86yamahaxt

He I hope you guys can help me I'm new to working on bikes and have this problem I can't figure out. Last weekend I rebuild my front brake caliper. I bought the bike a few months back and after riding for about 20-30 min the brake would lock up. I found there was a'lot of rust in the system so I flushed it out and installed all new seals and purged the lines of air. I was out riding it today and it started locking up again. I hope somebody out here with one of these bikes may have an idea on what to do with it.