Deore pistons not retracting

mac_man

Have a pair of Deore disc brakes and one of the pistons is not retracting fully. The lever does not spring back properly when released and the pads are still gripping the rotor. If I push the lever out the pads unstick themselves from the disc, but there is still rub on the disc. If I prise the pads/pistons apart when off the bike, with a flat blade, and refit them, the rubbing disappears till the next application of the brakes.

Too much fluid in the system?

cooldad

Did you add any?

The Rookie

If the lever isn't springing back it sounds like a sticky lever issue.

mac_man

[url=http://www.bikeradar.com/forums/viewtopic.php?p=19748745#p19748745]cooldad[/url] wrote:

Did you add any?

Not me. Got them 2nd hand in what appeared to be excellent condition. But no idea if they've been re-bled since new.

mac_man

[url=http://www.bikeradar.com/forums/viewtopic.php?p=19748770#p19748770]The Rookie[/url] wrote:

If the lever isn't springing back it sounds like a sticky lever issue.

Sticky lever issue?

The Rookie

It moves on a pivot pin, any censored in there will stop it moving freely, so clean it all up nicely!

Rightarmbad

Probably a bent or sticky lever as suggested above, but I have seen this happen when people put DOT fluid in shimano and the seals swell.
Take out the lever fill screw and check the colour of the fluid.

It may not just be a single pivot either, depending on the year model it may or may not have servo wave and if so there is an extra pivot and a sliding bit as well.

mac_man

Thanks for the replies folks. Found the cause of the sticky lever... it was catching on the shifter body underneath, so just moving them apart slightly cured that problem. Thanks for the useful tips about keeping the levers clean. Anyhowo... I've been persisting with aligning the pads and the rubs is barely noticeable now, but still there, and the amount of effort to get them aligned seems excessive. Normally to align brakes I've just kept the bolts loose, pull the brake, tighten the bolts and alignment is sorted. I've noticed a really miniscule wobble in the rear disc and can see it catching on the pads but I would have a expected a little more tolerance TBH. The pads seem a bit too close in the open position. I have the same brakes on another bike, so will compare pad position on each and maybe swap them over to see if there's a difference. Maybe it is the discs...

The Rookie

The pads should lightly rub the disc, the disc is what pushes them back, if the disc is warped then straighten it!

If the pads are worn off square then aligning the calliper by pulling on the brake will misalign the calliper, sometimes it's better to do by eye.

Rightarmbad

[url=http://www.bikeradar.com/forums/viewtopic.php?p=19750375#p19750375]The Rookie[/url] wrote:

The pads should lightly rub the disc, the disc is what pushes them back, if the disc is warped then straighten it!

If the pads are worn off square then aligning the calliper by pulling on the brake will misalign the calliper, sometimes it's better to do by eye.

The disc does not push the pads back, the square edge seals pull them back. They also perform the auto adjust function.
Shimano brakes on a good disc should not rub at all.

Herdwick

Disc rub also can be caused by the ''lazy piston'', one of the two pistons moves less when retracting so no matter how much you allign the caliper by loosening the bolts and grabbing the brakes won't center caliper on the disc, and one side is closer to the disc than the opposite. A way to fix this is to push the disc by hand on to the lazy/sticky piston to make some room to compensate.


Once in a while I remove the pads and force the caliper pistons out just enough not to drop off of the caliper, one at a time, clean them with alcohol and then put some light grease with an ear bud and push it back in. this keeps the seals soft and less sticky