Ford Repair: brakes, f 250, brake booster

Question
i just replaced my master cylnder on a 93 f-250 and as you drive about a mile or two the front brakes will start to engage and not come off unless you let the truck sit for a while.i have bled the lines. what could it be

Answer
Hello and thanks for the question...I'll try to help.
When replacing the master cylinder --did you fool around with the rod in the brake booster at all? If you did.you're going to have to reset it. If not, I would suggest that you get a different master cylinder and rebleed the system.
Hope this helps,
Erik