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Wobbly disc

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Hi all,

 

After replacing front wheel bearings I noticed one of the discs seems to have a wobble. The discs (textar) were replaced a few years ago and have plenty of life left in them. I'm thinking it could be disc variable thickness rather than a warped disc after doing a bit of googling.

 

Just wondered if anyone else has had this problem and if they tried having the discs skimmed? It's around 70 quid to get done. 

 

Thanks

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1 minute ago, Too late said:

Discs dont cost much these days .   Waste of time skimming etc 

 

I wish, £107 Each for my brembo discs, im waiting for a decent discount code

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I guess the question is how many miles are discs meant to last for? My discs have covered under 10k. The cost of skimming is equal to one disc and it seems more wasteful to replace rather than repair.

 

 

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If the disks were true on the old wheel bearings I'd suspect a seating problem on the new bearings' flanges. Keep in mind that a spec of rust or dust even a faction of a 1/1000" between the disk and hub is magnified greatly out at the pad friction surface. A few years ago I installed new disks & the first one I tried had more than 0.010" runout. I blamed the disk & let me tell you that I was really annoyed, to put it politely. However, at the end of the day I found a tiny, almost invisible, spec of something on the disk's mating surface. Once I cleaned it off the disk was true to better than 0.0005". You need to wire brush and clean the "old" disk seating surface very carefully. And ensure the bearing hub is clean too.

 

Also, do you have the disk firmly clamped to the hub? The set screw alone can't ensure a flat, tight fit on the hub. You need at least 3 of the lugs clamping the disk to hub. Given length and the "missing" wheel you will have to use washers or a clinch nut on the lug bolts to apply clamping force to the disk while checking for runout (i.e. wobble). Otherwise the lug bolts will screw in so far that they will bind on the bearing and prevent rotation to check for runout.

 

BTW, BMW doesn't publish specs for disk "trueness." But 0.002" runout and 0.0005" thickness variation seem to work.

 

Regards,

RDL

 

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Agree with @rdl disc to hub mating surfaces. Needs to be really clean. Clue is after you put the old disc back on new hub. They are a bit of a faff to line up on the hub spigot with the single little securing screw. Take disc off and clean and refit.

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Debris between disc and hub gets my vote too. Sometimes even aggressive wire brushing can leave the tiniest speck stuck to the mating surface. I've even used a scraper on occasions.

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On 15/03/2017 at 10:02 PM, duncan-uk said:

I'd look at the callipers for sticking.

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Duncan is correct. My brakes were under a year old, but a sticking caliper ruined them. Get the brakes hot and then spin the wheel to see if it rubs. If it does, it's likely your caliper. I just put Brembo on all round last weekend.

 

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