My brakes are really getting bad, last year before i put it away i changed the rear brakes, drums and everything, also replaced the front brakes. bled the brakes and that work a little, but now it has a lot of air in the brakes. I mash on the brakes and i hear a lot but air. If i sit in gravel with my foot on the brake, it starts to peel out. It feels like im trying to stop a 10,000 lb car when i slam the brakes on. Am i missing anything? do you guys think its the master cylinder? Its looking pretty old and rusty, what else COULD it be??