Grinding noise from rear when cornering

[zcacogp]

Chaps,

My S2 has developed a grinding noise from the back. It's on the left hand side of the car, and only occurs when going 'round a right-hand bend (i.e. when the left hand side is loaded up). It's related to road speed and is a constant noise - as opposed to a clunking or ticking noise. The tyres and wheels are standard (D90's) and the suspension isn't lowered.

I've had the rear wheels and brakes off and can't see anything that looks polished or rubbed. Has anyone else had experience of this sort of thing and, if so, what caused it?

I'm suspicious of the handbrake shoes as they are badly worn (pretty much worn out) but driving along with the handbrake on doesn't cause the noise to happen. Another possible culprit would be a rear wheel bearing (although the one on that side was changed about 60,000 miles ago and the noise isn't the constant droning which I associate with a wheel bearing).

Any suggestions from the more knowledgeable chaps on here will be welcomed - thanks.


Oli.

 

[chrisg]

Oli

as you've aluded to, the noise from the rear is when rear left wheel is loaded up. As you've done the wheel bearing I can only conclude it must be:

1. Outer CV joint
2. Inner CV joint
3. (long shot) diff bearing on one side - although unlikely as would be probably be the same on both sides...

4. Something rubbing/ catching on the wheel such as bodywork ?

Yours

Chris

 

[zcacogp]

Chris,

Thanks - I was hoping you would comment. I'm slightly inclined to doubt it's the CV's as it's not a CV-ish noise and they were all replaced about 50,00 miles ago. Same applies to wheel bearing; they drone at all speeds when duff, rather than making a rubbing noise when loaded up.

The noise occurred at the same time as I was playing with the brakes (trying to trace a shimmy in the brake pedal which turned out to be a warped rear disk) so I am wondering whether I have disturbed something in either the handbrake or the calliper. Does this sound at all plausible?


Oli.

 

[edh]

Is there anything catching in the brake backplate?

Something quite small can result in a sizeable noise through the car.


...or is the car leaning over so far that the side mouldings are scraping on the floor? []

 

[chrisg]

Ed good suggestions. ISTR that Oli ha removed the thin steel backing plates from his car both front and back.

Oli it's likely that if uve had the brakes apart inc the handbrake mech it's something lose or misaligned with those. Daft questions I know but did u tighten up:

1. Rear caliper ( inc with the spacers between the caliper an the hub)
2. The two small cross thread screws that locate the disc
3. Outside chance,( but done it myself....) the 5 wheel nuts ?

Chris

 

[zcacogp]

Chaps,

Thanks for the helpful suggestions. I've had it all apart and had a good look and I think I know what it was. It seems that, for some reason, the disk is sitting slightly further inboard than it should be and was just catching on the bolt head for one of the bolts that holds the bracket underneath the hub assembly. (The bracket is a lightweight thing and is only to support the cotton-reel type wiring connection). There was definite wear on the bolt head and if you looked closely at the disk you could see dragging marks on it. Treating the symptoms was easy (grind the bolt head a bit flatter) but this raises two further questions;

1. There is a bit of deflection in the assembly when cornering as it doesn't rub all the time. Is the wheel bearing shot and should it be replaced? I happen to think not; there is no play detectable in the bearing when you wobble the wheel MOT-style. There will always be a tiny amount of deflection no matter how good the bearing is when you are asking it to bear the cornering forces of a tonne of car at 40mph.

2. Why is the disk sitting a mm or so further inboard? It's not a function of the disk as it rubbed with the old disk as well (this disk has only been on there about 400 miles.)

And this is the interesting question ... why would a disk sit slightly inboard of where it should be? All suggestions on a postcard to the usual address .... thanks.


Oli.

 

[edh]

Wrong bolt length possibly?

 

[zcacogp]

Ed,

Nice idea but no; the bolt in question probably hadn't moved since it was inserted in the factory, 24 years ago.

I'm wondering whether there is any feature of the hub design that allows the brake disk to move in slightly. I don't know enough about the way it is all bolted together to understand what's what, but do know that the grinding started when I removed the old disks and cleaned the mounting faces on the back of them up to try and eliminate the run-out on them. I subsequently swapped the disks and the grinding got a lot worse (pretty much continuous) but has died back since then.

(I'll add the caveat that I am not 100% this has cured the problem; that which I saw has fitted all the symptoms but I have yet to test-drive it after the 'repair'. It may yet prove to be something else.)


Oli.

 

[bmnelsc]

I wonder if the bearing you got for replacement was slightly narrower than the original (allowing the hub some lateral movement as the bearing moves back against the control arm inside bearing face and then out against the circlip) or perhaps the control arm is worn on the inside face where the bearing sits against it? Or maybe your circlips are wearing and new ones are needed?

Otherwise, its hard to imagine what would allow the disc to move in to an interference position when cornering one direction and later move out of the interference position (possibly when cornering the other direction)? Your description of the noise getting worse after cleaning the mounting surface of the discs (moves them a little closer yet) and also when swapping the discs (you got a new unworn surface on the noisy side which subsided after a while because the interference spot wore in on the swapped disc).

 

[zcacogp]

ORIGINAL: bmnelsc

I wonder if the bearing you got for replacement was slightly narrower than the original (allowing the hub some lateral movement as the bearing moves back against the control arm inside bearing face and then out against the circlip) or perhaps the control arm is worn on the inside face where the bearing sits against it? Or maybe your circlips are wearing and new ones are needed?

Otherwise, its hard to imagine what would allow the disc to move in to an interference position when cornering one direction and later move out of the interference position (possibly when cornering the other direction)? Your description of the noise getting worse after cleaning the mounting surface of the discs (moves them a little closer yet) and also when swapping the discs (you got a new unworn surface on the noisy side which subsided after a while because the interference spot wore in on the swapped disc).

Bruce,

This is the sort of knowledge and thinking which I need - thank you. I am not that well acquainted with the way the bearing holds the axle laterally in place, so your words there are particularly helpful. My challenge to your logic is that the bearing was replaced soon after I bought the car (60,000 miles ago) so if it was a smidge narrower than it should be (maybe on the extreme end of the width tolerance range) then the problem would have come to light earlier. I'm hoping that the control arm isn't worn, but I guess it may not be any great shakes if it is. A new circlip is an interesting idea.

Your logic about the progression of the noise is identical to mine.

I guess my question now is whether I need to do anything more about it. Should I be thinking about changing the bearing/control arm/something else, or is it fine as it is? If there is no noticeable play in the bearing (and I hadn't considered lateral play, thanks) and everything is holding together as it should then should I be concerned?


Oli.

 

[bmnelsc]

Oli, Thank you for the kind words. After looking at the PET again, one more option for wear that might allow lateral movement is the stub axle itself - particularly the shoulder that fits up against the wheel bearing inner race. I'm not sure but it appears that the hub could be tightened up to correct torque but effectively bottom out on the splines rather than getting down to the proper clearance on the bearing inner race so the stub axle might have some lateral play rather than the bearing itself.

As to your question about leaving well enough alone...its probably OK for the time being but I think the longer you leave it - the more parts you will need to change to sort it all out. It seems to me that you keep on top of your Porsche and even if its not a safety issue now, I don't think you will allow it to continue too long because you know something is wrong back there.