S2 Hubs

[944Fripp]

Hi all. Been a while, I hope everyone is staying safe and well.

My S2 passed its MOT today with no advisories! Yay!

However, I also asked them to check the runout on the front disks because I've been getting some brake judder and they're way out..but not warped. Turns out both font hubs are distorted and themselves have a runout of 2mm (I know the garage well, they're not pulling a fast one and based on my knowledge of 11 years of ownership and use it makes sense!) hence the judder.

So, what can I do about this? New hubs are £660 each from Design 911 which is really not an option! Alternatively I could get a couple of 2nd hand ones and hope they're good. I've never heard of hubs distorting before so the chances are 2nd hand ones will be OK.

Finally could the existing ones be machined back to flat? But then I loose some metal.

Does anyone have any advice? What would you do?

Thanks for your collective wisdom as ever!

 

[bmnelsc]

Too many variables here to say what is the right "fix"...
Is this runout checked with the bearings in or out? The bearings centralize the hub so the condition of the bearings makes a difference...and if you want to eliminate the bearings you still need to have the outer races in place as these are where the bearings ride to centralize the hub. Or if no races the hub must be mounted so that the axis of rotation is the bearing race surfaces. Perhaps you could mount the hub via the flange and measure the bearing race surfaces for runout.
Old or new bearings for runout measurement?
Bearings properly adjusted? slack in the adjustment would create slack in hub. When adjusting the bearings if you don't tighten them up quite snug and then back off to get the washer to move as described in the workshop manual...you may have left too much slack (being taken up by extra grease) in the bearing then when as soon as you run it this extra grease is squeezed out to the appropriate film and you have loose bearings.
So - all these things make a difference in determining if the hub has runout and if there is runout it should be coming from wear on the spindle axis e.g. where the races are pressed into the hub.
So to measure this properly I would install new bearings and races - oiled rather than greased - adjust to factory spec and then measure runout. You would of course disassemble and properly grease pack the bearings before running this on the road.
So - how do you fix this?
Well if the axis of rotation is true to the center of the hub and it is indeed the flange that is whacky I would think you could turn them true again...2mm isn't a lot to loose in thickness of the flange. But which side? I would guess you would want to do this on the side the wheel mounts so the wheel is running true without runout.
If the axis of rotation is whacky (due to bad bearings wearing the surfaces that the bearing outer races fit on) then you need new hubs or machine out the hub surfaces and install a bush to that it will take a new bearing race perfectly centered.
All of the above assumes the spindle is within spec and not abnormally worn or even slightly bent. Bad bearings can wear the spindle where the bearing inner races mount and this could show up as runout on the hub flange as well. If the spindles are worn then its time for new ones or have the bearing surfaces built up with weld and machined back to spec.

So as you can see - new or gently used hubs may not solve your problem at all. You need to definitely identify the source of the runout before you can make a correction that will solve the problem.

 

[Paul 290T]

Tom 2mm is massive. Even at brake disc edge the run out spec is maximum 0.1mm. If you had 2mm at the hub this would be something like 4mm at the edge of the brake disc. Would the wheel even turn?

I am not doubting you have hub distortion, its just not 2mm. Get the hubs to a machine shop. They will centre them on a lathe and turn them slowly and measure the run out accurately. Then you will know what the situation really is.

If the hub is distorted then the bore where the bearing goes will also be distorted, not just the disc mounting flange, though perhaps to a lesser extent. You need to know the extent of bore distortion as this will change the bearing fit, and therefore bearing life. Designers choose different "fits" for bearings to allow for various operational parameters that ultimately affect bearing life span. If the bore is oval then machining will yield a circular bore, but the diameter will increase and the bearing won't fit correctly any more.

Personally I'd buy a pair of used hubs, get them measured as described above for piece of mind and move on.

Paul

 

[944Fripp]

Thanks Paul and Bruce, those are both fantastic answers.

I'll admit, i didn't follow the correct installation procedure and didn't know to back off the tightening so I suspect this has contributed, if not caused the problem. It makes sense as I did both bearings and the car does spend a bit of time stationary so I can see how the grease may build up and cause this, I did think 2mm was excessive and that it was odd that they were both the same. I've got the manual now and can see where I went wrong so thanks for pointing this out.

This has been going on for some time now so I'm going belt and braces. I've found a good looking 2nd hand set on ebay and have ordered them. They come complete with steering knuckles/spindles too which may or may not come in handy (always good to have some spares kicking about). I'll get them cleaned up and checked at a machine shop before fitting with some new bearings which I'll fit using the correct procedure this time!

If I still get the same problem I know it's not the hubs and I can then get the spare spindles checked.

I'm interested to learn more about oil rather than grease. What do you use and how do you get it into the bearing as well as prevent it from flowing out? How much do you use? Given that the car does spend a fair bit of time stationary I think this could be better for my car than grease.

Fingers crossed and thanks again to both of you.

 

[944Turbo]

I think the oil was a temporary measure while you take runout measurements - the problem with grease is you might have a thicker bit initially in one area- that is why there is the suggestion to tighten and then back off - it should 'level up' the grease around the bearing,
Tony

 

[Waylander]

you cant run oil in the wheel bearings,

you will loose it all, have a bearing seize and the wheel fall off,

If oil was the correct thing to use then there would not be grease instructions in the manual, I have replaced 100's of wheel bearings over the years, only rears on fixed axles have oil in them, and thats gear oil.

you need to check the run out on the hub face rather than the disk, check that first, if the hub is flat then the disk is not sitting flat on the face of the hub, 2mm run out is huge, the manual states maximum of .05mm lateral on the hub and 0.1 on a fitted disk!

 

[944Turbo]

hence Bruce putting
"So to measure this properly I would install new bearings and races - oiled rather than greased - adjust to factory spec and then measure runout. You would of course disassemble and properly grease pack the bearings before running this on the road."
Maybe he should have put before lowering wheel to ground!

 

[944Fripp]

I think the oil was a temporary measure while you take runout measurements - the problem with grease is you might have a thicker bit initially in one area- that is why there is the suggestion to tighten and then back off - it should 'level up' the grease around the bearing,
Tony

Yup, that makes a lot more sense! []

Thanks again all.