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Hi All. Newbe here. I have appreciated earlier posts describing the slow speed brake pulsing I also get on my just bought 2010 R1200GS, with 19k miles. Previous posts indicate BMW did admit the problem and issued two bulletines and referenced a revised rotor - but this only helped under warranty. So, I'm trying to do run out measurements on my front rotors to find the pulsing cause. Question: How does one apply a dial indicator to a rotor that has a whole lot of holes drilled in it? I have set my dial follower on the outside 1/4 inch of the machined rotor face cuz that's the only place there isn't any holes. Is that the preferred method? I'm finding a.004" to .005" variation this way but wondering if this is a legitimate technique. Thanks gentlemen. Your help will be appreciated.
 

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You are doing the right thing, max run out will be on the outer edge. Ideally the run out should be less than 0.002".
If your DTI repeats well you could always lift the plunger and rotate the disc 90 deg, taking a reading at each position.
You should also measure the disc thickness for variation, less than 0.001" is required. This is often the main cause of brake pulsing.
 

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You are doing the right thing, max run out will be on the outer edge. Ideally the run out should be less than 0.002".
If your DTI repeats well you could always lift the plunger and rotate the disc 90 deg, taking a reading at each position.
You should also measure the disc thickness for variation, less than 0.001" is required. This is often the main cause of brake pulsing.
Very much appreciated, Molly. I have slowly rotated the rotor 360 degrees five times on the dial indicator and get very closely repeated readings in the same places each time. The .004" to .005" variance is about 180 degrees across from the .000" reading. (BTW, I also miked the rotor thickness a while back. Got about .002" variation there.) Can I impose on you once more? The left rotor runs out with at, or less than, .001". Can I just replace the right rotor? I assume the right rotor cannot be "turned" to reface it due to the cooling holes in it, right? Thanks again.
 

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That 2 thou thickness variation could be significant. If the other disc is within spec I see no reason why only one rotor is replaced. When fitting a new disc it is important you clock the run out after bolting up.
Don't even think about skimming the disc far better to get a new one. It might even be cheaper to buy two after market discs instead of one OEM.
To avoid future problems change the pads to EBC HH items.
 

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Discussion Starter #5
That 2 thou thickness variation could be significant. If the other disc is within spec I see no reason why only one rotor is replaced. When fitting a new disc it is important you clock the run out after bolting up.
Don't even think about skimming the disc far better to get a new one. It might even be cheaper to buy two after market discs instead of one OEM.
To avoid future problems change the pads to EBC HH items.
[/QUOTE]
Another gem. Thanks for the help Molly. Will do. Helps make up for the dealer mechanic who charged for my brake check and said, "They're fine."
 

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You can't really cut them but they can be centerless ground. I seem to recall that for my XS I had the rotors drilled and then ground for under $100 each but I sure can't find the contact info for the guy that did it....
 

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You can't really cut them but they can be centerless ground. I seem to recall that for my XS I had the rotors drilled and then ground for under $100 each but I sure can't find the contact info for the guy that did it....
"TRUEDISK.NET"...owner's name is Tom Tokarz. Runs his shop in Michigan.
 
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