924Board.org

[emoore924]

Over the years, I've had some play in the rear wheel bearings for my 79 924 n/a. Nothing major, just something I keep an eye on each time I tech the car.

The 36mm castellated nut that holds the assembly together gets tourqued to something like 300ft-lb and is cotter pinned, so it ain't falling off anytime soon.

Yesterday, I replaced the wheel bearings hoping the play would be reduced or go away entirely -- no luck, no change.

Any ideas on reducing the amount of play? It is not excessive but I'd like to understand why it is there and what might be done to fix it. Short of removing and replacing the swing arms, what about machining the spacer, using shims, etc.

Thoughts?

[emoore924]

Anyone? Anyone? Beuller? Beuller?

[gohim]

When you replaced the wheel bearings, did you replace the spacers, and thrust washers as well?

The thrust washers and spacers wear and crush down over time. If you didn't replace them, you would still have play when replacing the wheel bearings.

And the wheel bearings themselves, where did they come from. Remember, bearings are sold in different grades with different tolerances. If you bought cheap bearings, manufacturing tolerances could explain the play that you noticed.

[Smoothie]

This's been discussed before, so you might have some luck with a search.
As I recall, the most likely correct answer was to replace a pipe-shaped spacer that's in there between the bearings.
_________________
"..it's made in Germany. You know the Germans always make good stuff."


'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

[John Brown]

Hi Ed.

Again.

I am of the opinion that they were never 'tight'.

The torque on the axle nut has nothing to do with the play that you feel. Sketch out the bearing layout and really look at what is holding things together and it will become obvious.

Still trying to figure out why the internal spacer crushing a little bit would have any appreciable effect on the play. Not that I can see.

I also have put brand new bearings all around (name brand), checked for out of round. Bought and used the proper thickness internal C clip behind the ball bearing. And, all the play is really in the fit of the outer roller bearing. Which ain't adjustable.
_________________
John
80 931 - #931 44Cup
99 Escalade - tows track cars
gone but not forgotten: original 924.org car - 82

[Joes924Racer]

I had a failed bearing and replaced inner and outer bearings got them from napa where did you get your bearings from these are for my 79
runnin 83 944 hubs.
_________________
1979 porsche 924 Na
1980 porsche Turbo 931GT Replica
Have u ever driven a turbo.

[emoore924]

Thanks folks.

The spacers/washers were not replaced.

The bearings are SKF I believe. Not cheap.

I will search...

John, I will sketch out...

I guess this might be one of those "factory installed" features that you can't do anything about... But, I feel better if this is the way it is...

[gla924sem]

Went through the same thing with my 924. Sent may Emails back and forth to Tom Charlesworth the 924 Tech guy from PCA.

His final comment: Watch the wear and if does not get worse it was meant to be. How much $$$$ do you want to spend going after a ghost

[John Brown]

Ed et al:

I have written this up before; here goes:

If you look at the stub axle you'll see than everything, and I mean everything, just slides onto it and the axle nut squeezes it all together trying to make the complete assembly act like it was solid. So, while this is not the way you have to assemble it, conceptually you can envision the axle with both bearings and the spacers all assembled and snugged down.

Then you can invision sliding the complete assembly into the arm. Now, the only part that actually holds the axle into the arm is the retaining clip that holds the ball bearing outer race (inner). So, any LATERALl play that exists when you pull and push on the axle is a result of the space between the shoulder than butts the ball bearing ourter race and the inside of the retaining clip, and the clearance between the balls and the races. There are different thickness retaining clips in the parts supply. THE AXLE NUT HAS NOTHING TO DO WITH THIS PLAY!! Also, this is not the 'rocking' radial play we almost always are checking by moving the wheel.

Since the ball bearing is holding the axle assembly at the inner end it won't do much at all about radial play of the axle at the outer end. Assume the outer end of the axle was not support by a bearing. Even imperceptable play at the inner end would be magnified by the time it got to the outer end (or, the wheel edges). So, while not to be ignored, it turns out the inner bearing has a limited part in 'rear bearing play'. Note for the record that the inner bearing outer race in my experience is a press fit into the arm. But not a real severe press. A light tapl.

That leaves the outer roller bearing. Go back to envisioning the axle with all the bearings stacked up and you can see that the outer bearing is free to move laterally in and out. It is a simple roller bearing and the rollers are not constrained in lateral motion (except at the extreme of course). So, unlike a tapered bearing, no amount of torque on the axle nut will have the slightest effect on the play in the outer bearing either laterally or radially.

Finally. The radial play in the outer roller bearing is what controls what we thing of as wheel bearing play. In my experience nothing about this bearing is impressive in fit. Neither the bearings themselves (inner and outer races and rollers) nor the fit of the races on the axle and inside the arm. Nothing is even press fit. The outter race is an easy hand fit, The inner race slides onto the axle. And the rollers have some play in the races. Again: THE AXLE NUT DOES NOT CONTROL THIS CLEARANCE.

I have not done hundreds of these cars. But I have done half a dozen. It SEEMS to me that the 924s are loose. The 931s a little tighter. The 944s same as or slightly better as the 931. None of them without some play. Quality control?

More than one axle has been ruined (stretched or stripped) by someone 'fixing' the play by snuggin up on the axle nut with a big impact wrench. I have even seen professional techs pronounce the play "improved" after such an excercise. Remarkable what expectations do to human objectivity.
_________________
John
80 931 - #931 44Cup
99 Escalade - tows track cars
gone but not forgotten: original 924.org car - 82

[emoore924]

Wow John, thanks for taking the time to write that up. That's 4 sure the best explanation I've had and I certainly trust the source. I'll think it through but on first blush the argument holds water and I'm on board. I've had this concern (I won't call it a problem because like you I'm not convinced there is a problem...) pretty much since I bought the car in 92 but there has been little change with over 10,000 racing miles. So, I think it is safe to say that what play exists is a result of exactly the situation you describe above -- factory installed (for the 356, it was oil leaks, for the 924, clunky rear wheel bearings...)

Thanks again

[John Brown]

Ed;

Two areas of wear are possible to exacerbate this situation; but I don't think they are root causes.

1) Bear races spinning and galling and wearing the axle or the hub,

2) pounding the hub egg shaped.

I have seen no signs that either is a significant factor on the cars we have had here.

I got into this early on because of going through the very very good tech Potomac Region does for DE cars. Some of the folks, amatuer and pro, understood. Some of them did not. Those that did not tend to be inexperienced and all caught up in the 'Porsche specifies no play' mantra. So, I sat down with the parts in hand and made myself a picture. There are really two issues: How much play and does the axle nut affect it.

The later alloy arms use two big ball bearings and are much tighter.
_________________
John
80 931 - #931 44Cup
99 Escalade - tows track cars
gone but not forgotten: original 924.org car - 82

[Joes924Racer]

the bearings spinning in there race 'ahh that sounds nasty' and 'yea that was some spiel. I have even seen professional techs pronounce the play "improved" after such an excercise. Remarkable what expectations do to human objectivity.

My 79 had a side tighter than the other I mean when it was all together
the axle was way easier than the other. Works good. 'Oh' and pack the amount of grease they way to in there along with the bearings.
_________________
1979 porsche 924 Na
1980 porsche Turbo 931GT Replica
Have u ever driven a turbo.