Am I supposed to have a proportioning valve?

[holyford86]

under hard braking my truck will lock up the rear tires and the front brakes don't seem to grab too well. the hard brake lines were a hack job when I got the truck, I replaced all of the hard line using what I removed as a guide. I'm running the 9 inch rear brakes, they are properly adjusted and they don't hang up. the front calipers are new, as well as the pads, and soft lines. the calipers are meant for a 92 explorer (easier to fit extended brake lines on due to the different location of the banjo bolt) but they fit just fine on the D28. there are no leaks or air in the system. Does the master cylinder have an internal proportioning valve or is there supposed to be something additional on the frame somewhere? This is on my 86 with a 6 inch lift, 33 inch tires, and a flatbed (FWIW I had the same problem with 31 inch tires and no lift) If there isn't supposed to be anything else I would imagine that my weight distribution would do it. (heavy front bumper, 2 batteries, OBA etc...)
Is there some kind of addition that I can make to the system to proportion it a bit better without installing one of the aftermarket proportioning valves? (different master cyl, etc...)

 

[holyford86]

anyone?

 

[AllanD]

That depends on what you think a proportioning valve is....

Most people point to something in their brake hydraulic system
and call it a proportioning valve.

Unless you are looking at a race car and the valve is made by tilton
you don't have one.

Most people are pointing at something called a pressure differential switch
which only detects a partial brake system failure andlights the "Brake system"
lamp in the instrument cluster.

"Proportioning" is accomplished in the relative sizes of the wheel cylinders at each end of the vehicle, and "tuned" with the internal spring inside the master cylinder.

If you rear brakes are prone to locking up I'd be thinking master cylinder or front brake problem

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[holyford86]

ok, that makes sense, thanks allan.

 

[okietheranger]

does that mean u have to run the master for the 9" brakes? i have the same problem

 

[nitrofan1]

I would look at the master cyl. If it's old and the former owner did a hack job on the brakes it's possible that they never took care of the brake system. Old fluid gets dirty and water logged causing rust and corrosion. The master cyl needs to be replaced if it's been there for a while.

Looking at what you use your truck for I'd recommend flushing the fluid at least once a year.

New master cylinders are available through most parts stores now vs rebuilt. They cost about 10% more than the rebuilt and less of a chance of a defect.

 

[AllanD]

No what it means is that ford used a variety of different bore sizes in both the master cylinders and in the rear wheel cylinders.


the caliper bore sizes being pretty much a constant because it's more expensive
to make calipers different.



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