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One of my Formula 'The One' calipers isn't auto-adjusting for wear. That is, the pistons retract fully when there is no disk or pads in place.
It appears that fluid from the reservoir isn't topping up the brake hoses.
Can anyone suggest where the blockage is, or how to tackle it?
Thanks.
Can you describe what is happening when you apply the brakes when riding?
The auto-adjusting mechanism relies on some friction between the pistons and the caliper seals ( https://textar-professional.com/textar-training-center/brake-piston/ ); if that interface is slightly worn or overly lubricated, the vacuum created by the main cylinder spring will always fully retract the pistons, instead of pulling additional fluid from the reservoir.
Changing the caliper seals should fix the issue.
No riding, it's in the workshop, a new build from old parts.
Brakes haven't been used for a while, one piston wasn't retracting so I was cleaning the pistons.
Symptoms of the issue were that with the pads out, I could squeeze the brake lever; the pistons would go in. Release and they'd retract to their original position.
<span style="font-size: 0.8rem;">What's supposed to happen is that when the lever is depressed far enough, fluid should be drawn from the reservoir to the hose and caliper to top them up. The next time the lever is pulled the pistons start from further in, taking up pad wear. </span>
My guess is that the connection from the reservoir is blocked. Anyway after pushing the pistons in and out, and cleaning them, the mechanism came back to life, so whatever was causing the problem is out of the way.
I'd be interested if anyone can suggest how to deal with this should it happen again. Possibly just a change of brake fluid. Or strip the levers down...
My guess is that the connection from the reservoir is blocked.
There is an easy way to test out this theory by trying to bleed them: if you can't push brake fluid from/to the reservoir syringe, your assumption is correct.
I'm not sure which version of The Ones you have, but on my old R1s the reservoir cap was non-detacheable (silver cap on the inside of the clamp). At one point the reservoir bladder underneath went bad, so they started seeping brake fluid through the breather hole, that's when I moved on to Shimano...
There is an easy way to test out this theory by trying to bleed them: if you can’t push brake fluid from/to the reservoir syringe, your assumption is correct.
The auto-adjusting mechanism relies on some friction between the pistons and the caliper seals ( https://textar-professional.com/textar-training-center/brake-piston/ ); if that interface is slightly worn or overly lubricated, the vacuum created by the main cylinder spring will always fully retract the pistons, instead of pulling additional fluid from the reservoir.
Changing the caliper seals should fix the issue.
I was going to suggest the standard full bleed and if not resolved a calliper piston seal replacement.
After cleaning and greasing the pistons with silicone, one at a time by depressing one to push the other out, then a bit more pumping the brakes, they finally started to auto-adjust.
Possibly some problem with the seals which use, or silicone helped to clear.