runninn Posted February 21, 2015 Share Posted February 21, 2015 (edited) Sorry to start a new thread...but I have this thing apart in the rec room & know someone has a logical answer. (Wife is gonna kill me if I don't get it moved....) Brakes still sticking...determined it's the outer (2) pistons as I see the inner retract while watching the actuation. Changed to hi-temp Motul 600, cleaned pins, greased secondary MC, etc. The kicker is that I open the BACK rear bleed valve and the pads retract properly. Something is obviously restricting the flow & opening the bleed valve relieves the pressure. If the MC return (rear ...under the bodywork) is gunked up, how can it be cleaned? (Fluid was changed) Other ideas where it would work OK by opening the rear bleed valve? thanks! Edited February 21, 2015 by runninn Quote Link to comment Share on other sites More sharing options...
TuffguyF4i Posted February 21, 2015 Share Posted February 21, 2015 You're wasting money on high temp brake fliud. Did you vacuum bleed the system yet. Quote Link to comment Share on other sites More sharing options...
runninn Posted February 21, 2015 Author Share Posted February 21, 2015 Used Mityvac to vacuum bleed...possible air pocket? Quote Link to comment Share on other sites More sharing options...
TuffguyF4i Posted February 21, 2015 Share Posted February 21, 2015 That's the right way to do it. Does the rear brake foot lever feel squishy at all? You could always remove the suspect line and blow it out with brake cleaner. Quote Link to comment Share on other sites More sharing options...
blackhawkxx Posted February 21, 2015 Share Posted February 21, 2015 My thought is that it is one of the master cylinders. Study the manual. I have never had that problem on anything but I am sure that some on here will chime in. Quote Link to comment Share on other sites More sharing options...
Redbird Posted February 22, 2015 Share Posted February 22, 2015 Can't recall which is which, but the outer two pistons and the center piston are controlled separately by rear brake pedal and the secondary cylinder on the front fork. Going entirely from very faded memory- I think the outer two are activated by the secondary on the fork, in which case you're going to need to check the proportioning valve that you'll find on the right side of the bike under the rear cowl and the return circuit on the cylinder itself. If I'm wrong, and that's not only possible but likely, then troubleshooting will be easier, as the problem will be somewhere between the rear pedal the the caliper. It could also be the piston seals sticking, but that would be too simple. Quote Link to comment Share on other sites More sharing options...
tomek Posted February 22, 2015 Share Posted February 22, 2015 Bleeding does not hurt but it certainly won`t fix dragging brakes. Two outer pistons are activated by secondary master cylinder on the left fork/brake caliper. Bottom part of caliper is attached to the fork via pivot point, upper to the pushrod of the master cylinder. So basically when you hit the front brake ( or rear too ) the caliper pushes on secondary master cylinder. Make sure the secondary master is not sized and top of left caliper swings freely. Also when you do that have someone check out whether two outside pistons in the rear caliper move. Quote Link to comment Share on other sites More sharing options...
runninn Posted February 22, 2015 Author Share Posted February 22, 2015 Today's update. After actuating the mechanical Secondary MC (front wheel) it appears only the front piston is working in the rear caliper (both outers are supposed to work). Some gunk does appear on the pistons so its caliper rebuild time. I have already pulled the caliper & am in the process of pulling the pistons to clean them as necessary. Suggestions on a caliper rebuild? I am planning to use brake fluid & really fine sandpaper (jewelers type) to clean the pistons. Is seal replacement recommended? thanks Quote Link to comment Share on other sites More sharing options...
tomek Posted February 22, 2015 Share Posted February 22, 2015 Ideally - yes, but you might get away without seal replacement. You would have to order it, then wait 2-4 days for parts before finishing the job. It all depends on your time frame. Something like 800 or finer sandpaper will do. Quote Link to comment Share on other sites More sharing options...
jon haney Posted February 24, 2015 Share Posted February 24, 2015 The only reason I can see to sand on the pistons is if you have corrosion on them. If that is the case, get new seals. The pistons are zinc plated, so if you sand on them, removing the plating, you make corrosion more likely in the future. Also, if re-building the caliper doesn't fix the problem, just De-link the system. Much easier. Quote Link to comment Share on other sites More sharing options...
runner Posted February 24, 2015 Share Posted February 24, 2015 My thoughts exactly. If the caliper rebuild falls short it's de-link time! Quote Link to comment Share on other sites More sharing options...
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