smiffypr

re: the 928 front wheel bearings are set up with clearance, not preloaded or set up with zero clearance like many others manufactures recommend.

One reason is that the ally hub expands with heat (mainly from the brakes), and the stub axle being steel expands much less.
So that the bearings are not preloaded when hot, they need some clearance when cold.

Smiffy

blown 87

The hub could expand all it wants, the bearing and race is still steel, just like all the other Timken bearings.

smiffypr

When the hub expands, it makes the outer races of the two bearings further apart, same effect as pulling the inner races closer together, just as if the adjuster is tightened.

Smiffy

blown 87

Uh, maybe.

Lizard928

just a note, the front wheel bearing washer has a tongue on it to prevent it from rotating. So using the spinning of the washer method will not work on the 928.

I set the 928 front wheel bearings with just a slight (maybe half a thous) preload. I find that a lot of 928s tend to get a slight shake at 130kmph and this prevents this.

I have track days, and many many miles on the cars I have done this too and have never had an issue.

One thing that is different with the 928 over most cars is that the hub of the 928 that the bearings sit in is aluminum and does expand with heat. Where as the stub shaft is metal and does not. I suspect that as things heat up the tolerances become slightly less.

smiffypr

Re: A high speed bearing is a bearing designed and toleranced for high speed. Even when it is not turning, it is still a high speed bearing.

I looked up the spec for one of the bearings which I fitted, it is rated for up to 17,000 rpm. That would make it a high speed bearing to me.

I have a picture of my bearing that failed due to using moly grease, but I can't see how to include it here.

Smiffy

WallyP

I decided to do some more research on the subject of "no moly in roller bearings".

Turns out that like almost everything nowadays, there is no agreement. I found a few lubrication companies that had moly greases that were recommended for bearings, and some that said not to do it. I found a lot of anecdotes one way or another.

At the moment, my conclusions:
- A lubricant that is too good can cause a lightly loaded high speed bearing to fail if the rollers skid rather than rolling. I won't use moly grease, Teflon grease, silicone grease, etc., in my power tools.
- A lubricant can't be too good in a heavily loaded, low speed bearing.
- There are some really good "wheel bearing" greases out there now. The biggest change over the last few decades appears to be heat resistance.

My opinion is still that a soft moly grease will work fine in a wheel bearing, because it is a heavily loaded low speed bearing.
My opinion is that there are better greases out there for wheel bearings, especially if you get the brakes really hot.
My opinion is that wheel bearings are designed to work with as close to zero preload and zero clearance as you can get, and the "finger method" is the most reliable way of getting that.
My opinion is that the "move the washer" with little force from a screwdriver is Porsche's way of getting zero preload and zero clearance.
My opinion is that most wheel bearing failures are due to dirt and maladjustment during maintenance.

YMMV

depami

That being said, and not knowing the history of a 24 year old car, should I go into them?

They “feel and sound” good. Can I simply remove the cap and check the grease? Or will that show nothing?

davek9

How many miles on your Shark?
IMO if it is more than 100k, then cleaning / inspecting and re-packing w/ mobil-1 syn can't hurt IF you follow Wally's instructions.

Tighten the clamp/nut with wheel turning, stop the wheel, then back off clamp/nut until you can just move the washer side to side w/o prying (it won't rotate for reason stated above).

DaveK9

mark kibort

Ive tried a bunch of grease. the good old hi-temp grease from your local automotive store will work best. again, emperical testing on a 928 race /street car with more track hours than any other one out there. they synthetic grease just ran out of the bearings and out of the seal cup at racing temps. you have to understand, at racing temps, the wheel bearings and wheels get over 250 degrees. Im always amazed how the heat doesnt melt the tires!

dr bob

This is the stuff I use regularly, and it's available at most local parts places:

http://www.mobil.com/USA-English/Lub...tic_Grease.asp

The Redline CV-1 product is very similar. The Mobil-1 high temp limit is stated to be 305ºF, and perhaps MK's experience with hot brakes and hubs suggests that this isn't a good candidate for his racing conditions. For the rest of us, it's more than adequate.

Lizard928

I would love to see someone move/spin the washer on a 928 front wheel bearing!
They are keyed so as to not move.
This works on many other cars, but not the 928

dr bob

The washer is hardly a snug fit on the spindle threads, and has easily enough 'wiggle room' to use as a guide to correct tension. At least on my car. I have an experience base of one 928 on this subject, and the WSM method worked fine on that one sample. I bow to those who have more/different experiences with multiple cars, however.

Lizard928

most I have done have not had very much wiggle room at all, and that washer has been a relatively snug fit.
In conjunction with that being able to move the washer with a screwdriver is again not an accurate method as everyone will apply a different surface pressure, and should anyone have a mark on the screwdriver that can dig into the surface they will get more grip and therefor will run their bearings tighter.

mark kibort

Yep, I had no issues with it, until I hit the track. Then, it became a huge mess! Nothing like the old lithium based, high temp wheel bearing grease!