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      06-11-2012, 04:58 AM   #1
Sk00v
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Wobbly when braking

Hello

I have a problem with my 2006 e91.

When I'm braking from speed, like when coming off a motorway onto a slip, I get a lot of vibration in the car and the steering wheel. It does do it when when braking at slower speeds as well but is not as noticeable.
If I slow to a crawl and brake I think I can feel it "pinching" periodically like a buckled wheel on a bicycle would do.

I read some posts on here and other forums suggesting pad deposits and warped discs. So I started by doing some brake cleansing by braking hard from high speed a few times as per a tutorial. This didn't fix it.

Since my OBC said my pads would need changing in a few thousand miles, I thought I'd replace all 4 pads and the discs on the front too. After doing this I followed a bedding in tutorial. This has also not helped the problem.

I have also changed the wheels (from winter to summer) which hasn't helped.

There is no wobbling etc whilst driving at any speed so I don't think it's a balance problem.

Any pointers at what to try next, or where I should be looking?

Thanks
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      06-11-2012, 06:46 AM   #2
tmarshall57
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The hub to disc mating surface needs to be absolutely free of any rust or other contamination when replacing the discs. My guess is that the this is the source of the problem.

It could be warped discs if they are of poor quality or have been abused. I think that the only real answer is to check for run-out on each disc and either replace the discs on the axle concerned or, as a first pass, remove each discs and clean the mating surfaces until they are spotless.
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      06-11-2012, 06:50 AM   #3
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Not sure if an e91 has thrust arm bushes - they were notorious on the E39 m5 for giving exactly the same thing. I replaced two sets.
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      06-11-2012, 06:57 AM   #4
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Just looked at the parts diagram - its reversed from the E39 but will have the same effect. They are basically wishbone bushes. No 10 in this diagram
here
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      06-11-2012, 08:05 AM   #5
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Other members here have reported excessive run out in the actual hub bearing assembly which manifested itself as brake wobble (not general running wobble despite the whole wheel being out)

This run out could appear after a curbing or pothole crash.

The replacement hub assemblies are fairly cheap (100/pair for top end SKF parts) from europarts etc and quick to change, with just 4 bolts holding them in.

Part 5 here http://www.realoem.com/bmw/showparts...35&hg=31&fg=10
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Last edited by doughboy; 06-11-2012 at 08:18 AM.
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      06-11-2012, 08:25 AM   #6
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Thanks for the tips everyone. If we get some fair weather in the near future I'll take a look underneath.
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      06-11-2012, 08:35 AM   #7
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You won't know the bushes have gone by looking - need to get under it and try to wobble bits with a bar (a ramp job I suggest).
If i were you i'd book it in for someone to look at.
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      06-11-2012, 02:17 PM   #8
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If your bushes have gone you should also be able to feel the steering wheel 'pulling' over ridges in the road, solid white lines etc.
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      06-11-2012, 02:28 PM   #9
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How far are your discs and pads gone? Mine started doing exactly as you described about a week before I changed them all round and they were pretty much gone. Since the change all has been well.

Apologies but just a small

I'm interested in hearing more about the bushings as I have noticed mine starting to grab at camber changes and undulations but figure my geo may have gone out since changing the wheels. Something I'll be sorting once I get a new suspension setup.

Cheers
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      06-12-2012, 07:08 AM   #10
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Quote:
Originally Posted by bigandy View Post
If your bushes have gone you should also be able to feel the steering wheel 'pulling' over ridges in the road, solid white lines etc.
Now you mention it, I think it may do this a bit. I think I'll get it up on a ramp to take a look.

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Originally Posted by B005T3D-G View Post
How far are your discs and pads gone? Mine started doing exactly as you described about a week before I changed them all round and they were pretty much gone. Since the change all has been well.
A couple of thousand miles, if that. I just changed them. I thought that might be what the cause was originally which is partly why I replaced them.
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      06-12-2012, 02:24 PM   #11
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Quote:
Originally Posted by Sk00v View Post
A couple of thousand miles, if that. I just changed them. I thought that might be what the cause was originally which is partly why I replaced them.
Sounds like a different problem then. Definitely get your hub run out checked along with the bushes and report back as I may need to do my bushes by the sounds of things. Time to upgrade to M3 stuff me thinks
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      02-22-2013, 04:32 PM   #12
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Well, long overdue but thought I'd post the solution.... Changed the front discs again and lower control arms (as one failed the MOT). Still wobbled.

Finally decided to change the rear discs after two mechanics advised "it's DEFINATELY not rear disks"..... It was.
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      06-02-2014, 08:05 AM   #13
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Sorry to dig up my old post, but thought I'd report back.

Quote:
Originally Posted by Sk00v View Post
Well, long overdue but thought I'd post the solution....
Turned out to be a temporary solution as the brake wobble came back..... swapped the discs AGAIN on the rear. Fixed...... came back a few months later. Had the discs machined on the car with a Procut lathe. Fixed. Now a few months on, it's back again!

I bought a dial gauge and it's the O/S rear that has the most runout, but only about 0.08mm compared to 0.02 on the N/S. I checked this before I had them machined.

There was no runout on the hubs that I could detect.

I stripped and wire-brushed the caliper to remove all the rust and greased all the moving parts last time I fitted new discs but could it be this??

The one positive I've had out of this, is from never changing brake parts before, I can now replace discs and pads in about 10 minutes per corner

I'm considering selling the car now as it's doing my nut!
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      06-03-2014, 07:54 AM   #14
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Hi Mate, Just read through your thread, I've got exactly the same thing, had my breaks changed all round twice. Apparently its because the car sits for long periods of time. What Bull****, i didnt spend all that money so that it messes up. I completely agree with the wanting to sell it part. Might don a break upgrade and see how it goes from there....
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      06-03-2014, 08:46 AM   #15
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Out of interest, you arent greasing up the mating surfaces on the back of the discs are you? I know copper slipping the backs of the discs where it mates the hub is known for causing wheel wobble/brake judder issues...
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      06-03-2014, 11:19 AM   #16
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Quote:
Originally Posted by umut335i View Post
I completely agree with the wanting to sell it part.
Yep - extremely annoying isn't it.


Quote:
Originally Posted by Marshall878 View Post
Out of interest, you arent greasing up the mating surfaces on the back of the discs are you? I know copper slipping the backs of the discs where it mates the hub is known for causing wheel wobble/brake judder issues...
As I've done it many times now I've done one set of discs with nothing, then another set with some engine oil on the hub (recommended by a mechanic friend to stop it rusting so quick) and it made no difference to the wobble either way. Thanks for the suggestion though - all very welcome!

Cheers
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      06-03-2014, 11:24 AM   #17
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do yours squeak at all?
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      06-05-2014, 03:44 AM   #18
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Yes the do squeak a little bit, but only when braking. Is that what you meant?
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      06-05-2014, 07:42 AM   #19
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Have you spun the wheels with the car jacked up. Might just pinpoint the problem
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      06-05-2014, 08:35 AM   #20
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Yep, they spin fine. It's only when the brakes are applied that they wobble.

I've even put it on axle stands and had the car 'moving' in 1st to see if i could see anything wrong
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      06-05-2014, 11:44 AM   #21
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I had a similar problem years ago on a new car after its first service. The problem was front wheel judder when braking. Different front pads were fitted and front discs were checked. Did not help. Softer front pads made no difference either. I traced the fault myself to oval rear brake drums caused by overadjusted handbrake at the first service. The excess heat caused by the rubbing shoe had distorted the drums. The shape of the drums then sent hydraulic pulses to the front brakes which were the more efficient disc brakes making everybody believe it was a front brake problem. I wonder if the same thing is happening here, ie a fault on the rear discs is being transmitted to the more efficient front brakes along the hydraulic lines.
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