Hi

My lads 2011 125 evo rear brake is locking on after a hard work out. leave it to cool and its fine. So after 30ish minuets rear wheel hopping and hard practice I am guessing the fluid is so hot it lockes the brake on. It has happened at 1 trial when he rode a lot of sections after each other trying to make up time. This is a new thing to happen, so something is not right. New seals in master cylinder????. Can anyone shed some light on this or had the same problem.

Pete

Read your post and you almost have the fix. Something is too tight or he is riding the pedal. Chances are the rod is adjusted too tight. Have seen the same things happen at long distance events or long steep trails whre you are constantly on the rear brake for 20 minutes plus.

This happens with many types of back brake, but is usually due to a combination of 2 things.

The brake pads wear tapered due to the ingress of mud/grit and because of pad wear, the adjuster is screwed out more to regain the operating position. Adjustment causes the rear brake master cylinder piston to go higher up the cylinder and may even cover the inlet/return port from the reservoir - even when in the non-braking position.

Then when using or dragging the brake, the pads/pistons/oil gets hotter and expands, but because the port to the reservoir is closed, the pressure builds up and applies more brake. That's why cooling releases the brake.

This can damage the seals in the caliper.

The fix - check brake pads regularly for taper as under pressure the pistons may cant in their bores and can jam, if tapered more than 0.3mm - file flat again. This gives longer pad life and better braking.

After adjustment of rod length, always check that the pads fully release off the disc.

Gday, after making sure there is free travel in the pushrod, also make sure that the reservior is not full to the top when cold - so there is some room for the expanded fluid to go!

Cheers,

Stork

Hi

My lads 2011 125 evo rear brake is locking on after a hard work out. leave it to cool and its fine. So after 30ish minuets rear wheel hopping and hard practice I am guessing the fluid is so hot it lockes the brake on. It has happened at 1 trial when he rode a lot of sections after each other trying to make up time. This is a new thing to happen, so something is not right. New seals in master cylinder????. Can anyone shed some light on this or had the same problem.

Pete

my '10 evo does the same thing. starts dragging and then heats up quickly... I need to look at the fluid level too i guess.