I recently changed the brake fluid in my 450 EXC, twice now during moderate off road riding the rear brake starts to drag and heat up. When I notice and pull the clutch in to stop the rear brake slides the rear wheel to a stop with the rear brake smoking hot. Both times I backed off the pedal stop to let the brake pedal up and cured the problem on the trail. I don't think I drag the rear brake, and the reservoir does not look to be overfilled. Any Ideas? Thanks..
I had a similar thing happen on my 640. Tweaked the pedal stop and fixed it (mine was also missing the pedal return spring) . Maybe the pistons in the caliper are gunked up and causing the pads to drag. Clean and grease the caliper slides and pistons (very light grease) for a start.
The dust seal can get squashed between the cylinder and piston and not let piston return. Happened on my DR 650 front brake.
I will look at those areas today, when I stopped the pedal was rock solid with line pressure, when I back off the pedal stop a quarter turn, pressure released and the pedal gets all the original free play back and works fine for the rest of the day. I know this is not doing my rotor any favors....
No grease/oil/gas on brakes, use brake fluid only for cleaning or a brake-kleen spray type product. Keep brake fluid off paint and plastics. No dino oil products around brakes brothers. http://en.wikipedia.org/wiki/Brake_fluid Bleed the system, check the linkage. Dot 4 only! bill
don't over think the prob....ur dragging the rear brake...lower the pedal below the level of the foot peg....even to a point of having to "search for it",,,that will prove it :)....i at any one time have at least 5 ktm' s of my own in my garage... and most have race numbers below the number of 3 best of luck dave
You didn't mention if it's a newer bike or an older one... There should be a return port or compensation port in the master cylinder, it's a tiny hole. If it gets clogged, the fluid can't return from the caliper to the master cylinder, the brake will do exactly as you are saying, it will just come on and drag. This makes heat, so the fluid expands and the brake comes on harder, which makes more heat. Eventually it just locks up. Very common on old bikes that have not had the brake fluid changed regularly.
Is that port visible inside the master ? I will check it , and already lowered the pedal. Thanks for the input.
To be truthful I haven't looked inside a KTM master cylinder, so I don't know. On other systems this port is less than a mm in diameter, so it is easy to clog with loose rust particles in there.
All of these things are possible. But, since it doesn't happen until it gets hot from use, very likely that the reservoir is too full. This is a pretty common problem. When the rear brake is cold, reduce the fluid level to the lower mark. You might want to go ahead and change out the fluid too. Does the wheel start to roll again after sitting a few minutes? If so, it is probably hydraulic lock up from fluid expansion.
Have you adjusted the rod that goes into the rear master cylinder? If it doesn't have enough "slack", it won't let the brake fluid back into the master cylinder quick enough after releasing the brake. In effect, it is dragging the brake for you, the fluid gets hot, expands and it'll eventually lock the rear brake.
Does that use the same (crappy) Brembo rear MC as the F650s? If so, pull it and check if the white nylon cylinder guide sleeve is stuck due to corrosion in the housing. Stupidest MC design I have seen in a while.
Checked the areas that were discussed, bled it again, normal pedal freeplay and feel. After sitting overnight the pedal has almost no resistance and will barely pump up with about ten cycles. I made no adjustments to the pushrod or pedal stop, no fluid anywhere and normal level in reservoir. I must be getting air in when I bleed it...???
I am having a similar issue with my 2015 350 XCF-W. During a day of technical riding, my rear brake would bind up. I would crack the bleeder screw, release the pressure and continue for a while, repeat. Got home, cleaned up the caliper, and had 4 straight days of riding with no issues. The last time I went riding, the problem returned. I have the back wheel off, and with the bike cold, I'm unable to push the brake piston back into the caliper with a C clamp, even with the reservoir cap off! If I crack the bleeder or loosen the bolt holding the line to the top of the master cylinder, the pressure is released. tkent02 mentioned a return/compensation port. Does anyone know where it is? Also, what is the small, dark, torx head bolt right under the site glass of the master cylinder?
Make sure all the pressure on the master cyl piston has been released. If the pedal is keeping the piston slightly depressed, the fluid can not get back to the master. The hole you are looking for will be at the bottom of the master cyl. I doubt it is clogged, a c-clamp would have pushed past any clog.
