2012 rear brake problems

[Dsoltis]

My rear brake on my rt works sometimes and sometimes it goes all the way down but will pump up. Very random when this happens.  I’ve cleaned the pins and slides and bled them. I did not get any air out of them. There was no work done on the brake system that may have started this problem. Any ideas or help would be much appreciated

[dirtrider]

45 minutes ago, Dsoltis said:

My rear brake on my rt works sometimes and sometimes it goes all the way down but will pump up. Very random when this happens.  I’ve cleaned the pins and slides and bled them. I did not get any air out of them. There was no work done on the brake system that may have started this problem. Any ideas or help would be much appreciated

Morning   Dsoltis

 

Does the rear wheel have any lateral play (put bike on center stand, then grab top & bottom of rear wheel & see if you can move or wobble it. (if you have excess wheel play it's possible for that play to kick the brake pads back into the caliper).

 

If the above is OK then the usual cause is a defective rear brake master cylinder (the internal piston cups aren't sealing very good so at first brake apply the brake fluid just by-passes the piston & cups).  Then after a few strokes the piston cups expand against the bore & start to seal again.   

[Dsoltis]

I will check the rear wheel play when I get home in a while.  If the  master cylinder was bypassing wouldn’t it do it every time I applied the rear brake.  It is very random. Thanks 

[Dsoltis]

Dirt rider.   I checked for play in the rear wheel and there is a very minimal amount but if the tolerance is zero then yes I have some play in it. I just put new tires on and changed the final drive fluid and it looked like new about 500 miles ago. Thanks 

[dirtrider]

1 hour ago, Dsoltis said:

Dirt rider.   I checked for play in the rear wheel and there is a very minimal amount but if the tolerance is zero then yes I have some play in it. I just put new tires on and changed the final drive fluid and it looked like new about 500 miles ago. Thanks 

Afternoon Dsoltis

 

A little wheel movement (under 1mm cold) is pretty normal. Doesn't sound like you have enough wheel deflection to kick the brake pads back.  

[dirtrider]

1 hour ago, Dsoltis said:

Dirt rider.   I checked for play in the rear wheel and there is a very minimal amount but if the tolerance is zero then yes I have some play in it. I just put new tires on and changed the final drive fluid and it looked like new about 500 miles ago. Thanks 

Afternoon Dsoltis

 

Not necessarily, they can act kind of random at times. It can also depend on how FAST you apply the rear pedal. If you are getting fluid by-pass then usually slow pedal apply will make it worse & a very fast full apply usually seats the piston cups.    

[Dsoltis]

Dirt rider.   I agree with you that the master cylinder is most likely the problem.  I’ve been looking for a rebuild kit but can’t find anything. I have found some master cylinders but would rather rebuild the one I got. Do you know of any kits?  Thank you for taking the time to help me out 

[dirtrider]

21 minutes ago, Dsoltis said:

Dirt rider.   I agree with you that the master cylinder is most likely the problem.  I’ve been looking for a rebuild kit but can’t find anything. I have found some master cylinders but would rather rebuild the one I got. Do you know of any kits?  Thank you for taking the time to help me out 

Afternoon Dsoltis

 

No, I don't know of any kit but you might try Beemer Boneyard, if there is a (decent) one available they probably have access to it.

 

Problem with re-building yours is you don't know exactly what is wrong with yours, if just bad piston seals, or leaking piston seals then a rebuild will probably make it work. On the other hand if you cylinder bore is oversized or the actual piston has an issue then most rebuild kits won't repair this. 

 

You might try calling your dealer & give them your VIN number (or check online for recall info), while I haven't heard of one there might possibly be a BMW service recall (or something similar) on your rear master cylinder. In the past BMW has had a few runs of improperly functioning rear master cylinders & sort of did a service bulletin/ internal recall to replace that small run of master cylinders. 

 

I have heard  of (very similar) rear brake complaints on the later 1200 GS (wethead bikes) --- Check your messages as I sent you a link to those.    

[Dsoltis]

Dirt rider. I will call my dealer tomorrow and check on the possible recall which reminds me that I never followed up on the last recall. I will check with beemer boneyard for a kit or new cylinder. Once again thanks and it might take a while but I will post the results 

[Dsoltis]

Wanted to give an update on my brake problem.  A friend and I bled the rear brake several times and still didn’t get any air but in the process we were able to get the brake to fail repeatedly in the garage which is something I couldn’t get it to do. I ordered a new master cylinder and after a couple hundred miles it’s still working fine. Thanks for the advice much appreciated. 

[dirtrider]

15 hours ago, Dsoltis said:

Wanted to give an update on my brake problem.  A friend and I bled the rear brake several times and still didn’t get any air but in the process we were able to get the brake to fail repeatedly in the garage which is something I couldn’t get it to do. I ordered a new master cylinder and after a couple hundred miles it’s still working fine. Thanks for the advice much appreciated. 

Morning Dsoltis

 

Glad you have it sorted, please give us another update to this thread in a couple of thousand miles if you get a chance.