Brake issues
 

I have a 1975 C30 with hydraulic brakes that are causing me no end of trouble. I was deployed for over a year before I got back to where the truck was parked, and now whenever you start the truck the front brakes automatically lock up. With the engine off everything works as it should.
I have gone through two new brake booster units, as I thought that was the problem. I figured the old one could have developed a problem over time, and maybe the first new one was defective, but now I am on the second new unit and the odds are higher that I am chasing the wrong fault.
Anyone else ever have this problem or have any ideas what could be causing it?
Thanks

Re: Brake issues
 

my first guess would be the brake booster too but if youve changed that out how about the vacuum to it is that correct? also is this an instantaneous lock up or is it after you step on the brakes once or twice?

Re: Brake issues
 

As near as I can tell, its instantaneous. Without touching the pedal the brakes lock up. Just the front brakes though. Thanks for your help.