Back brake sticking. Help!

[ScottT]

Same thing happened on my F650ST, i went through everything on the caliper and no joy.
Master cylinder was sticking a repair kit sorted it out after 2 attempts i put the seal in the wrong way round the first time, the instructions are a bit vague.

[steve the grease]

If the back brake is sticking on there can only be 2 reasons, either the piston is sticking in the caliper , or there is residual pressure in the system pressing the piston onto the pads.
First test , undo the bleed nipple if the wheel now turns then the problem is residual pressure , the problem is in the master cyclinder, or very rarely a collapsed rubber hydraulic pipe.
if its still sticking then the problem is in the caliper, the only thing that retracts the piston is the square rubber seal in the caliper, it deforms as the pressure builds up and as the pressure is released it returns to its original shape , pulling the piston a few 'thou' back so as to removepressure from the pads. Very often there is corrosion on the narrow ring between the outer seal and the inner seal , this siezes the piston in place.

[HAMMERHEAD]

If the back brake is sticking on there can only be 2 reasons, either the piston is sticking in the caliper , or there is residual pressure in the system pressing the piston onto the pads.
First test , undo the bleed nipple if the wheel now turns then the problem is residual pressure , the problem is in the master cyclinder, or very rarely a collapsed rubber hydraulic pipe.
if its still sticking then the problem is in the caliper, the only thing that retracts the piston is the square rubber seal in the caliper, it deforms as the pressure builds up and as the pressure is released it returns to its original shape , pulling the piston a few 'thou' back so as to removepressure from the pads. Very often there is corrosion on the narrow ring between the outer seal and the inner seal , this siezes the piston in place.

Nice little bit of insight there. Thnx for sharing. (thumbs)

[dubber68]

Cheers Steve that will help both now and no doubt in the future.

[dubber68]

Well found some time today to work on the brakes. After changing the seals and bleeding again everything seemed fine until the test ride and then it started binding again. It turned out to be the master cylinder and after changing that everything was fine and a small ride out was enjoyed.

Thanks to all for their advice.

[dubber68]

This is the second rear master cylinder in 42k miles. They seem to go at 20k on this bike, not sure why.

[zimtim]

Had same on my BMW F650gs, I found that the KTM 640 master cylinder was the same but a damn sight cheaper :whistle:

[hotbulb]

Glad to hear it's fixed, and I hope you enjoyed the "test drive" .

Sent from my XT1039 using Tapatalk

[rodyorkabr]

If the back brake is sticking on there can only be 2 reasons, either the piston is sticking in the caliper , or there is residual pressure in the system pressing the piston onto the pads.
First test , undo the bleed nipple if the wheel now turns then the problem is residual pressure , the problem is in the master cyclinder, or very rarely a collapsed rubber hydraulic pipe.
if its still sticking then the problem is in the caliper, the only thing that retracts the piston is the square rubber seal in the caliper, it deforms as the pressure builds up and as the pressure is released it returns to its original shape , pulling the piston a few 'thou' back so as to removepressure from the pads. Very often there is corrosion on the narrow ring between the outer seal and the inner seal , this siezes the piston in place.

Steve you should post more often!..fantastic advice..thank you

[rlkat]

A problem I had, when I replaced the last set of pads on my Transalp, was that the tabs on the brake pads were too tight in the slots in the caliper. The tolerances were too tight so I had to file the tabs down slightly so they could move freely. Same thing happened when I changed my brake pads on my Honda car.