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BMW 3-Series (E90 E92) Forum > BMW E90/E92/E93 3-series General Forums > Regional Forums > UK > UK Technical Forum > Brake Wobble.



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      10-09-2012, 01:46 PM   #23
Flood
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I have a 2006 E92 2.5 auto. I bought it 6 months ago and it developed a wobble after a couple of thousand miles. I took it back to non BMW dealer I bought car from and they replaced only front discs(not pads).

After another 6k miles it started to wobble again on braking. I took it to a local BMW specialist workshop and he refitted new discs and pads. The hubs were pretty rusty and he cleaned them all up. One of the wheels had been dip coated as a refurb and the inner wheel had this plastic on. He said that the discs use the wheel as additional cooling. He said that the wheel would not have been straight on the hub due to coating and that the heat may not have dispersed correctly may have led to disc warping.

160 quid for OEM discs, pads and sensors fitted seemed OK to me compared with dealer, so I will see how I get on.
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      10-10-2012, 12:34 AM   #24
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Brake discs don't warp per-se, they suffer from DTV - Disc Thickness Variation - which causes judder to be felt.

Often caused by sloppy fitment by young garage employees. Discs should be fitted and checked for runout before fully reassembled.

I've seen garages coat the hub flange area with copperslip grease - that is a big no no!! That area needs to be spotlessly clean.

I have an on-car lathe to true up any discs that aren't running perfectly true. Skimming the discs off the car (which happens in 99% of cases) is no good.
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      10-15-2012, 07:46 AM   #25
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Interesting, I have had something similar with my fronts - it is on about 66k miles but they are the originals, so the discs should not have ever been off for anything to get between them and the hubs.

It is a funny one because it is very noticeable from about 65mph upwards but absolutely nothing below that. In warmer weather and if I give the brakes a real pasting - such as a track pad break in procedure - it seems a bit better. And when the rear discs and pads were changed this summer, it went completely, only to return after a few thousand miles. That was really odd.

It is an auto, but I try not to sit on the brakes after any remotely hard braking. I keep meaning to get the front pads/discs changed to see if it sorts it, but BMW's costs are high and the fact it is only at high speeds makes me vacillate - especially when plenty of people on here have done this and not seen a benefit! It seems a common BMW thing - maybe it is made worse by the soft bushes designed for RFT...
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      10-16-2012, 02:12 PM   #26
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Quote:
Originally Posted by Subzero2003 View Post
First of all, discs very very rarely warp, and almost never do through road use. When people diagnose "warped discs" what they almost always mean is "friction material from the pad has transferred to the disc, meaning that the disc is very slightly not flat". Automatics are particularly susceptible to this as if you come off a motorway onto a slip road - you may have just braked fairly hard from 90mph down to 0mph. This heats the pad massively and then when you are sitting at the traffic lights with your brakes applied, this transfers the pad material slightly to the disc.

Just to confirm, when the various garages have changed the discs, the problem has gone away completely for a few months?
Correct and the most likely cause. The garages that have replaced the older discs have don't it for 2 reasons, to line their own pockets or they have no understanding of pad transfers effect on the wobble under braking.

Fix - Brake from 80 to 30 hard 3 times and then drive without using the brakes for a bit - a motorway at night and then you will be fine, unless the discs have a lot of pad transfer build up.
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      10-23-2012, 03:11 PM   #27
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Braking from motorway speeds to a standstill wouldn't put in anywhere near enough temperature to cause pad transfer, you're talking about needing 600C plus before that kind of thing happens.

All discs have a level of DTV and judder as new, this will deteriorate over time through temperature cycling or in some cases pad transfer. This is normal though and should only be noticeable to the driver in extreme cases.

The reason a driver can feel it is usually because a small amount of run-out or DTV has built up and old or worn out bushes are no longer capable of isolating the vibration from the driver. Replacing the bushes will fix it unless the run-out/DTV is really bad, changing the discs will fix it temporarily, until that small amount of runout/DTV has built up again. The usual culprit is the FLCA rear bush, (or the equivalent depending on suspension architecture).

'Re-bedding' the brakes as BMMiniparts mentioned will temporarily reduce the DTV, but it will eventually come back.
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      10-24-2012, 03:10 PM   #28
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Quote:
Originally Posted by bigandy View Post
Braking from motorway speeds to a standstill wouldn't put in anywhere near enough temperature to cause pad transfer, you're talking about needing 600C plus before that kind of thing happens.

All discs have a level of DTV and judder as new, this will deteriorate over time through temperature cycling or in some cases pad transfer. This is normal though and should only be noticeable to the driver in extreme cases.

The reason a driver can feel it is usually because a small amount of run-out or DTV has built up and old or worn out bushes are no longer capable of isolating the vibration from the driver. Replacing the bushes will fix it unless the run-out/DTV is really bad, changing the discs will fix it temporarily, until that small amount of runout/DTV has built up again. The usual culprit is the FLCA rear bush, (or the equivalent depending on suspension architecture).

'Re-bedding' the brakes as BMMiniparts mentioned will temporarily reduce the DTV, but it will eventually come back.
Strange this. I have had my car for 5 months, done 10k miles and never had a brake wobble issue.

It is all about understanding why brake wobble evolves. Automatics are more prone because of the nature of sitting on the brakes when at traffic lights, junctions etc.

Never brake heavily to a standstill and sit on the brakes, let the car roll half a turn and use the handbrake.

Avoid long braking stops, where the pads are incontact with the disc.

Every now and again brake hard to deglaze the discs to remove the pad transfer.

Alternatively lift of the accelerator sooner so the car weight slows it down - thus saving fuel. Then brake but with more power thus not sitting on the brakes for too long.

In addition you should never need to brake when on any dual carriageway or motorway, except for roundabouts or slips roads thus reducing the pads transfer risk. I know of people who have got 80k miles from a set of discs.

It is all down to driving styles, not the actual parts, just how they are used.
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      12-16-2012, 09:55 AM   #29
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Bit of an update with my problem - taken a while because I learn't to drive round my wobble as it only did it under light braking- that and finding the time to fix a non serious issue is difficult!

Anyway- penciled in a money throwing exercise - starting with two new back tyres and a referb of the wheels. Suspected one buckled front- found one front and one rear - so got them all refurbed job lot. Anyway I fitted the wheels myself- lazily used a rattle gun... still had the brake wobble and seemed to have a slight wheel balancing problem so got them checked at the wheel refurb place- they were slightly out so got then sorted- then fitted the wheels, albeit properly with a torque wrench.

On the drive home the car was perfect- really smooth/vibration free and weirdly my brake wobble has gone... Which is good because I was about to change the hubs/ discs / control arms- I'm still suspicious it may return though but goes to show how sensitive these car are. I think i'll change the control arms anyway and do a wheel alignment for piece of mind and to keep the tyre wear even.
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      12-16-2012, 06:16 PM   #30
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I had a thread on this somewhere...

You MUST measure the hub flange runout especially on older/used cars.
I was surprised how much mine had, so I replaced both front hubs.
Braking issue resolved permanently.

I had the on-car brake-lathe work, two disc sets from different manufacturers, always trouble shorlty after.

And the EBC discs were really crap - runout from the box exceeded BMWs oem specs, poor QC.

The big brakes on the 335 are especially problematic due to the large diameter - they need to be spot on.
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      12-17-2012, 07:14 AM   #31
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Update on mine as well - I had the front discs/pads replaced last week (the rears were done 5k miles ago). They had plenty of wear left on them but I thought that after 70k miles I could not complain about replacing them! I now have no vibration at all under braking - we shall see if it returns...

In my case I know this was never the wheels as I have summer and winter sets, and also an "all square" setup and rotate fronts to rears to even the wear - it was always the same on all sets.
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