95 F250 5.8L stick. Front left brake locked front right dragging. Removed FL caliper and tried to push piston back. Wouldn't move. I pulled the pistons and they're fine, no gouging, marring, corrosion or rust. They were full of fluid. I emptied the fluid put pistons back in. They went in easy. Stepped on brake and it filled again and locked. I'm wondering if it's a bad rubber line. Any suggestions to narrow it down?
Thanks.

 

Sounds like rubber hose is collapsing inside.

 

X2 on the rubber flex line, it is strange how this happens but it acts just like a 1 way valve. I have seen the same thing happen to a garden water hose too.

 

Thanks for the replies. I ordered a hose it'll be in tomorrow. Guess I should probably get the right side also.

 

Almost def the rubber line..I've been thru this and it's an easy & effective fix. FYI, you should replace both sides as it'll happen to the other one as soon as you've replaced the bad one!

 

Yeah I already called the parts store and ordered the other side.

 

easy way to see if it is the rubber hose is apply brakes. then crack loose the bleeder. if fluid shoots out under pressure and the wheel spins again, caliper is good and the rubber hose is collapsed internally, or the master cylinder piston is not returning to center holding the brakes engaged.

 

That's how I got the caliper to unlock, but I didn't open the bleeder, I opened the bolt on the hose block.