Hey guys. I am having a brake problem. My rod sat for a little while but had this problem since I bought it. The front brakes will hold even after I release the brake pedal. If I do a normal stop they only hold for about 3-5 seconds. If I do a harder stop the front brakes may stay on for 30 seconds or more depending on how hard I push the pedal. If I push on the pedal hard they will stay stuck longer.

On my rod I have 4 front calipers. 2 on either side and all 4 calipers are sticking not just one or 2.
Would this be the calipers or the master cylinder? My calipers are a little rusty. I bought a rebuild kit for all of my calipers and new brake lines (flexible) but I am thinking it can't be the hoses or the calipers since all 4 stick.

What do you guys think? Master cylinder? Crud in the lines? Could all 4 flexible lines collapse and keep the brakes on?

Thanks.