BD 264 vacuum pressure

That stored vacuum must slowly leak out when the truck sits, I can't think of any old truck I've driven with power brakes that you didn't feel the brake pedal rise when you started it up.

That really isn't the point, it is what is available to help stop the truck when it is driven that counts. Air brake trucks don't have any air pressure when started after sitting either.

I won't say my last post was off topic but it was pretty close to falling off the edge. Just something I have noticed.