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Discussion Starter · #1 ·
My 2000K1200LT has ABS, but the front brakes pulse a lot when used. The rotors were checked and deemed OK by a mechanic using a dial gauge. The tires up front were badly cupped so I changed out both tires. The same mechanic took off the pads and examined them. They appeared good for wear and even thickness. The rear brakes work good and have no pulsing. The front is so bad that the brake lever moves about 1/2 inch back and forth during braking. Any answers or ideas?????
 

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Tire could be out of round. The lever being pushed back though sounds like a problem with the ABS unit unless the rotors have a thick spot on them which I have never seen. I'm not saying it can't happen, I've just never seen anything like that. Try pulling the ABS fuse or relay and then give it a try.
 

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Was the brake fluid ever changed?
 

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Discussion Starter · #4 ·
The tire is not out of round, but the fluid could be the problem or the ABS may be the source. I will try both possibilities.
 

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You've either got a warped rotor or a bent wheel...Only thing that will make the brakes pulse..

It's most likely a warped rotor...... You should be able to put the bike on the center stand. Spin the wheel and figure out which it is right quick...If it's as bad as you describe it shouldn't take a rocket scientist or a dial guage to figure it out.. One of the calipers may actually move around...Just spin the wheel and very gently apply the brakes..Just enough to make them drag. It should be as obvious as the nose on your face...


Sorry you're having problems... Got to be a rotor...The ABS is pretty harsh so I think You'd know it if it was the ABS..After re-reading your post I guess the ABS could be a possibility... Definately disable it temporarily to check ....1/2" of movement in the lever is severe at best...And you'd hear the ABS pump doing it's thing if it was the ABS...Might listen for that...

Good Luck

John

John
 

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When you took the bike and the tech checked the rotors with a dial... Did he do it with the rotors on the bike? Or did he remove the wheel?
If he did not take the wheel off it would be a good idea to check the bolts on both calipers and make sure they are tight.
While you are at it, check the 17mm bolt on the left side of the axle , and the 2 pinch bolts at the bottom of the fork tubes for tightness.
 

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There is no such thing as a warped rotor. This is a shade tree mechanic fairy tale that has been passed down since disc brakes were first introduced and has no factual basis - period.

You have classic uneven pad deposition on the surface of your rotors caused by light braking. The material that has accumulated in "hills and valleys" is called cementite and is a ceramic. It is invisible. Depending on the alloy the rotor is made from there are variations on this ceramic material, but they all are essentially the same. It is extremely hard and can only removed by blanchard grinding or sanding with progressively finer grades of garnet.

Unless you can find someone to turn your stainless rotors - which is highly unlikely - the only cure is new rotors and pads or sanding, which is a lot of work - as in an hour of sanding once the rotor is off the wheel.

Below is a picture of a rotor that was successfully cross hatch sanded with garnet and returned to service. Why garnet? It does not leave behind any residue which becomes embedded in the metal. You get to start over with an impurity free surface which will then allow EVEN transfer of pad material. After sanding proper bedding in of the new pads is essential or you will have the same issue all over again.
 

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Good one Ron
 

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You can actually see the measured uneven pad deposition and "pulse" in the graph below. This is what everyone thinks is a "warped" rotor. It is so minute it can't be measured by a traditional dial indicator until the depositions build up dramatically.

In the thermograph you can see the exact location of the depositions causing hot spots as the rotor turns at high speed. The heating up - as show by the white areas - is caused as the pads momentarily contact the tops of the "hills". The pad floating up and down the hills and valleys causes the pulsing felt in the lever. The thermograph shows a traditional automotive rotor with inboard and outboard discs separated by vanes, but the same sensation is felt in a single solid disc.

When the hills and valleys are removed by either blanchard grinding or aggressive garnet sanding the surface is leveled and the pulsing stops.
 

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Uh oh! :corn:

This is historically where the vast majority of respondents line up against the previous poster who then defends his position nearly to the death.

Let's save a whole bunch of time, energy and angst and just read this post. Anything and everything that could ever be said on both sides have the issue has already been said. And said again and again and again and again.....................

The discussion starts in earnest at post #10.

http://www.bmwlt.com/forums/showthread.php?t=56267&highlight=warped+rotor

FWIW it is very easy to put some 120 grit garnet paper on a random orbital sander and remove any deposits, real or perceived, from the rotor

Nothing to see here. Please move along.

Loren
 

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wa1200lt said:
Uh oh! :corn:

This is historically where the vast majority of respondents line up against the previous poster who then defends his position nearly to the death.

Let's save a whole bunch of time, energy and angst and just read this post. Anything and everything that could ever be said on both sides have the issue has already been said. And said again and again and again and again.....................

The discussion starts in earnest at post #10.

http://www.bmwlt.com/forums/showthread.php?t=56267&highlight=warped+rotor

Nothing to see here. Please move along.

Loren
The problem here is that nobody can or has provided any scientific evidence that rotors warp. They can't supply any because it does not exist! :rolleyes:

It is truly amazing that supposedly intelligent people will defend an old wives tale down to the bone, when confronted with absolute measured, scientific proof beyond any doubt supplied by the Society of Automotive Engineers that they are living in a world of fantasy. This is the definition of denial.

I find it absolutely hysterical that someone can claim they've "seen and measured a warped rotor."

The old wives - or in this case - the old bikers tale lives on... :rotf:
 

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I never knew that Ron. Thanks for the post.

Best from Gorham Maine.

Bob
 

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RonKMiller said:
.....end snip
The old wives - or in this case - the old bikers tale lives on... :rotf:
Yes it does.

It's still not too late to just let it go...............

Loren
 

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RonKMiller said:
The problem here is that nobody can or has provided any scientific evidence that rotors warp. They can't supply any because it does not exist! :rolleyes:

It is truly amazing that supposedly intelligent people will defend an old wives tale down to the bone, when confronted with absolute measured, scientific proof beyond any doubt supplied by the Society of Automotive Engineers that they are living in a world of fantasy. This is the definition of denial.

I find it absolutely hysterical that someone can claim they've "seen and measured a warped rotor."

The old wives - or in this case - the old bikers tale lives on... :rotf:
Are you serious ? I "assisted " my warped ,bent, whatever you want to call it rotor back to acceptable runout, (measured with a dial indicator) with an adjustable wrench. Really. ;) But I do NOT condone or reccomend this procedure........
 

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I'll bite.

Ron, if a rotor cannot warp answer me this. When I take one to the auto parts store and have it "turned" or "cut" and the machine takes a smaller amount off part of the disc than it does off the other doesn't that mean that it's not symmetric? If it's not symmetric then isn't it warped? Have you never seen lateral run-out on a rotor sometimes caused by a bad hub? If I understand your position correctly you are saying that basically the rotor has more drag on one part of the rotor than the other. I do not believe this could physically cause the brake lever to push back out which is obviously due to hydraulic pressure, yes? Now granted, inconsistent drag or coefficient of friction on the rotor would cause pulsing in the vehicle but it would transfer into the tires and you would feel it in the entire vehicle, not the brake lever. While I don't doubt your scientific data, I do doubt it's interpretation. Then again, I've been wrong before.
 

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Let me clarify something. I have seen many rotors with lateral runout on motorcycles and cars. That is what I consider to be a warped rotor. It normally is caused by corrosion (rust) between the hub and the rotor or on motorcycles between the wheel and the rotor. This allows the rotor to seat unevenly on the hub and causes the lateral runout. The primary cause of this is improper torque on the lug nuts when they are left too loose. On a motorcycle it can be caused by a bent wheel or corrosion under the rotor. You can also have a poorly machined wheel which appears straight but has the rotor tabs uneven. In a nutshell the rotors in either situation will conform to the material they are bolted against and a perfectly good rotor will show lateral runout.
 

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Forget it ... deleeted
 
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