REAR BRAKE

[jason1]

Hi all , know the rear brake has been covered but just fitted new ones to mine this morn. Pistons were a pig to push bck , infact right piston was locked up. So ive soaked cleaned them until moving but still stiffer than should be ( i guess)I fitted the brakes anyway and bled the system till all new fluid. Bck wheel seemed to run free when pushed round. Then took her out for a spin and brake felt good , but when stopped the disc was very hot and stayed hot for min or so . Would this be a sticking brake or just bedding in ? Should say disc is grooved up slighty but doesdnt seem warped or over worn. Any ideas would be great.    Was thinking of taking the caliper off again and soaking pistons longer  :rolleyes

[Fazerider]

It does sound as if a piston is sticking.
Trouble is, if there was the remains of a ring of crud around one it may, depending on how far along the length of the piston it was, have caused some damage to the seals. Best bet is to pop them out and clean the pistons thoroughly, changing the seals at the same time would be wise. Use OEM ones.
The pistons do have a very good chrome plated surface so hopefully you'll find no rust pits anywhere that matters but, if there are, replace them too or they'll wreck the seals.

[jason1]

Many thanks , will give one last clean up tom morn . If no joy new seals , are they easy to replace?

[Fazerider]

It's a somewhat fiddly job getting the old seals out, the dust seals are easy as they're near the edge and are thin... the inner seal is thicker and less flexible. I made up a tool from one of those big staples you find holding cardboard boxes together. To avoid scuffing the front surface of the groove that the seal sits in (which is what the seal presses against when the brake fluid is at high pressure) it's best to hook the seal out from behind. Diagram probably explains it better:





Other than that, and the usual worry of keeping the insides as clean as possible when the outside parts seem to have limitless quantities of grime and loose corrosion trying to get in there, and the hassle of bleeding the last reluctant air bubbles out once you've refitted it... yes, it's an easy job.  :lol
Hope tomorrow's attempt to clean the pistons is a success!

[bootz76]

a common overlooked item,the calipers themselves build up crud and crystals BEHIND the seals in the grooves thus pushing the seals tighter round the piston,scrape the grooves clean.

[jason1]

Many thanks for the info  This mornings adventure was a bit mixed, seemed to have released both pistons until on the final clean the right side got stuck out. Could of been me pumping them out too far.Anyway had to take caliper off and take apart to line up piston correctly to go bck in.Put bck together and with lots of bleeding pistons seem to be working correctly, but pressure still seems low when using brakes on a test ride. Only plus not binding and disc is hot over heating. Think my next step is wait and see how things ride out this week and prob re-bleed the brakes if needed, just hoping the right side piston isnt sticking still, all looks like ok when working tho . Time will tell  :b

[His Dudeness]

you'd probably be better off just replacing the seals. its no biggy. go for genuine seals if you're replacing them

[bikemad62]

I Changed my seals about 3 months ago. When buying my new seals a mechanic came into the spares shop and told me to get red rubber grease, put it on the seal and smear some in the slot the grease keeps the fliud out of the gaps and stops it crystalising. The pistons slid in really easy too. The grease does not affect the brake fluid so it pressures up fine.