Braking issue. 79 250 4x4
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Mountain Pass
Joined: Feb 2023
Posts: 122
Likes: 34
From: AL
Braking issue. 79 250 4x4
Driving around this evening. Pushed hard on brakes and worked fine. However backing into the garage after I got home, straight to floor and right at the end they finally worked. Brakes are firm when the truck is not running, but right to the floor when I crank it up. I can hear what sounds like a slight hiss from the master cylinder area but I’m lost. Help?
Moderator & parts slinger
Joined: Feb 2007
Posts: 50,239
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From: S/W Missouri, Polk county
Power brake booster unit is shot, that hiss is the diaframe leaking thru the firewall, you need a new one. You had brakes at the bottom because that was all foot power brakes NO power brake booster or NO "power brakes". Unless you have a major fluid leak, identified by a instrument panel red BRAKE warning light? Good luck locating a repop booster now days, they can be a sort of hard part to source. if you can get a loaded one (meaning new master cylinder AND power brake booster all ready together, might be the smart move. You going to hire out the replacement to a pro shop?
BBB https://www.battlebornbrakes.com/pro...ge-bore-master
BBB https://www.battlebornbrakes.com/pro...ge-bore-master
Laughing Gas
Joined: Feb 2011
Posts: 996
Likes: 318
If the pedal went to floor and there is no brake fluid squirting out anywhere, the master cylinder is bad. Bad booster or not there is no way the pedal goes to floor unless a fluid leak or internal MC piston seal failure.
If you buy a booster, do not give up the old one until the new one is in and functioning.
If you buy a booster, do not give up the old one until the new one is in and functioning.
Thread Starter
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Mountain Pass
Joined: Feb 2023
Posts: 122
Likes: 34
From: AL
Power brake booster unit is shot, that hiss is the diaframe leaking thru the firewall, you need a new one. You had brakes at the bottom because that was all foot power brakes NO power brake booster or NO "power brakes". Unless you have a major fluid leak, identified by a instrument panel red BRAKE warning light? Good luck locating a repop booster now days, they can be a sort of hard part to source. if you can get a loaded one (meaning new master cylinder AND power brake booster all ready together, might be the smart move. You going to hire out the replacement to a pro shop?
BBB https://www.battlebornbrakes.com/pro...ge-bore-master
BBB https://www.battlebornbrakes.com/pro...ge-bore-master
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