Author Topic: Front Rotor Warped - Can you get them machined?  (Read 5676 times)

Offline 2000rsv

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Front Rotor Warped - Can you get them machined?
« on: August 31, 2012, 10:27:29 AM »
'86 K75C with 21k miles (non-ABS).  The front rotor imparts a slight pulsation when applying the brakes.  Feels like when the front rotor on my truck gets warped.

Put a new front skin on and had the dealer check the runout of the rotor while doing the balance.  Runout was about 0.004".  Still stops fine (for an anemic K75 front brake) but the pulsation bothers me.

OK, the question.  Is there anywhere that turns/machines the front rotors so they're flat?  Or do I need to replace it?

Thanks,  J
AMA 1097757, IBA 33089, TS 700
2000 Yamaha RSV, 2008 KLR650, '86 BMW K75C, and always a couple of projects

Offline frankenduck

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Re: Front Rotor Warped - Can you get them machined?
« Reply #1 on: August 31, 2012, 10:58:43 AM »
I took some to a machine shop once and they said there wouldn't be enough meat left after they turned them.  I've never heard of anyone having them turned.  YMMV.
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Offline harper

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Re: Front Rotor Warped - Can you get them machined?
« Reply #2 on: September 01, 2012, 11:22:39 PM »
They don't turn them, they have to be ground. Stainless is too hard. I'd live with the pulsations as long as the rotor has the thickness in spec. 

Rick G

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Re: Front Rotor Warped - Can you get them machined?
« Reply #3 on: September 02, 2012, 12:24:52 AM »
I have access to a disc grinder and tried to do a front disc but because of it being thin in the first place it wouldnt come out true.
You have to put a small pressure on the disc face for the grinder to work but even with that pressure they warp and wont grind true.
I have ground a lot of discs from the Jap bikes on that machine and they always come out true but not the K series BMW. Many of the earlier discs were OK.

Motorandy123

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Re: Front Rotor Warped - Can you get them machined?
« Reply #4 on: September 02, 2012, 07:35:10 AM »
Generally a "warped" disk is not warped. There is material from the pad embedded in the surface.
You can try Scotchbrite and water or wet sanding to clean it up. Or bed in the new pads by harsh
braking until everything is hot. That will put a new later of material on the surface.

Offline 2000rsv

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Re: Front Rotor Warped - Can you get them machined?
« Reply #5 on: September 04, 2012, 11:41:01 AM »
Generally a "warped" disk is not warped. There is material from the pad embedded in the surface.
You can try Scotchbrite and water or wet sanding to clean it up. Or bed in the new pads by harsh
braking until everything is hot. That will put a new later of material on the surface.

I had the disk runout measured while being balanced after a tire change.  Warped may not be the right term, it may be uneven wear (or uneven buildup) rather than warpage.  Will likely just live with it since there appears to be plenty of meat on the rotor.

However, I will test out the Scotchbrite idea the next time I put pads on.

Thanks all for the information and experience.

J
AMA 1097757, IBA 33089, TS 700
2000 Yamaha RSV, 2008 KLR650, '86 BMW K75C, and always a couple of projects

Offline Honolulu

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Re: Front Rotor Warped - Can you get them machined?
« Reply #6 on: September 04, 2012, 10:12:27 PM »
+1 on several hard stops from 70+ mph.  Bimmers and beemers probably both appreciate a good scrubbing now and then to kill pad squeal and possibly brake shudder as well.  There was a time, years ago, when the 5 series had MAJOR brake shudder issues.  Mostly it could be ameliorated with some hard stops.  Non-sporty drivers were having a hellofa time, as were the dealers.

Offline chrish8846

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Re: Front Rotor Warped - Can you get them machined?
« Reply #7 on: September 07, 2012, 08:43:09 PM »
Had the same problem as you earlier in the year, cured it by lightly sanding both sides of the discs with a air die grinder. I had a rust buildup on the rotors as the bike had been sitting a while.
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