Lost power brakes?
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Elder User
Joined: Apr 2010
Posts: 518
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From: Mount pleasant, michigan
Lost power brakes?
The other day when i was last driving my truck, i slammed on the brakes because some ******* pulled out in front of me. When i did so i felt a pop in the pedal and lost the power assist. Now i have manual brakes, it has a new master cylinder on it and the motor runs fine with -20 hg manifold idle so it has no air leaks. The old girl's a 78 F150 4x4, 4" lift with 35's, whats my issue?
Elder User
Joined: Aug 2004
Posts: 796
Likes: 1
The vacuum assist booster works by way of one (or more?) diaphragms in there. If you heard or felt a pop it is very possible that a diaphragm broke. Very likely just need a new booster. I'm not real sure of any way to test them other than to apply vacuum and see if you have power assist. Since you still have brakes, and you have vacuum but you don't have power assist, seems like the booster is about the only thing left.
Elder User
Joined: Aug 2004
Posts: 796
Likes: 1
Press on the pedal without it running and it should be fairly firm. Use a hand powered vacuum pump to apply vacuum to the booster. If you cannot apply vacuum this means it is leaking, or if you can apply vacuum but the pedal doesn't get any easier to press, the booster is your problem.
