The master cylinder on my truck was new when I bought it . I bled the brakes and the pedal is still spongy. No air in the lines , no leaks & the wheel cylinders & lines are new. Could it be a 1/2 ton master? The only marking I see on it is the number 1. Does that mean 1 " bore? I measured the outside diameter of the housing & it is 1 5/8",if that helps. SEE YA! Mark
