Originally Posted by
Maquilina
I've been dealing with a similar problem with my trek checkpoint alr5 for almost a year now. Your description is almost exact to my experience. Going down a hill if I brake and hit a bump in the road while braking, the front wheel goes into considerable vibration and braking power severely impaired until I release the brake and reapply the brake. On smooth roads I never have a problem.
I have changed the disc brakes and pads. This did not fix the problem. I thought maybe there was a problem with the forks. I replaced the forks and again this did not solve the problem. I'm wondering if this is a design problem.
Did you manage to get to the bottom of your problem?
By the way, I am quite a light weight person (70kg). I don't think being heavier is the issue either.
That does sound like a resonance issue. Hitting a bump under braking is probably the trigger for the resonance, which will then tend to amplify until you release the brake and re-apply.
The hard part is finding out what component is actually resonating. It sounds like you’ve changed most of the obvious parts, but what about the front wheel?
You could also try taping a few small lead weights to suspect components like the forks and see if the vibration goes away because of a change in the resonant frequency. Tyre pressure might also have an effect.
As I mentioned much earlier in this thread, I had a mountain bike that was prone to rear brake resonance through the rear chain stays when the pivot bearings were worn. Bumpy descents would trigger the resonance much more than braking on smooth surfaces, which made it a pain to diagnose.