Front brakes pulsing...why????? - BMW Luxury Touring Community
 
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post #1 of 32 Old Aug 17th, 2011, 9:54 pm Thread Starter
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Unhappy Front brakes pulsing...why?????

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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post #2 of 32 Old Aug 17th, 2011, 10:03 pm
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Re: Front brakes pulsing...why?????

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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post #3 of 32 Old Aug 17th, 2011, 11:19 pm
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Re: Front brakes pulsing...why?????

Was the brake fluid ever changed?

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post #4 of 32 Old Aug 18th, 2011, 7:39 am Thread Starter
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Re: Front brakes pulsing...why?????

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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post #5 of 32 Old Aug 18th, 2011, 8:50 am
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Re: Front brakes pulsing...why?????

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

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post #6 of 32 Old Aug 18th, 2011, 9:58 am
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Re: Front brakes pulsing...why?????

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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post #7 of 32 Old Aug 18th, 2011, 10:15 am
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Re: Front brakes pulsing...why?????

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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post #8 of 32 Old Aug 18th, 2011, 10:20 am
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Re: Front brakes pulsing...why?????

Good one Ron

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post #9 of 32 Old Aug 18th, 2011, 10:46 am
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Re: Front brakes pulsing...why?????

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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post #10 of 32 Old Aug 18th, 2011, 11:04 am
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Re: Front brakes pulsing...why?????

Uh oh!

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/showthre...t=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.

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post #11 of 32 Old Aug 18th, 2011, 11:14 am
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Re: Front brakes pulsing...why?????

Quote:
Originally Posted by wa1200lt
Uh oh!

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/showthre...t=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!

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...


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post #12 of 32 Old Aug 18th, 2011, 11:30 am
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Re: Front brakes pulsing...why?????

I never knew that Ron. Thanks for the post.

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post #13 of 32 Old Aug 18th, 2011, 11:34 am
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Re: Front brakes pulsing...why?????

Quote:
Originally Posted by RonKMiller
.....end snip
The old wives - or in this case - the old bikers tale lives on...
Yes it does.

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

Loren

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post #14 of 32 Old Aug 18th, 2011, 11:35 am
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Re: Front brakes pulsing...why?????

Quote:
Originally Posted by RonKMiller
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!

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...
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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post #15 of 32 Old Aug 18th, 2011, 12:03 pm
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Re: Front brakes pulsing...why?????

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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post #16 of 32 Old Aug 18th, 2011, 12:14 pm
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Re: Front brakes pulsing...why?????

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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post #17 of 32 Old Aug 18th, 2011, 12:21 pm
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Unhappy Re: Front brakes pulsing...why?????

Too late.... They took the bait.

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post #18 of 32 Old Aug 18th, 2011, 12:26 pm
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Re: Front brakes pulsing...why?????

Quote:
Originally Posted by wa1200lt
Too late.... They took the bait.

I've been HAD .
Keep us posted peair. I'd be curious to know how it all turns out.
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post #19 of 32 Old Aug 18th, 2011, 12:36 pm
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Re: Front brakes pulsing...why?????

One thing for certain, if rotors don't warp humor surely does.... and don't call me Shirley.


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post #20 of 32 Old Aug 18th, 2011, 6:47 pm
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Re: Front brakes pulsing...why?????

Forget it ... deleeted

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post #21 of 32 Old Aug 18th, 2011, 9:53 pm Thread Starter
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Re: Front brakes pulsing...why?????

OK...I'm not asking to re-invent the wheel. I have the bike at a dealer, albiet not a BMW dealer because of where I live. The suggestions in this forum were given to him. I was hoping that a BMW owner would have experienced the same problem at some point and offered the obvious solution. The wheel is true as is the rotor as initially stat ed. I am aware that others have posted questions about the similar problem and don't want to start a 'knowledge war'. Thanks so much for all of the input. When I solve the problem, I will re-post.
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post #22 of 32 Old Aug 19th, 2011, 8:35 am
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Re: Front brakes pulsing...why?????

You talk about pulsing. Is the ABS unit kicking in even on light braking? Like someone said pull the relay for it and then you will know for sure.

Could it be one of the brake calipers is frozen and you then get uneven braking pressure and binding?

Being you have a 2000 I believe the front brakes have 2 cups per side. Are they put back in right and both moving freely.

Let us know what you find.

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post #23 of 32 Old Aug 19th, 2011, 5:23 pm
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Re: Front brakes pulsing...why?????

Quote:
Originally Posted by deanwoolsey
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.
Here's some excellent reading to describe what is going on.

It's the most concise "laymans" description I've ever come across. There are volumes of published SAE papers (that go into extreme minutiae and are excellent bed time reading since they are guaranteed to put you to sleep) and come to the same conclusion:

The "warped" brake disc myth

Correct pad and rotor bed in


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post #24 of 32 Old Aug 19th, 2011, 5:31 pm
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Re: Front brakes pulsing...why?????

Quote:
Originally Posted by peair
OK...I'm not asking to re-invent the wheel. I have the bike at a dealer, albiet not a BMW dealer because of where I live. The suggestions in this forum were given to him. I was hoping that a BMW owner would have experienced the same problem at some point and offered the obvious solution. The wheel is true as is the rotor as initially stat ed. I am aware that others have posted questions about the similar problem and don't want to start a 'knowledge war'. Thanks so much for all of the input. When I solve the problem, I will re-post.
There is no knowledge war. This is about getting your issue fixed. If you believe the mechanic where you've taken your bike, fine.

In my experience about 1 out of 100 are not knowledgeable about ANY issue, the other 99 will either completely bs you, make wild guesses or parrot what they've heard from other "expurts" that went before them. Most of these guys didn't even graduate high school...

Ask him if he believes if rotors can warp. If he does you need to find another mechanic.

Simple.


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post #25 of 32 Old Aug 19th, 2011, 6:07 pm
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Re: Front brakes pulsing...why?????

Ron, I don't think our positions really conflict. The author does cover both of our positions in his writing. As usual you have valid points, but it is possible for a rotor to warp (lateral runout) as the author indicates. I would grant you that the majority of the time the symptoms are likely caused by what you describe. To tell the truth, I never even considered measuring the thickness for variation as every issue I have ever seen was with lateral runout. That's always been my interpretation of warpage. I have never personally seen lateral runout on any of my motorcycles. Thanks for the new perspective.


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post #26 of 32 Old Aug 19th, 2011, 6:32 pm
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Re: Front brakes pulsing...why?????

Quote:
Originally Posted by JPSpen
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
There is a 3rd possibility and it is actually the most common - uneven buildup of pad material on the rotor. Sometimes this can be cured by several hard stops to really heat up the rotors and then let them cool without using the brakes.

http://www.stoptech.com/tech_info/wp...rakedisk.shtml

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post #27 of 32 Old Aug 26th, 2011, 10:29 pm
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Re: Front brakes pulsing...why?????

Ye gods I almost got a headache reading all the posts! As an ASE master tech for over 25 years I have seen many odd things involving anything with a motor that moves. I have pictures of vented brake rotors which have worn down to the point of only one thin slice of metal is left, razor sharp. We use the term 'warped rotors' because MOST of the public is not really up on studying brake issues, they simply want the dang thing fixed. Much like the term "tune-up" it is misunderstood and misused. When I hear 'tune-up" along with "check engine light" I know I have some explaining to do. My favorite customers? Bike riders!! Go figure....
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post #28 of 32 Old Aug 27th, 2011, 1:22 pm
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Re: Front brakes pulsing...why?????

Quote:
Originally Posted by RonKMiller
There is no knowledge war. This is about getting your issue fixed. If you believe the mechanic where you've taken your bike, fine.

In my experience about 1 out of 100 are not knowledgeable about ANY issue, the other 99 will either completely bs you, make wild guesses or parrot what they've heard from other "expurts" that went before them. Most of these guys didn't even graduate high school...

Ask him if he believes if rotors can warp. If he does you need to find another mechanic.

Simple.
ron
although i refuse to get involved in your rotor theory i do take offense to your comment about mechanics.... most if not all of us ARE knowledgeable on many issues. in the areas we are not knowledgeable in we can usually figure it out. please do not confuse mechanics with the latest generation of "technicians". as vehicles become more and more electronic and the desire to r&r instead of repair the need for a real "mechanic" becomes less and less.
ya i did graduate from high school.
oh you misspelled experts
thanks, john
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post #29 of 32 Old Aug 31st, 2011, 4:42 pm
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Re: Front brakes pulsing...why?????

Hi there!!!!
I am new in this forum, and I am writing from Venezuela, excuse my bad english.
I got the same problem of pulsing front brakes, so I was seeking the cause, and put my bike (K1200LT 2007) on her center stand and was checking the pads and calypers for any leaks.
I tried to lift up the front wheel by pushing a little the headligth up, and for my surprise all the front wheel came down. Thats when I realized too see that the Ball Joint in the LOWER FORK BRIDGE is complete broken and loose free, thats why when I used the front brakes, all the front wheel shaked like if it were pulsing brakes.
Take a look on your ball joint if it is loose or broken, maybe it is the worm that are you making nuts.


Best regards,

Anton Danzer
Maracay, Venezuela.
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post #30 of 32 Old Sep 1st, 2011, 9:22 am
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Re: Front brakes pulsing...why?????

Quote:
Originally Posted by drjohn55
ron
although i refuse to get involved in your rotor theory i do take offense to your comment about mechanics.... most if not all of us ARE knowledgeable on many issues. in the areas we are not knowledgeable in we can usually figure it out. please do not confuse mechanics with the latest generation of "technicians". as vehicles become more and more electronic and the desire to r&r instead of repair the need for a real "mechanic" becomes less and less.
ya i did graduate from high school.
oh you misspelled experts
thanks, john
It's not a "theory" like some dark matter blathering from Steven Hawking.

It is a well documented fact backed up by MANY, many technical articles published by SAE . - you know who they are, right? I'm a member, are you?

Well, I certainly agree with you about the new breed of "Technicians" and apologize profusely for lumping true mechanics in with them. I should have used the term technician in the first place. My bad.

I salute anyone that calls themselves a mechanic - since mechanics actually figure out why it's broken and know how to fix it! ..and if they don't know right off the bat they can usually figure it out. They also know how to fix it without first throwing a bunch of expensive parts at the problem.

It's kind of like the great Julia Childs. Everyone referred to her as a chef - and she despised the title. She preferred to be called a cook, since that's what she really did. And man, could she cook: MORE BUTTER!

My big issue is that the "art" of knowing how to actually fix things is being phased out of every aspect of our industrial society. "Just buy a new one or replace it" is how most problems are handled. Major corporations find it is easier and more expedient to buy failure prone products from China then to actually figure out how to improve the quality of their products. ...and boy howdy, is it EVER showing: Just this morning BMW cars announced a recall of 241,000 vehicles for a tail light issue. How hard is it for the Ultimate Driving Experience to engineer a tail light that works as expected?

BMW recalls 241,000 3-Series models over taillight failure

The GREAT news about all this is that there is a tremendous demand for well trained and experienced mechanics. You sir, obviously, are the exception to the vast majority and will have job security forever!

By the way, I misspelled expurts on purpose and put quotation marks around it. It's a play on words, kind of an extended metaphor. Never mind.

When I graduated from high school they taught me to start sentences with capital letters. Touche.


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Last edited by RonKMiller; Sep 1st, 2011 at 10:57 am.
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post #31 of 32 Old Sep 1st, 2011, 9:32 am
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Re: Front brakes pulsing...why?????

My new to me 2000 K1200LT came with pulsing front brakes - seems both previous owners used the brakes very lightly, last owner said he used front brake lightly not a fast driver, I've used the brakes my normal way and pulsing is slowly fading after 200 kilometers and some 130 kph HWY use, I also get a hissing sound from one of them I can only hear when wearing a 3/4 helmet - seems there was something deposited irregularly on one or both disks which is being removed by more vigourous braking - might take some sandpaper to them this weekend

Gary
2018 R1200RT
Past rides
2012 K1600GTL
2000 K1200LT
1992 K1100LT
2000 V Star 650/Velorex sidecar
1985 K100RT
1965 R60/2
1960 AJS 500 single
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post #32 of 32 Old Sep 1st, 2011, 11:00 am
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Re: Front brakes pulsing...why?????

Garnet only, please.

Vee vould not like to leave zee deposits behind for zee messin' uppin' again, Yah?


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