[60chevyjim]

if you never changed the rear rubber hose , now is the time to do it.
it sounds like it went bad on the inside and clogged up.
you can check by loosening the metal line that comes from the front of the truck to the rear rubber hose . loosen it up where it goes into the rubber hose at the chassis.

whenever I buy stuff this old or older like I allways do .
I allways start by replacing all the rubber hoses and all the wheel cylinders and the master cylinder .
with the old cars that I build I replace all the metal lines to because
I buy 50's and 60's cars n trucks that have sat unused for a lot of years .

so with your brakes , its better to be safe .
than not knowing if they are going to fail when you need them the most .

this is my friends 65 chassis I that am rebuilding for his 65 truck .