Hydroboost mystery

[ncup40]

76 crew cab dually, new calipers and pads on front, new wheel cylinders and shoes on the back also new master cylinder and hydroboost unit and a new power steering pump. after all of that the brake pedal is still hard as if there is no power assist and my mechanics are stumped, anyone have any ideas?

[Irish_Alley]

how long was the truck sitting?
was there fluid in it before?
have you made sure its getting to the right places (wheel cylinders and calipers)
do the brakes work?
is this a 4x4?


welcome from maryland

[ncup40]

the truck had a hard brake pedal when I bought it a couple of years ago and have just been replacing parts chasing this problem it is a two wheel drive and the brakes do work. most of the brake lines have been replaced as well and the brakes have been bled so many times with each new part that it is new fluid throughout the whole system but still have a hard pedal like there is no power assist

[VileZambonie]

The power steering is working correctly, belt tight, proper fluid type and level? With the engine off, pump the pedal about 15 times to bleed out the accumulator pressure. Press firmly on the brake pedal and start the engine and see if you feel the system charge, it should drop slightly and allow some pedal feel in your foot. Hydro-Boost does not feel like vacuum boost brakes so is this a new to you truck or something happened and now you are noticing a difference?

Give more info ie engine etc and post pics. Did they route the lines correctly?

[Irish_Alley]

my 91 crew has hydro boost. its pedal is firm as heck. in maryland a certified mechanic will inspect the truck and take it for a test drive. he has to verify that the brakes are working correctly. the total inspection is 2-3 hrs, and he passed my truck with the pedal feeling that firm. now if i drive anything else my car or another truck it feels like i have a leak cause the pedal is so soft