How do you test for a warped rotor? - BMW Luxury Touring Community
 
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post #1 of 10 Old Jan 19th, 2008, 1:45 pm Thread Starter
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How do you test for a warped rotor?

I am pretty sure one of the frount rotors (disks in UK) is warped. Don't know which one though.
Is there a good way of testing?

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post #2 of 10 Old Jan 19th, 2008, 1:55 pm
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You can use either a dial indicator and check for runout (the best way) or you can sometimes take off the calipers (so wheel turns freely and with the front tire off the ground, just spin the front wheel and looking from the front you will see the wobble.

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post #3 of 10 Old Jan 19th, 2008, 2:03 pm
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Cool

I was told to put a zip tie on the front fork and pull the tie end around to the rotor. Just close to it. Then turn the tire to see if the tie end moves away from the rotor. Cut it off when finished.
Cheap tool!

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post #4 of 10 Old Jan 19th, 2008, 3:29 pm
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Quote:
Originally Posted by bblalock
I was told to put a zip tie on the front fork and pull the tie end around to the rotor. Just close to it. Then turn the tire to see if the tie end moves away from the rotor. Cut it off when finished.
Cheap tool!

Now that's a good idea! See, I mechanic'd in the days before cable ties!

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post #5 of 10 Old Jan 19th, 2008, 4:11 pm Thread Starter
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Well I just gave the cable tie idea a go, makes sence to me to do it this way but nothing seems wrong.
My symptoms when riding were like I was breaking harder and softer when I was pulling the break leaver steady. It just felt a little jerky.
Anything else cause this?

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post #6 of 10 Old Jan 19th, 2008, 5:27 pm
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there is a rotor on ebay if you can pick it up, always stick it back on there if you dont see a difference in results
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post #7 of 10 Old Jan 19th, 2008, 5:40 pm
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Could have been the pulsation of the ABS if it did it when you were braking hard. I would certainly clean the disc with some Brake Cleaner...wipe it down good and try it again under controlled circumstances. BTW, are your brakes integrated??? Could be the rear rotor if they are.

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post #8 of 10 Old Jan 19th, 2008, 6:28 pm Thread Starter
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No idea if '99s were integrated actually.

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post #9 of 10 Old Jan 19th, 2008, 7:11 pm
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I didn't notice that it was a '99 They were not integrated until 2002 I believe. I would clean the rotors very good - wipe them down with a clean rag saturated with brake parts cleaner and give it another go. Hope you get it corrected.

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post #10 of 10 Old Jan 20th, 2008, 10:34 am
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Quote:
Originally Posted by c00k1e
I am pretty sure one of the frount rotors (disks in UK) is warped. Don't know which one though.
Is there a good way of testing?
There is absolutely, categorically no way a rotor can warp.

This is an old wive's tale that has been passed down from generation to generation by shade tree mechanics. It lives on to this very day.

What you are feeling is uneven deposition of brake pad material on the surface of the rotor, usually caused by improper bedding in or light braking forces. The typical scenario is that the rotor is checked for thickness variation (run out) - and low and behold - the disc is "warped."

You can attempt to clean it off with garnet paper and a palm sander, but the material that is deposited is extremely hard and abrasive. If you catch it early enough this will work, before the deposition has gotten thick. It is worth a try. Don't use regular sand paper since the aluminum oxides in it will leave a residue behind and make the problem worse.

You can also purchase some abrasive brake bads, install them for a while and attempt to clean them in this fashion. Unfortunately I don't think they exist for the LT.

The only other thing you can do is Blanchard grind them to get a new surface - but I think the LT's discs are made from steel, not iron - so this is probably not a possibilty unless you can find a specialist shop that would tackle this. Even if you go this route unless they are properly bedded in during initial use you'll probably end up with the same problem again.

Unfortunately the only way to cure this is with new pads and new rotors.

Kaching! $$$


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