mooregas Posted May 14, 2010 Report Share Posted May 14, 2010 the rear brake on my 09 pro works fine when you press it , but when you apply continual pressure it looses the peddle, ive replaced the seals in the caliper and there dosent seem to be fluid leaking from anywhere, i eventualy managed to bleed it and get a good peddle but after a few pumps the problem returns and i get a little air at the bleed nipple as if air is been drawn into the system, ive bled the system so many times that the air must be out as it couldent of worked with the amount of air thats came out. any ideas? Quote Link to comment Share on other sites More sharing options...
greg Posted May 14, 2010 Report Share Posted May 14, 2010 I over tightenened the nuts on the master cylinder? deformed the olive ,hard to find , hope it helps. Quote Link to comment Share on other sites More sharing options...
ggjord Posted May 14, 2010 Report Share Posted May 14, 2010 (edited) replace the pump piston and seal kit 150.00.396c it will be letting by. if your fluid in the pot is dirty this is a good indication as well that its knackered. done mine today with the same symptom as yours. Edited May 14, 2010 by ggjord Quote Link to comment Share on other sites More sharing options...
mooregas Posted May 14, 2010 Author Report Share Posted May 14, 2010 Before i replaced the caliper seals i did notice the fluid in the pot was dirty, but i just assumed the problem was the seals in the caliper. ill try replacing the master cylinder seals now, any tips on bleeding the system? people say to syringe fluid back from the caliper, but ive tryed this and it seems to take more pressure than you can deliver with a syringe. cheers for the help Quote Link to comment Share on other sites More sharing options...
thespikeyone Posted May 14, 2010 Report Share Posted May 14, 2010 when you test it is it stationary on a stand or is the back wheel moving????? could be a bent brake disc Quote Link to comment Share on other sites More sharing options...
jonny042 Posted May 15, 2010 Report Share Posted May 15, 2010 the rear brake on my 09 pro works fine when you press it , but when you apply continual pressure it looses the peddle, ive replaced the seals in the caliper and there dosent seem to be fluid leaking from anywhere, i eventualy managed to bleed it and get a good peddle but after a few pumps the problem returns and i get a little air at the bleed nipple as if air is been drawn into the system, ive bled the system so many times that the air must be out as it couldent of worked with the amount of air thats came out. any ideas? Same symptoms as my '09 pro (that only has 10 or 12 hours on it). When I took the Master Cyl apart the seal was knackered, looked like a peice of something was stuck in the hole that lets fluid in from the resevoir, and it was abrading the seal. I ordered a kit and will install it once the pain goes away. What a co-incidence that it was the REAR brake. Please let us know the results. Quote Link to comment Share on other sites More sharing options...
mooregas Posted May 15, 2010 Author Report Share Posted May 15, 2010 Ive tested it on the stand and riding the same problem in both cases! you can see the peddle gradualy moving down as it losses the pressure, think im going to try a new master cylinder seal kit. cheers anyway Quote Link to comment Share on other sites More sharing options...
mooregas Posted May 15, 2010 Author Report Share Posted May 15, 2010 Problem fixed! master cycinder seal shot. Quote Link to comment Share on other sites More sharing options...
jonny042 Posted May 15, 2010 Report Share Posted May 15, 2010 Problem fixed! master cycinder seal shot. Great to hear - I'm just in from getting mine done too. Syringe bleeding didn't seem to do the trick, I had to "pressure" bleed the system by pumping fluid through with the M/C, but with a screwdriver, not the pedal - not enough travel with the pedal, had to push it right in to rid the system of air trapped in the M/C. Quote Link to comment Share on other sites More sharing options...
jmurray Posted May 16, 2010 Report Share Posted May 16, 2010 I'm on my 3rd rear brake master cylinder 2 new 1 kit, the inner seal gets mushy and starts coming apart I'm using dot 4 brake fluid 2010 280 any ideas !!!!!!!!!!!!!!!!!! Quote Link to comment Share on other sites More sharing options...
jonny042 Posted May 16, 2010 Report Share Posted May 16, 2010 I'm on my 3rd rear brake master cylinder 2 new 1 kit, the inner seal gets mushy and starts coming apart I'm using dot 4 brake fluid 2010 280 any ideas !!!!!!!!!!!!!!!!!! Use dot 5 silicone? But wow that shouldn't be happening..... now I'm worried for mine. Quote Link to comment Share on other sites More sharing options...
jmurray Posted May 16, 2010 Report Share Posted May 16, 2010 I don't think you can use dot 5 because the seals aren't silicone resistant in the rear brake system Quote Link to comment Share on other sites More sharing options...
laser1 Posted May 16, 2010 Report Share Posted May 16, 2010 I used dot 5 on my last bike w/o problems. Im pretty sure its OK, but better check if they changed the seals in 2010 or somthing. Quote Link to comment Share on other sites More sharing options...
jse Posted May 17, 2010 Report Share Posted May 17, 2010 I used dot 5 on my last bike w/o problems. Im pretty sure its OK, but better check if they changed the seals in 2010 or somthing. DOT-5 (Silicone) is essentialy chemically inert and can be used with just about all o-rings and seals. It, however, is slightly compressible so it may give a slightly "spongy" feeling, which in back brakes is generally not a problem as it helps to avoid sudden lockup. If you change to DOT-5 from DOT-3, 4 or 5.1, you will want to completely flush the system as 5 is not compatable with the other fluids (this from experience and advice of my Chemical Engineer buddies). Jon Quote Link to comment Share on other sites More sharing options...
jmurray Posted May 17, 2010 Report Share Posted May 17, 2010 I'm not sure what is causing the seal to come apart I end up with little bits of rubber in the fluid, it came with dot 4 so thats what I have been using Quote Link to comment Share on other sites More sharing options...
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