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Disc brake dragging

Old 07-01-19, 01:44 PM
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Skipjacks
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Disc brake dragging

I just replaced hydraulic disc brake pads. My previous pads were dragging slightly, causing resistance on the front wheel.

I got new pads, cleaned the calipers, made sure the pistons were properly cleaned, seated the caliper properly so there was no drag when I free spun the wheel. Everything was great. Took it out for a 5 mile test ride. Everything was fine. The front wheel still spun freely with no drag on the brakes.

The alignment procedure I used was to loosen that caliper, clamp down on the brakes hard, then tighten the caliper bolts while the brake was engaged.

I rode the bike to work today and the drag is back. I spin the front wheel and it stops pretty quick because one of the pads is dragging on the rotor.

Rotor is true. It's a steady drag, not just on half of each rotation.

It's only 1 side that's dragging, not both.

I thought all this was fixed when I cleaned everything and put in new pads. I really thought it was fixed after 5 miles when it all worked well. But this morning's additional 3 miles and the same problem I had with the old (very worn out) pads is back.

I'm out of guesses and things to check.

Any ideas? Best I can think of is to redo the calibration and tighten the bolts down harder this time. Maybe the caliper shifted due to a more rigorous rider than I did on the test ride.

Last edited by Skipjacks; 07-01-19 at 02:09 PM.
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Old 07-01-19, 10:23 PM
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Most of the time the "pull the lever and tighten the bolts" method works fine and sometimes it doesn't. One thing you can try is do it again and put a business card between the pad a rotor on the side that rubs to shift the caliper over a hair. Other than that there is always eye balling it.
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Old 07-01-19, 10:58 PM
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Is this quick-release or through-axle? If it is quick-release, get some good internal-cam skewers, or your wheel will tend to move around slightly in the dropouts.
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Old 07-02-19, 01:55 AM
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probably a sticking piston check to make sure they are both retracting
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Old 07-02-19, 05:53 AM
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I find that the method of holding the brakes and tightening the caliper doesn't work very well unless you are really careful in tightening the bolts in small increments. Tightening one, while the other is still loose, causes the caliper to twist and the rotor is not stiff enough to prevent it.

In this case, it appears that you had the caliper centered and the pistons advanced at different rates. I suspect that one of the pistons is stuck and the other has advanced further to compensate. You should be able to see that only one piston is working, if you pull the lever and watch the caliper. The good piston(probably the side that is rubbing) will advance and flex the rotor over to touch the other pad.

I just had to replace a Shimano caliper that was having the same issue. It turns out that a small piece of the piston had broken off and was causing the piston to cock at an angle and get stuck.
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Old 07-02-19, 06:06 AM
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Those mentioning a stuck piston are in the right track.

Centering the caliper isn't enough. The pistons have to be reset - completely retracted into the bore.

https://www.epicbleedsolutions.com/r...liper-pistons/

Try it again. Reset the pistons, center the caliper and if it still drags then there might be a sticky piston. A piston which does not retract might be visible with the bike on the stand and a headlamp.


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Old 07-02-19, 07:02 AM
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So I redid the 'calibration' thing and really wrenched down the bolts tightly, making sure to do a little on each bolt at a time so they tightened evenly.

I've ridden about 8 miles since that and the wheel is still free spinning properly.

So I might just have not tightened the caliper bolts properly the first time.

I don't think it's a sticky piston because I cleaned it well and moved the piston in and out a few times while cleaning to make sure it was compressing and retracting properly. Also the side that was dragging this time is the opposite side from the one that was dragging before the brake change. That side definitely had a stuck piston that cleared up when I cleaned the whole system. And it's working fine now.

I think I just did a crappy job of tightening the caliper bolts the first time.
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