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Discussion Starter #1
Hi all - In the middle of an epic trip two summers ago, my front brake started stuttering. I can't point to any particular moment or incident that might have caused it. It is chafing at a certain point in the rotation of the wheel. I notice it most when slowing to a stop. Chunk, chunk, chunk...chunk...chunk......chunk......stop. The brakes are functional, just not smooth. It looks to me like the rim is spinning true. I took off the rotor and it appears perfectly flat all around when I check it with straight edge laid across. I tried a different axle. No change. Any suggestions?
 

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Do you have the original rubber brake line? I had a similar problem, replaced the rotor and pads, and the problem was still there. I eventually installed a stainless steel brake line and new MC and the problem went away. My guess is that it was in some sort of bulge in the line.
 

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Discussion Starter #4
Pads looks clean and evenly worn. Plenty of life left. Thanks for the tip, Schmitty. I will investigate the lines and MC.
 

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Sounds like a brake line aneurism.................
 

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Discussion Starter #7
A year later and I've finally found the time to replace the master cylinder and install a new stainless steel brake line (in addition to a triple bypass!). Front brake is firm and responsive, but still the jitter/wobble when braking. I can feel it pulsing at the front brake lever. Next step is to make sure the rotor is totally true (sure seems like it) and mounted flush (I'll remount it). Any way the caliper could be to blame? Seems like there would be a consistent rub if the caliper was gripping, rather than a pulse with wheel rotation.
 

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If the caliper is not "floating" freely on the pins, it can cause the sensation that you feel when braking.
 

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In my case it was a bent rotor. Replaced with another and the problem want away.
 

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Discussion Starter #10
Thanks, OCR. That seems to have got it. The caliper slide pins still had grease on them and appeared to be moving freely, but I cleaned them up anyway and regreased with synthetic caliper grease. Braking is much smoother now and holding steady after a few hours riding.
 

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Discussion Starter #11
aargh. Guess I was eager to call it good, but... still pulsing. It did seem to be better at first after cleaning up the caliper pins, but I think I may have also been leaning more heavily on the rear brake than usual, masking the front brake pulse, which is still quite pronounced when using the front brake only, especially during the last few rotations while braking to a stop. Seems like the next move is to try a different rotor, even though the current one sure looks to my eye to be rotating perfectly true.

There was a small bit of rust on the caliper piston (outer edge that contacts the pads and inside the cup). I could rebuild the caliper, but aren't the typical problems with that either leaking or sticking/gripping (rather than the pulsing with wheel rotation)?
 

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Discussion Starter #13
So far: new master cylinder, new steel braided brake line, completely rebuilt caliper, new pads, tried a different rotor (ebay). The brakes are still pulsing with wheel rotation while stopping. Both of the rotors I have seem to be perfectly flat: I placed one on top of the other and spun them around and the flat surfaces mated seamlessly. I have been careful in seating/bolting the rotors in the hub. What else? I know the wheel rim is not perfectly true, but that shouldn't impact the rotor?
 

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Discussion Starter #15
Isn't your rotor bolted directly to the wheel?
Sure, to the hub of the wheel. I assume it is the outer wheel rim that is bent a bit which doesn't seem like it should impact the centering of the rotor. Guess I won't know for sure unless I try a brand new rotor and/or wheel.
 

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Discussion Starter #16
Resurfacing the rotor fixed it. I had it done by Tom at TrueDisk. The pulsing has vanished. Lesson learned: A rotor axial runout/variance of fractions of a millimeter is enough to induce pulsing.
 
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