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Heavy rhythmic vibration whilst braking...

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Heavy rhythmic vibration whilst braking...

Old 07-09-13, 02:29 PM
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Ithaka
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Heavy rhythmic vibration whilst braking...

I just purchased a very nice condition '07 Giant OCR C2, with Ultegra everything and Shimano 550 something wheels. The only problem I'm having is a bad vibration when the front brake is applied. The wheel is true, because the brakes are about as well adjusted as they possibly could be, and there is no rub, and I have failed to find any defect in the general shape of the rim and the braking surface. Does anybody have any idea why I'm getting heavy, rhythmic vibration during braking?
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Old 07-09-13, 02:35 PM
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I would bet the rim wall has a bulge or indent in it somewhere. Does braking increase or decrease with the thump? This will tell you lots. Also, might check to make sure that the brake attachement bolt is tight as are the pivot bolts. But the rythmic part to me would be a rim issue. Could also be a rim seam. Trying taking the front wheel out and flipping it so QR handle is on other side to see if this makes the problem go away. If is does, it could well be a rim seam that is not flush and is catching on the brake pads.
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Old 07-09-13, 02:54 PM
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Is there any brake pad/road schmutz build-up on the brake surfaces of your rim? I had a similar issue and was able to resolve it by cleaning the braking surfaces to ensure that they are absolutely clean. I used Brasso metal polish and super fine steel wool. If you do use a metal polish be sure to remove all residual residue and rinse well with water. After the rim is dry wipe it down with rubbing alcohol. Reface your brake pads with sandpaper (or replace with new ones - if they are the originals they may be dried out). This worked for me.
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Old 07-09-13, 03:00 PM
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Are these the original Mavic Ksyriums? Or are they different? If it's a welded joint, then you may need to spend some time with abrasives on the sidewall to condition the surface. I'd be surprised if they were the originals and wonder if the front wheel has gone through some trauma and been re-straightened and rebuilt. Hopefully not. One thing to try is to flip the front wheel around (remove the skewer, rotate, put skewer back in). Yes, the label will be reversed and not on the same side. Now ride and brake. Does the same rhythmic vibration continue or is it better?
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Old 07-09-13, 03:08 PM
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I've had a rim that pulsed while braking, due to a variation in the rim width. I had to use a micrometer to measure the rim, in order to find the high and low spots. This was a brand-new high dollar Campy Eurus wheel, with machined braking surfaces. Fortunately, the pulsing was only apparent during light braking. With a little harder braking, the pulsing went away, so it was tolerable.
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