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  1. #1
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    Having trouble with promax q3 hydraulic disc brakes. Feels jittery when braking

    I bought a GT Chucker 2.0 about 4 months ago. It has hydraulic promax q3 disc brakes. I have been having problems with the brakes since I got the bike. The rear brake feels very jittery or rough when I brake hard, I am not locking the brake, but enough to get top braking power.

    I tried braking them in, but still have been having the problem. I tried adjusting them, and noticed the washer on the brake adjusting bolt is very close to the disc, when I adjusted the brakes it would cause the disc to rub against the washer. I had to readjust so the washer would not rub, unfortunately I still had the problem.

    I tried spraying some simple green cleaning solution on the disc and in the pads and this seemed to fix the problem, but only for a little while and it goes back to being jittery when I brake hard.

    Next I took the brakes apart and used sandpaper to try and wear them down(after calling nashbar and was told some oil could be causing the problem). I also sprayed simple green cleaning solution. When putting the brakes back I was again getting a problem with the washer rubbing against the disc, I used a grinder to grind down the washer, but the washer still slightly touches it. Unfortunately this still did not fix the problem.

    My dad has been helping me with all of this and he has been rising for 20 years, he told me the caliper isn't fully retracting. Could this be a cause of the problem? Could it mean the calipers are not straight?

    I called Nashbar whom I purchased the bike from, they said I could mail them the part and they would either fix it or replace it, but it will take a few weeks and I dont want to be without my bike, so I want to make sure this is the problem.

    Is there a way to check if the caliper is warped or off? Could it be that the disc is warped? If so how do i check?

    edit: I have been getting help with the guys at nashbar and they said i may need to bleed it. I have a hayes bleed kit anyone know if I could use this on my promax q3s?
    Last edited by tooquick; 08-08-2011 at 12:16 PM.

  2. #2
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    I've found with certain brake systems, if the rotor has very aggressive cutouts it can cause a pulsating sensation. I had issues with certain models at the shop I worked at and the easiest solution was to replace the rotors, I used the old school shimano style rotors that are drilled out and voila pulsation gone.
    I don't wear a helmet, I wear a turban protector!

  3. #3
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    thanks peedrama, will give it a try. You are probably right on, since the rotors do have aggresive cutouts. I just sent the brakes in to nashbar to get them fixed though, hopefully they can correct the problem with them not retracting

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