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Old 10-31-2012, 07:08 PM   #1
dirtspaz OP
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Eh? Grabby Brakes

I have a 2006 1200 GS with 90K miles. The front brakes are grabby and it gets worse at high speeds. The pulsation is definitely related to speed, as I slow down the pulsations slow down. The rotors are probably original and they do not appear to be warped and they do not appear to have any marks or scrapes beyond what is normal wear. I have cleaned the rotors with brake clean and installed new pads. Turning the ABS off has no impact. Any chance the rotors can be slightly machined and still be thick enough to use? Could it be something other than the rotors?
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Old 10-31-2012, 09:51 PM   #2
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There is another brake thread here with a similar subject. It was said brake rotors don't warp easily. Your problem may be variations in friction caused by holding a hot rotor with the brakes at a long stop light or similar situation. I think the solution was to try to sand the rotor with medium sand paper.
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Old 10-31-2012, 09:55 PM   #3
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I would guess your rotors are toast, especially with that much mileage. Not too many places that can machine bike rotors either. At least not in my neck of the woods. Just buy a low mileage used set or don't be a cheap bastard BMW owner and buy some new ones.
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Old 10-31-2012, 11:35 PM   #4
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My reply is kind of a combo of the two previous. The first thing is remove the rotors, get yourself an oscillating sander, and sand down all four surfaces really good with 220 grit sandpaper. Re-install, then clean your handprints off of all four surfaces. You can use brake cleaner, but Simple Green will work OK. Clean the pads again too.

If that doesn't work, then congratulate yourself on getting your OEM's to last for 90,000 miles ! That's pretty dern good.

Then treat your bike to some bling and get yourself some fancy new rotors.

BTW--you say the rotors do not appear to be warped. I'm not sure that's something that can be seen with the naked eye.
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Old 11-01-2012, 06:46 AM   #5
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Quote:
Originally Posted by scooteraug02 View Post
There is another brake thread here with a similar subject. It was said brake rotors don't warp easily. Your problem may be variations in friction caused by holding a hot rotor with the brakes at a long stop light or similar situation. I think the solution was to try to sand the rotor with medium sand paper.
This is always the first thing to try. The rotors can warp for sure, but often they are not.

Also, OP, check your rotor thickness. You might be getting close to needing new ones. The minimum thickness for the front is 3.5mm, and 4mm for the rear.

Jim
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Old 11-01-2012, 12:07 PM   #6
def
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Don't bother attempting to resurface rotors by machining them. There is really no way to chuck them in a lathe.

The traditional cast rotors found on automobiles are turned on a lathe and a new surface is exposed by cutting away some of the rotor stock. This is not possible on motorcycle rotors. First, the rotor is already very thin compared to an auto rotor and if you were to attempt to cut the rotor, it would deflect and make a mess.

Motorcycle rotors are blanchard ground to be parallel and true at time of manufacturer.

As mentioned, a light rotor sanding to remove brake pad residue from hot clamping the front brake is about the only maintenance you can perform on the rotor.

As suggested, check your rotor thickness. You may be at or near the limit requiring new rotors.

I buy all my brake parts from these folks. Their prices are very good and they know their stuff.

http://www.cyclebrakes.com/html/ebc_brake_rotors.html
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Old 11-01-2012, 09:18 PM   #7
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After 50,000km my front brakes were pulsing, felt worst at lower speeds. Finally got the techs to have a look at the 60,000km service, apparently the rotors vary in thickness (hence the issue).

BMW wouldn't cover because of mileage (heck, you may as well try some goodwill), stuffed if I'm replacing already, so I'll live with it until 100,000km ish (unless they don't last that long), and then replace.

As suggested, I've read that stopping with the front brake on can cause the issue, so try not to, or come to a stop, release the brakes and roll forward or back a bit.

I've just toasted my second set of BMW rear pads in 20,000km (first set lasted 40,000km). You win some, you lose some...
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Old 02-02-2013, 08:32 PM   #8
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What about popping them into a surface grinder and taking a thou or two off each side?

Also, don't forget to keep an eye on head bearings, the pulsing has a tendency to loosen them up.
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Old 02-02-2013, 10:15 PM   #9
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Quote:
Originally Posted by KMC1 View Post
What about popping them into a surface grinder and taking a thou or two off each side?

Also, don't forget to keep an eye on head bearings, the pulsing has a tendency to loosen them up.
Though possible, this is not usually an issue on a telelever.

As for surface grinding, that is possible, but beware, there isn't much extra material to play with.

Jim
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Old 02-02-2013, 10:17 PM   #10
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By the way, the pad build-up issue on the rotors is much more common with the servo-ABS because the brakes clamp damn hard at stops with little hand pressure. This is also why the get grabby when the pad material transfers to the rotors.

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Old 02-03-2013, 07:40 PM   #11
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Oil on rotors

I read a tech response to a reader with a similar problem (...in one of the major motorcycle mags Motorcyclist or Cycle World)

The magazine tech guys said that fork oil on the rotors can be "baked" in to the metal surface via friction of the brake pads. This produces patches of rotor where the friction properties differ. Thus, grabby brakes. The story was about a guy who took his bike in for maintenance, and then a bit later, his brakes were grabby.

Of course, this may not be the case with your bike, but it is a possibility.
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Old 02-20-2013, 02:49 PM   #12
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For me, it was an out of truth wheel that provoked the pads to deposit unevenly on the disk, and eventually resulted in pulsating brakes.

From what I understand of the process, badly scalloped tires would have the same effect.
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