I have an 80 F250 4x4 thats my project truck. it has a 351M and a C-4 tranny. it idles really rough when in drive, and just a little rough when in park. ive got the carb adjusted as good as it will get and i cant find any vacuum leaks (yet) any advice? but my bigger problem right now is the brakes. theyre power brakes but have been having issues. originally when i got it they would suck down about halfway really quick and after that were basically just manual brakes. now they suck down really fast just by barely touching the pedal. and they stay stuck down! they wont return without me prying them up with my foot. I was thinkin probably a bad brake booster? looking for other input before i go out spendin money and rippin stuff apart...

thanks!

 

Rough idle and bad brakes makes me lean toward a bad vacuum between the intake and booster. If there are no obvious leaks (use some carb cleaner and shoot it around the intake) then it may well be the booster. I think you were right on your guess... sounds like a booster problem.