Not warped discs but pulsating brakes!

My 04'r1150r w/ 30k mi has had the pulsating front brakes since roughly 10k mi. They smooth out sometimes and last for days with no pulsation, then all of a sudden they start pulsating again. I have tried different braking techniques and found no combination that total alleviate the problem. I'm wondering about the spring washers that keep the disk aligned?

One thing to consider. I have the same problem on my RT. Some days it's worse than others. I took it to a very good independent BMW shop thinking the rotor was warped. He checked it for runout and warp with a micrometer and it was better than a new one. After the mechanic rode the bike, he thought it was uneven wear of the tires and the variation in pulsation depends on the inflation at the time. He didn't feel it posed any danger to ride it. He suggested riding until the tire needs replacing and then see if it fixes the "problem".

Another cause is oil on the rotor.

If the rotor is true within specs then brake pulsing is usually caused by an area on a disk with greater or less friction. It is sometimes caused by contamination on a disk and sometimes caused by deposits left by the brake pads. A good thorough cleaning of the brake disk - brake cleaner works but I prefer to hand scrub carefully with a cloth damp with paint thinner followed by an alcohol based brake cleaner.

awagnon said:

He checked it for runout and warp with a micrometer and it was better than a new one.

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You mean a dial indicator. All you can do with a micrometer is check spot thicknesses.

Back to checking run-out. If he did use a dial indicator, how did he get a valid reading if the discs aren't solidly riverted to the carrier? Just about all brake discs are floaters nowadays.

bransan said:

I'm wondering about the spring washers that keep the disk aligned?

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The wave washers are there to take up the slack, AFAIK. On a race bike with real floating discs, the discs rattle when just pushing the bike around. Your average owner would complain if they had to listen to that.

The disc fasteners have shoulders to provide the determined gap. They also use a circlip on the fastener to add a bit of friction, while still enabling the disc to move.

GlobalRider said:

If he did use a dial indicator, how did he get a valid reading if the discs aren't solidly riverted to the carrier? Just about all brake discs are floaters nowadays.

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He appeared to be using a dial indicator for runout and a micrometer to check for uniform thickness to the best of my knowledge. I didn't watch him the entire time, so I don't know how he allowed for the floating disk. Just said it was within specs and not warped or worn unevenly. I trust him to know what he's doing since he's a BMW certified mechanic with more years wrenching than most have riding. Maybe Paul will come back with how he checks for a warped rotor. I can't answer your question.

Does the ABS Modulator sound change when the pulsing occurs??? If it does check the gap between the sensor and the sensor wheel. Maybe the ABS sensor is marginal or there is a slight warp in the sensor wheel.

I fixed the pulsating brakes on my K75 by replacing the front wheel bearings.

I had the same thing on my RT a few months ago. Someone suggested to me it was just the brake pads... I thought that was silly. I ended up buying new rotors and kept my existing pads since they were about 80% still. I was surprised to find the problem followed to the new rotors.

I put new pads on the following day and 10k miles later the problem hasn't returned.

Just for giggles I bought my original rotors to my friends machine shop and he verified they're true.