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Discussion Starter · #1 ·
My '99 F250 had left front brake line failed without warning (installed from the factory the line rubbed on the frame - after 23 years it wore thru). When the line burst - fortunately right in front of my son's shop - the pedal went right to the floor leaving no brakes whatsoever. Also the brake warning light did not come on.

Replacing the leaking line and bleeding has the brakes working fine again on all 4 wheels. Disks and pads show more or less even wear at all 4 corners.

What concerns me is the complete loss of brakes with a single line rupture. Shouldn't the dual circuit system still provide partial brake function on the unaffected rear brakes? And shouldn't the dash warning light come on?

Is this an internal issue with the master cylinder, or is something else going on? The truck is 2 WD and has the 7.3 engine with a hydraulic brake booster. It has ABS only on the rear axle - near as I can tell the ABS works as it should.

Thoughts/advice are appreciated!!
 

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Sounds like something may be wrong with the master cylinder, unless you were way low on fluid, but even in that case the warning light should have come on. Maybe the bulb is burnt out?

Moving your post to Wheels, Tires, Brakes & Suspension where it'll be more on topic.
 

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You're right - in theory, the rear brakes should have been unaffected. I had the same experience as you did though. My alignment guy "bent" a brake line out of his way. When he put the tire back on, he failed to notice it was rubbing. I lost my front driver's side brake line on the way home. And, just like you, my pedal hit the floor and I had zero brakes. At 45 MPH with a line of cars at a red light. Fortunately, our parking brakes work pretty well especially combined with throwing the shifter into first.
 

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Discussion Starter · #4 ·
Sounds like something may be wrong with the master cylinder, unless you were way low on fluid, but even in that case the warning light should have come on. Maybe the bulb is burnt out?
You pretty much confirm the issue is with the master cylinder.

Reservoir was full to the mark when the line broke - it lost less 1/4" of fluid by the time I figured out the problem.

And yes the dash brake warning bulb is good - it illuminates while cranking and when the parking brake is set.
 

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The master cylinder has a spool in it between the two circuits. You may have had brakes on the good half of the system after the failure by pumping the pedal, which would refill the good half with fluid with the spool all the way to the end of the cylinder. I know it's kind of hard to try that when the pucker factor is high. :confused:
 
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