How To Clean Hydraulic Brake Pistons - Tech Tuesday #104

What people said

Recommends Argenti Apparatus · 2018-05 · Bicycles Stack Exchange · on “Quad QHD-4 Axis Disc Brakes stuck (can't push open)”

You pretty much have nothing to lose by disassembling the calipers and attempting to free the pistons. They are useless now, so if you break something it does not matter. You may try contacting the manufacturer (Hayes?) and asking if they have a service manual. The silver cap with the Torx socket does seem to be the way into the internals. If you can measure the point-point distance with some accuracy (1/10 mm) you can look up what size it is. The Wikipdia page on Torx drivers [LINK] lists the sizes. If not, take a caliper to the tool store and try different sizes until you get the right one. It's the inboard piston that is stuck so if you can take the outboard one out you should be able to

Recommends Argenti Apparatus · 2019-01 · Bicycles Stack Exchange · on “Avid Juicy 3 brake piston problems”

You absolutely should not have let fluid out of the system. If the brake was working before there was not too much fluid in the system. You will need to bleed the brake to remove air bubbles and restore the fluid level. (If the back brake has not been bled in eight years you should do that one too.) Dirty pistons and seals are usually to blame for non-retracting pistons. In extreme cases the whole caliper has to be disassembled and cleaned. You can try to find the manual for Avid brakes by searching on the SRAM website [LINK] . There is a 2006 manual [LINK] which may apply. Check out this Park Tool video for how to clean hydraulic brake calipers. It also explains how piston retraction and ad

Recommends Argenti Apparatus · 2019-03 · Bicycles Stack Exchange · on “Constantly engaged disc brakes, how hydraulic brakes retract?”

Hydraulic brake pistons are actually retracted by the rubber seals. The seals are deformed slightly as the piston advances, then they re-form to provide the retraction force. This works because the retraction distance is actually very small. The seals design also allows piston advancement to take up pad wear. As the pads wear the piston moves slightly beyond the deformation limit of the seal and slips through it a small distance. There is a good Park Tool video that shows how this works [this video] . I would definitely be concerned that holding the brake on for a long time would affect the rubber seal. What might happen is the seal will slip back on the piston while it is pressed up against the

Recommends Argenti Apparatus · 2020-01 · Bicycles Stack Exchange · on “Disc brake just a little too tight”

There is no adjustment for piston position on hydraulic brakes. Hydraulic brakes have a built in mechanism to retract the pistons slightly when the brake lever is released. The pistons are mounted in flexible rubber seals that deform as the pistons are pushed forward. The seals then pull the pistons back as fluid pressure is released. The pistons also slip through the seals to automatically advance as the pads wear. What you need to do is adjust the calipers with the pads advanced up to the rotor. If you push the the pistons back and adjust the caliper position you wont be able to align the pads accurately enough. A good trick is to loosen the caliper bolts, then hand tighten them so the cal

Recommends Argenti Apparatus · 2020-01 · Bicycles Stack Exchange · on “My front disc brakes are rubbing despite my efforts”

It sounds like your pistons are failing to retract when the brake lever is released. The mechanism used in bicycle hydraulic brakes to advance the pistons as the pads wear and to retract the pistons slightly when the brake lever is released is flexible rubber seals that surround the pistons. The seals deform as the pistons are pushed forward then pull the pistons back as fluid pressure is released. It may be that your seals or pistons need cleaning. Check out this Park Tool video that shows how the seals work and how to clean them.

Recommends Tom Anderson · 2020-02 · Bicycles Stack Exchange · on “How do self-adjusting hydraulic disc brakes work?”

There's a nice illustration of how a piston moves in its seal in this video from Park Tool [this video] . It doesn't explain what's happening at the master cylinder, though!

Recommends Argenti Apparatus · 2020-04 · Bicycles Stack Exchange · on “Brakes QHD-6 Tork - how to fit new pads”

If the brakes are stuck you likely need to do more than replace the pads. The pistons are probably stuck in the caliper due to dirt build up or corrosion. Park Tool has a good video [this video] on cleaning pistons and unsticking them.

Recommends Argenti Apparatus · 2020-07 · Bicycles Stack Exchange · on “Should I replace my disk brake calipers?”

What you describe in the first part of your question is normal. Longer lever travel may indicate you need to bleed the brakes. Uneven caliper piston movement is caused by contamination of the piston seals with dirt. Park Tool has a video about cleaning pistons and seals [this video] . However this is bit more worrying: Sometimes the pistons are cock-eyed, extending from the caliper at an angle. Sometimes I notice air bubbles in the lube oil between the pistons and the caliper. The pistons should not be able to extend at an angle. That's not 'lube oil' between the pistons and caliper, it's the hydraulic fluid (mineral oil in Shimano's case) and you should not be seeing any of it getting past the s

Recommends Grigory Rechistov · 2020-08 · Bicycles Stack Exchange · on “Shimano Deore hydraulic brake problem”

To add to other answers, there is a great video by Park Tool published recently, explaining the hydraulic brake pistons. They explain accidentally blowing them out as well as their cleaning process. Prevent "sticky pistons" by cleaning and lubing the pistons every time you change pads. We talk a bit about how the brake functions and walk through the cleaning procedure to help your brakes in the long run.

Recommends Argenti Apparatus · 2020-11 · Bicycles Stack Exchange · on “Formula T1S disc brake rub”

Seeing the pistons extended a little is expected on hydraulic disc brake calipers. As the pads wear fluid is slowly drawn from the reservoir and the pistons extend to take up the space left by the pad wear. The pistons should retract slightly when the lever is released to back the pads off the rotor though. It sounds like that failed to happen with your calipers. You should be able to push both pistons back. This can be be tricky as you have to put opposing force on both pistons. I have a set of tire levers that work well for this, but y9u may have to search for the right tool. Dirty pistons and seals may be the cause of the pistons not retracting properly. You can try cleaning them and see