When on the I brake I get a pulsating feedback on my rear brake lever. I checked to make sure the wheel is true, and also the dish, which is ok.I re-checked the torque on the caliper bolt and adjusted it to 9Nm. The tire also has no bumps that I can see or feel. Any ideas?
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1Could you elaborate a bit more? Are we talking about a disk or rim brake?– Benedikt BauerFeb 8, 2015 at 18:34
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Checking the wheel is true + caliper bolt sounds like a road bike.– HollowayFeb 8, 2015 at 18:44
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sounds like you've done a lot. Is the braking surface clean?– PeteHFeb 8, 2015 at 20:31
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Like on a car, pulsation means that the "disk" is warped or uneven somehow. Of course, depending on the bike, the "disk" may look a lot like a rim, but same difference. If you have rim brakes, the pulsation means that there's a spot where the rim gets wider or narrower than normal. (If you have disk brakes the disk is shot.) (The one exception to this is if some sort of goo has gotten on the braking surface, in which case cleaning it may solve the problem.)– Daniel R HicksFeb 9, 2015 at 0:51
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And note that one reason for a rim to become uneven is that the braking surface is worn through to the point that the rim is beginning to fail. If allowed to continue, such a rim can fail rather catastrophically.– Daniel R HicksFeb 9, 2015 at 1:10
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2 Answers
After the discussion in the comments, I suspect that the rim is deformed.
This can happen if you hit a pothole or kerb too hard, especially if the tires are not pumped up hard.
If the rim is deformed then you may be able to see patches where the brakes have worn the rim more. It's the brakes grabbing on these that create the feedback you are feeling.
There is not much to be done about it. Some people try to straighten them using a wooden mallet, but the success rate is low. Often the wheel is worse rather than better.
To avoid this kind of damage in future try to get your weight off the wheel as it hits the bump, by getting out of the saddle and moving back as the front wheel hits, then moving forward before the back wheel hits.
A rim worn down from age through braking may shudder. In my experience the rim shuddered more when the tyre was more highly inflated.
This can be tested by clamping the brakes on the bicycle, and turning the wheel to detect uneven deformation when the brakes grip excessively at particular points.
The deformation in this case will not be immediately obvious to touch or sight. After testing with the brakes, the deformation should appear as a spreading of the rim at the most worn section.
In this circumstance the rim will need to be replaced, involving rebuilding the wheel.
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This case can be tested by placing a straight edge radially across the rim. Wear will be seen as a groove in the rim. More than about 1mm wear puts the wheel at risk of collapse.– andy256Feb 9, 2015 at 1:22
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I did the straight edge test, and at one point on the rim, there was a change in the area under the straight edge, from a straight line to a convex one. Thankfully I purchased the rims with a replacement warranty and right now the rim is being looked at by the manufacturer. Thanks for the help.– JulesFeb 22, 2015 at 12:33