What would cause the front brakes to lock up it had pressure in the lines the lever was hard to pull. I opened up a bleeder and released the pressure not much was there it did not squirt out just trickled out. I got it to release and pumped them back up and rode it for a min it seems to be fine now. Any idea what could cause this?

 

Dirty pistons or some blockage in the brake line.

 

Do they make a caliper rebuild kit?