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Even though the vehicle is a Ford pickup, this is more of a generic question because the brake booster is an aftermarket item that would probably fit anything. So here is the scenario. The initial brake application travel is boosted with easy pedal travel and good braking. After the initial pedal travel though - any attempt to further apply the brakes or modulate the brakes through a slowing or stopping event is unboosted and the pedal is very hard and braking quite difficult. If you quickly allow the brake pedal to come completely back up and start over, the initial pedal travel (only) is boosted again. What could cause these symptoms?
I don’t have a vacuum gage but I can get one. It is so consistent, the same whether the engine is accelerating or holding back (when there should be plenty of vacuum - right?). I was wondering if it might possibly be a faulty check valve?
Sorry folks, I left out an important piece of the story. The brake setup worked flawlessly for around four years before the issue I described developed.
I have one of those boosters on my 72. I never liked it from day one. I have the same master cylinder, too.
I will be going back to a stock setup, soon.
Probably not an ideal setup and is on the list of things to do. Just wondered if those symptoms rang a bell with anyone.
The chassis manuals detail how to trouble shoot the Ford booster/master. But even if you can determine what is specifically wrong. Where are you going to get the parts to fix it. Seems your only choice is to figure out what you have and buy another one like it.
There is a big advantage to using factory parts and buying the best quality the parts store has. My truck has power disc from 78-79 F150. I bought the best booster/master O'Reilly's had with a lifetime warranty. After about a year it developed a leak. I took it back and they cheerfully gave me a new one.
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