'79 F700 Brake Problem
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Tuned
Joined: Oct 2007
Posts: 294
Likes: 6
'79 F700 Brake Problem
Truck has what I think is called a Hydrovac System. It has the strange symptoms of; push brake pedal once, truck brakes well, pump a second time it still stops but pedal seems to "push back" some, pump a third time and the brakes are GONE. Very weird.
I took it to the local tire and brake shop and they supposedly bled it and checked for vacuum leaks. When I took it for a test drive it behaved exactly as before. Anyone ever had this experience or understand the system well enough to know how it can brake well on the first pump and end up with no brakes on the third pump? Thank you.
I took it to the local tire and brake shop and they supposedly bled it and checked for vacuum leaks. When I took it for a test drive it behaved exactly as before. Anyone ever had this experience or understand the system well enough to know how it can brake well on the first pump and end up with no brakes on the third pump? Thank you.
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Tuned
Joined: Oct 2007
Posts: 294
Likes: 6
It does. Seems like it is between 15-20 inches on the gauge. It will take a little bump down when I hit the brakes but it stays fairly constant in that area when it gets warmed up. I do note that after start-up it takes a few minutes for the vacuum to build. I will pay closer attention to it next time I run her.
Laughing Gas
Joined: Jan 2008
Posts: 1,027
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Send the booster to Capitol Clutch and brake in Sacramento CA for a rebuild... you wont be disappointed
Capitol Clutch & Brake
Capitol Clutch & Brake
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Tuned
Joined: Oct 2007
Posts: 294
Likes: 6
Send the booster to Capitol Clutch and brake in Sacramento CA for a rebuild... you wont be disappointed
Capitol Clutch & Brake
Capitol Clutch & Brake
Laughing Gas
Joined: Jan 2008
Posts: 1,027
Likes: 4
but yes they are pretty simple inside
Ford Parts Specialist
Joined: Nov 2006
Posts: 88,826
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From: Simi Valley, CA
Truck has what I think is called a Hydrovac System. It has the strange symptoms of; push brake pedal once, truck brakes well, pump a second time it still stops but pedal seems to "push back" some, pump a third time and the brakes are GONE. Very weird.
I took it to the local tire and brake shop and they supposedly bled it and checked for vacuum leaks. When I took it for a test drive it behaved exactly as before. Anyone ever had this experience or understand the system well enough to know how it can brake well on the first pump and end up with no brakes on the third pump? Thank you.
I took it to the local tire and brake shop and they supposedly bled it and checked for vacuum leaks. When I took it for a test drive it behaved exactly as before. Anyone ever had this experience or understand the system well enough to know how it can brake well on the first pump and end up with no brakes on the third pump? Thank you.
Hydro-Vac is a remote mounted P/B booster, usually located on the frame rail.
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New User
Joined: Sep 2020
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our 74 f600 does the same thing when pedal gets hard and "pushes" i push clutch in and rev engine ,vac comes back up and i have power pedal again....i think booster has pin hole somewhere
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