after replacing a rear wheel brake cylinder (right rear) on my 1989 d21 hardbody (4cyl;auto;rwd), i tried bleeding my brakes several times but the pedal still goes to the floor initially. the pedal gets fairly firm after one pump, and will stay firm as long as it's pressed down but after the pedal comes back up, it goes back to the floor again when pressed. the engine also sputters and shakes when i apply the brake, and usually dies, but the idle is fairly low and the trucks been sitting for several months with only periodic starts. i'm considering the master cylinder now, and would welcome any thoughts. only about 85,000 miles on it so far.