Rear Brake Not Releasing

[Stevo1966]

Just thought I'd ask the question before I purchase any new parts.
My rear brake when pressed doesn't release and return to its resting place, I've tried lubricating the piston and the pivot point, I've bled the brakes and abs pump but still no joy. I'm thinking it's the master cylinder ? Anyone any thoughts or experience of this problem ? Tia

[Versatile1]

Does it fade away or stick.
Fading pedal would be master cylinder, sticking likely your pistons in the caliper.   

[Stevo1966]

Definitely sticking, thanks for the feedback, looks like I'll have to do some spannering the weekend then

[wessie]

any recent work on the bike?

Something as simple as using a pattern brake pad can cause a problem - as mentioned in a recent post on the R1200RS forum. Chap had a binding rear brake and tried everything. The problem went away when he replaced the Ferodo pads with BMW. Presumably there was a tolerance problem causing some sticking.

[Stevo1966]

They were replaced at the beginning of 2021 with brembos so should be no issues there. I'll check the caliper pistons and see if that's where the issue lies 🤞

[Winger]

Just checked mine...have you got slack in the linkage between the lever and cylinder?

[RyanGTXR]

If it's the actual lever staying "down" check the return spring as no matter what you do, it won't come back up if that's gone

[Antares]

Check that the adjustable plunger on the brake pedal is in place correctly, when I was adjusting it I had a this exact scenario too, the plunger we not seated correctly in the master cylinder causing it to constantly be pressed. If you have a diagnostic tool like a Motoscan or GS-911 you can go into the ABS or MOT control modules and see under the "Live data" readouts whether it registers if either brake pedal is depressed or what's going on.
It might be that for whatever reason you just need to adjust your free play now.

[Stevo1966]

Thanks to all for the replies 👍🏼 I'll check things out, unfortunately won't be till the weekend now. I'll let you know how it pans out 🤞

[Stevo1966]

Have now replaced the master cylinder and all seems to be well again 👍🏼