rear brake locking up

[t300mag]

I will ride for about 15-30 min and my rear brake will start to slowly locking up untill it will not go any more. The brake pedal will not move when it happens , it is like the pressure will not release

 

[motomad]

Sounds like boiling brake fluid.How long's it been since you've changed it?

 

[Durt Cycler]

Change the fluid.

 

[Einstein]

Got a leaded right foot :)

 

[t300mag]

i changed it right after the second time it happened

 

[jmics19067]

did you use the right brake fluid? if you happened to mix dot5 with dot 3 or 4 brake fluid you will get this problem < dont ask me how I know >. If you have an old can of brake fluid lying around your garage it is possible that it absorbed water also.

also check to see if your rotor is bent and / or your caliper sticking. worn/rusted brake pins?

Did you happen to be jumping and possibly land with your foot on the brake pedal recently maybe the little rod that goes into the master cylinder is bent or adjusted too tight. Is the brake return spring on the pedal?
time too scrutinize each and every part individually and also how each part works in the assembly . If anything is questionable or you are unsure of it toss it and get new, brakes are definately one area you don't wanna play cheapskate with

 

[NO HAND]

You still got too much humidity or air trapped in your brake line. This is about the only thing that could expand and lock up the brakes. You need to get fresh brake fluid. Sometime what was left in the can from last year is wasted because it caught some humidity. Get some new Dot 4 fluid in and when you are finished replacing the fluid, back bleed it by using a flat blade screwdriver and separate the pads. This will ensure you remove the few bubbles left in the brake line.