded as the heat treatment could be compromised and part geometry distorted at those temperatures and local heating rates.

Steve Marshall · 06-29-2006, 07:24 PM

Yes, the race would then be discarded because the new bearing comes with new races. I've never reused the old races for this reason. It doesn't take much heat for this procedure so I doubt the part is compromised if you need to reuse it. Certainly it causes less damage then grinding on it with a dremel.

84toy · 06-29-2006, 07:36 PM

FWIW and since we are on the topic....Never reuse any componant of a bearing after you put a torch on it. Never mix the races on a double row bearing like the rears. When tightened, the outer and inner race come together in the middle and the clearance is pre-set at the factory with the two races touching. A different race in a bearing of that nature has a serious potential of failing.

Steve Marshall · 06-29-2006, 07:41 PM

84toy - Great tag line.

goldgunner · 06-30-2006, 01:10 AM

Thanks all for the input.

Since I have no oxy acetylene torch to remove the race, my option was limited to the dremel. And yes, even with a cautious approach a 1/6" blade width by about .02" deep groove depth occured longitudinally. Not preferred, but not at all a meaningful structural concern.

Thereafter, using the Porsche bearing remover - installer tool to draw in the hub, things went easily.

Yes Jim - thanks - I remembered to install the backing and reinforcing plates first. Having now completed assembly of the e-brake components on one side, it appears that it would have been easier to perform that also prior to hub insertion. Oh well, live and learn.