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Old 01-23-2013, 05:15 PM   #1
Dadd OP
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Question Pulsing front brakes

So, on three BMW's over the years, (R1100RT, R1200RT and R1200GS) I've developed, to varying degrees, a pulsing feeling in the front brakes on each bike. Usually it's most distinct at low speed, nearly at a stop, but it's somewhat evident at all but high speed braking. I've mic'ed the front rotors on my current GS, and they vary in thickness by about .005". Haven't checked for warpage with anything but an eyeball, but warpage seems like it would tend to open the calipers and cause a loss of braking force, and that's not happening.

Question is this: Anyone else had this problem, or found a cause? Is it something I'm doing? Seems unlikely, but (of course) BMW says it ain't their fault/normal wear/not warrantied. Can't imagine that brake pad compound choice would wear the rotors unevenly. I probably do sit at stoplights with the front brake lightly engaged, but don't we all? Do dey all do dat?
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Old 01-23-2013, 05:29 PM   #2
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Quote:
Originally Posted by Dadd View Post
Question is this: Anyone else had this problem, or found a cause? Is it something I'm doing?
Usually it happens from brake pad buildup on the rotor. When the brakes are hot, you stop and hold the front brake on material transfers on too the rotor.
A light sanding of the rotor should fix the issue.

Is your rotor in spec?

Front disc thickness: This is for an 05 but I think they are all the same
Standard……..4.5 mm
Service limit…4.0 mm
Runout Service limit…..13mm
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Old 01-23-2013, 05:34 PM   #3
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Quote:
Originally Posted by Mudcat View Post
Usually it happens from brake pad buildup on the rotor. When the brakes are hot, you stop and hold the front brake on material transfers on too the rotor.
A light sanding of the rotor should fix the issue.

Is your rotor in spec?

Front disc thickness: This is for an 05 but I think they are all the same
Standard……..4.5 mm
Service limit…4.0 mm
Runout Service limit…..13mm
Earlier models (oilheads) typically are 5.0mm new and 4.5mm min with .003" max runout.
Check your model specs. to be sure
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Old 01-23-2013, 05:35 PM   #4
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Quote:
Originally Posted by Mudcat View Post
Usually it happens from brake pad buildup on the rotor. When the brakes are hot, you stop and hold the front brake on material transfers on too the rotor.
A light sanding of the rotor should fix the issue.

Is your rotor in spec?

Front disc thickness: This is for an 05 but I think they are all the same
Standard……..4.5 mm
Service limit…4.0 mm
Runout Service limit…..13mm
Re: rotors
Earlier models (oilheads) typically are 5.0mm new and 4.5mm min with .003" max runout.
Check your model specs. to be sure
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Old 01-23-2013, 05:52 PM   #5
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had the same problem

I have had the same issue with my 2008gsa since it was new . Turns out in my case I have been able to fix it every time by taking the front wheel off and cleaning the circular springs that allow the disc to float. I work the disc around a bit and when I reinstall the wheel the problem is gone. I think the dirt and sand that builds up in the spring s keep the disc from floating.
Hope this helps
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Old 01-23-2013, 07:22 PM   #6
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I have the same issue on my 1150, new rotors, pads, washers, sanded the disks, measured the runnout, I even milled the 10 mounting pads flat and added a thin washer underneath. I really think they run true but still pulse!
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Old 01-23-2013, 07:40 PM   #7
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Mudcat has it right. Disc brake shudder as it is often called, is the result of hot stops using the front brake excessively then, holding the bike at rest with the front brake, say at a stop light while awaiting the light change. This causes a transfer of some of the friction material binding agents in the hot pads to transfer to the cooler rotor.

Now, you are left with a rotor with varying coefficients of friction across the area swept by the friction pads. This causes the shudder you experience.

Race car drivers are especially cognizant of this phenomena and adapt their braking techniques to minimize it.

Proper brake pad friction material can minimize the problem. The best option is when making a hot stop, release the front brake as you come to a stop and use the rear brake to hold the bike at rest.

This braking technique is taught as part of the MSF basic course.

Sanding the rotor is the only remedy I am aware of that works.
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Old 01-23-2013, 09:00 PM   #8
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The above worked for me, had the same issues on a 1150GS. Riding hard with lots of heavy braking would clear it up. Clamping on the pads at a stop would bring the condition right back.
The pads act like a heat sink and slightly warp the rotors as well as deposit pad material on the rotor.
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Old 01-24-2013, 12:31 AM   #9
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I have the same problem on my '09. Is there a preferred procedure to sand the front discs?
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Old 01-24-2013, 01:09 AM   #10
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Originally Posted by Motor2of7 View Post
I have the same problem on my '09. Is there a preferred procedure to sand the front discs?
Sand it until it's clean. No need to change the width of the rotor with sand paper.
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Old 01-24-2013, 03:49 AM   #11
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Quote:
Originally Posted by Mike Ryder View Post
The pads act like a heat sink and slightly warp the rotors as well as deposit pad material on the rotor.
I believe, Sir, that it is the other way around.
That is, the heat can not escape.

Remember, the pads are hot too.

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Old 01-24-2013, 06:52 AM   #12
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100 THREADS all GS/GSA owners should read.

12. WHY ARE MY BRAKES SO GRABBY?
http://advrider.com/forums/showthread.php?t=838082
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Old 01-24-2013, 07:49 AM   #13
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Quote:
Originally Posted by tagesk View Post
I believe, Sir, that it is the other way around.
That is, the heat can not escape.

Remember, the pads are hot too.

[TaSK]
Brakes convert the rotating energy in the wheel to heat using friction. This heat is then wasted as the rotor radiates the heat into the atmosphere. The heat energy flows in the direction of hot to cold. The pads are hotter than the cooler rotor (remember, it has been rotating in the breeze) and so the pads use the rotor as a heat exchanger or radiator.

When the heat is extreme such as when coming to an abrupt stop from high speed, the friction pad is overheated. If the pads are hot clamped to the rotor at rest, some of the binder in the friction pad is deposited in one area of the rotor causing the variations in COF across the total area of the rotor resulting in the brake shudder we are talking about here.

Its simple; Avoid hot clamping your front brake when at rest.
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Old 01-24-2013, 07:59 AM   #14
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Sand it until it's clean. No need to change the width of the rotor with sand paper.
When sanding the rotor, you are merely modifying the rotor surface. You are not attempting change the rotor dimension or remove rotor material. I would use say 320 grit. Sand until you have a new surface appearance, no more. It is OK to lleave it rough in appearance. When doing this, I also remove the brake pads and rough them on flat concrete so they too have a fresh surface. Finally, clean the fresh rotor surface with brake cleaner and a clean rag. Subsequent applications of the brake will bed in the brakes as if new pads and rotors had been installed.
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Old 01-24-2013, 04:41 PM   #15
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Thanks

Lots of good advice. I'll give sanding a shot. Thanks a lot.
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