Brake Failure Question
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Mountain Pass
Joined: Aug 2019
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Brake Failure Question
1993 F250 4WD, 351W A week or so ago one of the rear brake lines rusted through. Fluid poured out, no brakes. etc.I had a new line installed and all was well. Today, a few days after getting it back, I pushed the pedal real hard at a stop. After a second or two it dropped to the floor all of sudden! Luckily I was close to home and could make it back with ebrake. So I was expecting to come home and see the master cylinder out of fluid. But it's not, it's full. And I don't see a leak under the truck. When I push the pedal, it drops to the floor and if I hold it there hard, there's a little braking action, but minimal. So, since it doesn't appear to be a leak, what's my next most obvious "It must be this" repair?
Logistics Pro
Joined: Aug 2010
Posts: 3,716
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From: Chillicothe
Probably that master cylinder is bad. Usually what happens, when you lose a line and the pedal travels further than normal, the seals get damaged. So that is where i would start. Usually easier to initially bleed them outside of the truck. Lool for a YouTube video about "bench bleeding a master cylinder ".
Lead Driver
Joined: Jul 2017
Posts: 9,569
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From: San Jose, CA
Would not hurt to even before you have a replacement part, remove the master cylinder from the booster just to look behind it and see if the fluid is leaking out into the booster.
If it is then over time the booster diaphragm can be damaged from the brake fluid.
But it’s also a dead giveaway that your master cylinder is toast, so another good reason to remove it.
You don’t have to disconnect the lines or anything fiddly like that. Just undo the nuts and pull it forward slightly.
I can’t say for certain on your truck, but most of them of this vintage have enough flex in the lines that you can separate the master from the booster without too much trouble.
If it is then over time the booster diaphragm can be damaged from the brake fluid.
But it’s also a dead giveaway that your master cylinder is toast, so another good reason to remove it.
You don’t have to disconnect the lines or anything fiddly like that. Just undo the nuts and pull it forward slightly.
I can’t say for certain on your truck, but most of them of this vintage have enough flex in the lines that you can separate the master from the booster without too much trouble.
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Mountain Pass
Joined: Aug 2019
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Just circling back on this. The front driver's side brake line rusted through and caused the pressure loss. Had it fixed.
I should probably replace all the lines.
Thanks for the thoughts, everyone.
I should probably replace all the lines.
Thanks for the thoughts, everyone.
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