well i was driving the 68 when the brake peddle went soft. Before this happened i would put pump the brake once and them hld it down and it would stop. What would cause this?

 

Systems is leaking fluid or no one has checked it for a long time..
You shouldn't have been drivring it that way.

 

It's past time to replace your master cylinder.

 

Just bleed your breaks,on these old trucks breaks go from solid to squishy in a day. Last time this happened on my 67, A lot of black crap came out when i bleed them, I also adjusted the breaks*(drum Breaks) and it was as good as new.

 

Get a new master cylinder, bench bleed it (before installing, fill it with fluid and pump it until only fluid comes out--it helps if you get a quality master cylinder with plastic fittings and tubes that allow you to direct the fluid right back into the cylinder), install it, then bleed the system out really well. This is also a good time to pull your drums and check for leaking wheel cylinders. Gently peel back the rubber caps on the wheel cylinders. If it's wet inside at all, replace BOTH cylinders on that axle.

Oh, and make sure that the drums are ON the vehicle when you bleed the brakes. Apparently I wasn't explicit enough in my instructions with one of my friends on that one...