braking problem

[metropolis909]

sooo this has gone on for about 3 months and welll its at the point where its dangerous... my truck driving down the road brakes perfect... until u build up some good rpms where if u panic stop my pedal is rock hard till the rpms come down... and i notice when i park it i leave my foot on the brake and shut it off and the pedal pushes back and truck will roll forward till its on park pin.... now this all happened shortly after i seafoamed my truck... thru the vaccum line... now the truck runs perfect (im also mechanic soo its always up kept) i dont see any vacum leaks and where its fine driving around i dont see how it is a leak it would do it all the time soo my next option is im think its either my booster or the check valave going into booster... now can i apply vaccum to my booster with a vaccum pump to see if thats my issue if so how much psi should i do it at? i really need to fix this b4 i hit sum1... any help is appreciated...

 

[westtnfx4]

Your master cylinder or booster should be checked....also weak brake lines are common on those trucks....the rubber part. It's a process of elimination.

 

[metropolis909]

yeah im leaning towards the booster... i mean the truck stops perfect... just cruizing but second u give it a lil and hit the brakes it takes a few seconds...
i can get a booster for 100 my cost

 

[westtnfx4]

That's cheap^^^

 

[metropolis909]

yeah adavance autoparts has gives me like 20% off or sumthing like that. i would do a ford one but well over 200 i bet... i looked at rockauto.com and the motorcraft ones is 173... soo can only imagine what the dealer wants

 

[westtnfx4]

I hear it's a booger to change but idk...I haven't actually had to change one so I could be wrong

 

[metropolis909]

i looked at the pics of it it doesnt look bad.... haha idk im hoping i dont need to change it and it just the check valave thingy haha