Tractor Hauler Brake Issue

Thomas(AB) · Apr 10, 2020

My tractor hauler is a 89 f250, 7.3idi.
Did some maintenance recently, front bearings calipers rotors pads. Rear shoes and a rebuild on the rest. New Master Cylinder couple years ago. Some sort of valve or device on the master cylinder that goes to the rear line. Cannot get fluid through this device. Is this a proportioning valve? How does this come apart for repair, local napa has no idea. A 93 or 94 f150 sitting in the yard has the same device. Tempted to swap and see if that solves the problem.....but the f150 isn't mine.
Anyways- whats the device called/whats it do?

used red MN · Apr 11, 2020

It may be the safety valve that closes one half of the system if there is a leak. Air in one half the system will cause this. Seems odd that it only is connected in the back line. If that is the case I don?t know if my method to reset it will work because I always thought it relied on pressure from the working side to reset it. My method is to pump the brakes up good. Hold it a bit, release it then quickly give the pedal a good stomp, almost to the point you think you will stomp it through the floorboard. When they trip they usually turn on the brake light in the dash. Start it up and check that.

Janicholson · Apr 11, 2020

Another way to reset some of them is to have someone push the pedal (Running to get vacuum boost) as hard as a stop from 60, while you crack an output line from that valve. The action can over do the problem and create the opposite, front in this case, system to close. If so then do that line more gently. Some can be done by looking at the warning light and with light pressure opening the ine to the working brakes at the valve, watching the light and pushing harder until the light goes out. tighten the line before letting completely off to avoid sucking air. No guarantee on this, do some more research on wht it is. Jim

RobCons · Apr 11, 2020

My 92 f350 has a rear antilock brake valve on the frame just below the master cylinder. They tend to malfunction over time. Corrosion and such. My truck had fluid at the rear but not enough pressure to do anything. I simply took the valve out of the system. Brakes work great now. No problem with rears locking up.

Steve@Advance · Apr 11, 2020

Worked on a Ranger about that year range, rear brakes would not build pressure.

Found one of the adjusters frozen causing the rears to need more fluid flow than the valve wanted to give them. I freed the adjuster, got them adjusted, but still could only get a small trickle of fluid, not enough to even bleed them for sure.

My conclusion was the valve was stuck. I could get good flow ahead of the valve. I'm sure a new valve would have fixed it but the owner didn't want to spend the money, so will never know.

He sold it to his grandson to take to Colorado. Couldn't stop that thing in a 1/4 mile!

Tractor Hauler Brake Issue

Thomas(AB)

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used red MN

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Janicholson

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RobCons

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Steve@Advance

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