O.K driving truck
(91 f 250 4x4 7.3 ext xlt) com ing to a red light apply brakes first stroke normal all others hard like a rock?Then light goes green drive a little while red light and again first stroke normal and the all others hard like a rock it's very hard to stop these machines when the pedal is like rock.
If the vacum pump was bad it would be hard all the time right?
Or is it the pressure relief valve in the booster gone that is why first good and rest are bad?
It's driving me batty please help.

 

O.K. first of all I do not not know of a pressure relief valve in a brake booster. I do beleive that your are having a booster issue. i am to assume that your engine is a diesel since you mentioned that it had a vaccum pump. Heres what I would do. start you engine and let it run for approx. 15 seconds. wait 30 seconds and take the line that goes into the booster and pull out on it gently. If you hear air rushing in than more than likely the booster itself is o.k. If it passes that test,than put a vaccum guage on the system and see how much vaccum the pump is making. approx 18'' of HG at idle is o.k. then shut the system down and watch the guage. look for a leak. good luck.

 

I had the same problem with my truck the first push of the pedal was good then hard as a rock and hard to stop ended up being the vac pump it was barely working

 

I suspect the vacuum pump is slowly building up enough vacuum for a single brake aplication, but is unable to keep up with normal braking patterns in average driving. You can easily test it by pulling the boster hose and checking for how quickly the vacuum builds up when placed against the palm of your hand (getting very technical here lol).