Hey everyone

Have any one experienced that you rear master cylinder is stuck. I tried to open the cylinder and cleaned every part then reinstalled it, but still get stuck when I give it hard push in. 

I will like to order a new master cylinder repair kit , but I’m not sure if that will help my issue. 

Hope you guys can help a new bmw k1100 (93) owner. 

Not having enough free play in the pedal can cause that to happen.

http://www.kbikeparts.com/classickbikes.com/ckb.tech/0.ckb.tech.files/rearbrakeadjust/rearbrakeadjust.htm

Hi,
Thank you for the link. I don’t believe that’s the issue. There is free play. I have detached the cylinder ann pushed it out with a compressor, and when I push it with hand power it get stuck again after a full push it to the bottom.

The cylinder inside is all cleaned and air cleaned, and looks not damaged. I’m wondering if this issue course the pump inside and need to be replaced?

Does it get stuck when you have it disconnected, on the bench, and with no fluid in it except a little bit for lubrication?

Do you have the spring in place under the piston? One of the K  Kronies had problems with his front master cylinder due to an error when assembling. The manual showed the spring in front of the piston instead of behind.
Regards Martin.

Suzi Q wrote:Does it get stuck when you have it disconnected, on the bench, and with no fluid in it except a little bit for lubrication?

Because it should not stick when installed with a fully bled system with no air in the lines or caliper and the pedal properly adjusted.  

On the bench there's nothing giving it resistance.

Suzi Q wrote:Does it get stuck when you have it disconnected, on the bench, and with no fluid in it except a little bit for lubrication?

Yes it get stuck as well. 
I have an other master cylinder which is working but the thread is broken, this does not get stuck. And I can’t use the kit since it’s a 13 mm an mine is 12mm cylinder

Well in that case it can only be either a damaged bore or piston, or a seal swollen because of contact with an unsuitable cleaning fluid for example. 

Edit: did some of these master cylinders have a M4 cap screw in the side for some strange reason, that could jam the piston if it protruded too far into the bore - or am I thinking of something else?

Edit (again): Yes they did, I'm not dreaming! I've just checked the Madass which has an OE master cylinder. I remember an issue with the M4 cap screw in the side of the cylinder body. Have you got such a screw, and could that be the cause?

duck wrote:

Suzi Q wrote:Does it get stuck when you have it disconnected, on the bench, and with no fluid in it except a little bit for lubrication?

Because it should not stick when installed with a fully bled system with no air in the lines or caliper and the pedal properly adjusted.  

On the bench there's nothing giving it resistance.

You are right, I’m trying to not push it all in while bleeding the system -but it’s difficult.. 

If I get it bleed out it will work probably. Is it sustainable to have a cylinder that may get stuck again..

I'm confused now. 
Duck's point is that, if the brake pedal is so badly adjusted that it does not allow the cylinder piston to fully retract when released, then the port from the reservoir may not be uncovered, which means that the system becomes starved of fluid leading to the cylinder piston not fully retracting.
But you've said that the problem is still there when the cylinder is disconnected and on the bench?

Jakobm3ro wrote:If I get it bleed out it will work probably. Is it sustainable to have a cylinder that may get stuck again..

Is what sustainable—your life? I would not place bets on that if your motorcycle's brakes are unreliable.

Suzi Q wrote:I'm confused now. 
Duck's point is that, if the brake pedal is so badly adjusted that it does not allow the cylinder piston to fully retract when released, then the port from the reservoir may not be uncovered, which means that the system becomes starved of fluid leading to the cylinder piston not fully retracting.
But you've said that the problem is still there when the cylinder is disconnected and on the bench?

Correct, and now after fighting with the piston to get it out of the cylinder, it get stuck immediately when I try to push it in. I believe that’s it, I have to get a new one. It’s risky business..