proportioning valve

[junkyardjeff]

Did the F250 with disc brakes have a proportioning valve,I have 76 disc brakes with a 76 master cylinder on a 70 booster and even adjusting the push rod do not have a good enough pedal. I am thinking I will either have to get a F250 disc master cylinder if it has a similar proportioning valve or a 73 to 79 booster.

[junkyardjeff]

What I was trying to say is will a 70 F250 disc brake master cylinder work with a 73 to 79 proportioning valve.

[Ranchero50]

On my '70 F350 the proportioning valve is down behind the steering box and a real gem to work on. Mine also needed taken apart to reset the safety pin as my brakes sucked too. Does your brake warning lamp light up?

[junkyardjeff]

I have no brake light hooked up since its a 76 disc brake system in my 66 with a 70 booster

[ultraranger]

Not all brake valves are "proportioning" valves and when a factory brake valve does have a proportioning function, proportioning is only ONE function within the valve body assembly.

No '67-'72 Ford F100s came with factory front discs brakes. The valve on these trucks was a pressure differential valve.

Disc brakes didn't become optional on the Bumpsides until 1968 ('68-'72) and this was only on the F250s & F350s. These factory disc brake trucks had the same pressure differential valves as the trucks with all-wheel drums. The main difference was an inline, stand-alone metering valve to the front discs but, no proportioning valves were used in the Bumpsides.

(Manual) Front discs became standard on all 2WD F100s through F350s in 1973. Power brakes was optional. There were two brake valves in use on the 2WD trucks; a brass Weatherhead valve and a cast iron Kelsey-Hayes valve.

These contained a metering valve to the front discs, pressure differential sensing between the front and rear brake circuits and a proportioning valve to the rear drum brake circuit, all within the same valve body assembly.

The MC is just a manually actuated hydraulic pump that sends pressure through the system to actuate the brakes. The pressure differential valve or disc/drum combination valve has no real bearing on what MC is used with it.

[junkyardjeff]

I think I will make a 73-9 booster work so everything matches.

[PetesPonies]

People use wrong terminology all the time with this subject. very vehicle with a drum rear and disc front has a proportioning valve. But the proportioning valve is not what most think it is. Most are referring to the combination valve. Some combination vales have a proportioning valve built into it, along with some other things. But sometimes a proportioning valve can be separate and not included within the combination valve.

[HIO Silver]

Metering Valve
The metering valve section of the combination valve is required on cars that have disc brakes on the front wheels and drum brakes on the rear wheels. If you have read How Disc Brakes Works and How Drum Brakes Work, you know that the disc brake pad is normally in contact with the disc, while the drum brake shoes are normally pulled away from the drum. Because of this, the disc brakes are in a position to engage before the drum brakes when you push the brake pedal down.

The metering valve compensates for this, making the drum brakes engage just before the disc brakes. The metering valve does not allow any pressure to the disc brakes until a threshold pressure has been reached. The threshold pressure is low compared to the maximum pressure in the braking system, so the drum brakes just barely engage before the disc brakes kick in.

Having the rear brakes engage before the front brakes provides a lot more stability during braking. Applying the rear brakes first helps keep the car in a straight line, much like the rudder helps a plane fly in straight line.

Proportioning Valve
The proportioning valve reduces the pressure to the rear brakes. Regardless of what type of brakes a car has, the rear brakes require less force than the front brakes.

The amount of brake force that can be applied to a wheel without locking it depends on the amount of weight on the wheel. More weight means more brake force can be applied. If you have ever slammed on your brakes, you know that an abrupt stop makes your car lean forward. The front gets lower and the back gets higher. This is because a lot of weight is transferred to the front of the car when you stop. Also, most cars have more weight over the front wheels to start with because that is where the engine is located.

If equal braking force were applied at all four wheels during a stop, the rear wheels would lock up before the front wheels. The proportioning valve only lets a certain portion of the pressure through to the rear wheels so that the front wheels apply more braking force. If the proportioning valve were set to 70 percent and the brake pressure were 1,000 pounds per square inch (psi) for the front brakes, the rear brakes would get 700 psi.

[PetesPonies]

The metering valve section there is in error. Metering valves are on drum front brakes as well. Regardless of the type of breaking system, you do not want the front to dive when the brakes are applied.

[ultraranger]

Factory metering (hold-off) valves (when installed) only delay the initial application of fluid pressure to the front discs. Metering valves are not used on all-wheel drum brake vehicles. They are only used on certain factory disc/drum vehicles.

'68-'72 F250s and F350s with (optional) factory front discs had a stand-alone metering valve plumbed into the front brake circuit ('67-72 F100s were not available with factory front disc brakes). The metering valve was separate from the pressure differential valve and, the pressure differential valve used on the F250/F350 factory front disc brake trucks was exactly the same as the pressure differential valve used on the F100-F350 trucks with all-wheel drums. Ford trucks with factory front discs had metering valves. --Mustangs with factory front discs did not have metering valves on them for the front disc brake circuit. They only had pressure differential and proportioning valves. These items were were physically separate until they were combined into one valve body assembly in 1970. --metering, pressure differential sensing (and later, proportioning) were not combined into one valve body assembly on the trucks until 1973.

'68-'72 F250s/F350s with factory front discs didn't have a proportioning valve for the rear drum brake circuit. Proportioning didn't come into use on the factory disc/drum Ford trucks until 1973. Under normal braking, the proportioning valve is completely open and is not active (does not restrict fluid pressure rise to the rear drums). In a panic stop though, system pressures are much higher and the proportioning valve becomes active to regulate the rate of pressure rise to the rear brakes, in proportion to the pressure being applied to the front brakes.

[sargentrs]

Thanks for the lesson, Steve! So, to us laymen, if we've swapped over to front disc brakes from a '74 (like me), we should source a proportioning valve for a '73+ with disc/drum and the equivalent m/c? If unable to find one, the same '73 Mustang disc/drum prop valve would work too? This is one of the big gaping holes in my swap that I have yet to get a definitive answer.

[PetesPonies]

Ultra ranger, as a retired Autoshop teacher, I beg to differ about brake metering . . . metering valves have been part of the combination valve since at least the 50s, maybe earlier. They were all drum vehicles.

[ultraranger]

Ultra ranger, as a retired Autoshop teacher, I beg to differ about brake metering . . . metering valves have been part of the combination valve since at least the 50s, maybe earlier. They were all drum vehicles.

Metering is used with some early Fords that had discs on the front but not on Fords that had drums on the front.

The following is a diagram from my '68 Mustang shop manual. It shows the internal workings of the (drum/drum) brake valve (upper part of diagram. --valve in lower portion of the diagram is for a factory '68/'69 Mustang/Cougar disc/drum setup for an external proportioning valve). As you can see, the only internal component either valve has is a pressure differential valve spool. There clearly is no proportioning valve inside the valve body, nor any metering valve.



'68/'69 Mustang factory disc/drum brake valve with external proportioning valve shown immediately below.



This is the old drum/drum pressure differential valve from my '69 F100 (I have '77 F100 front discs on it now). The only movable component inside this valve is the pressure differential spool (there are no proportioning or metering valves inside it).



Diagram for the pressure differential valve and its location on a '67-'72 Ford F100-F350. --notice the stand-alone metering valve location. The metering valve would only be on a '68-'72 F250/F350 with optional factory front disc brakes. --if factory front discs weren't installed, the metering valve would have been omitted from the circuit.


Metering valve for a '68-'72 F250/F350 with optional factory front discs.



Other than the engineering number on it and the mounting bracket, my '69 F100 drum/drum pressure differential brake valve is identical to my old '68 Mustang drum/drum pressure differential brake valve.

Heavier vehicles like the trucks or a full-sized Galaxie with factory front discs would have had a metering function and a pressure differential function. A lighter vehicle like an early Mustang only had a pressure differential valve on an all-wheel drum brake setup or, a pressure differential function and a proportioning function on a factory disc/drum setup. The early Mustangs didn't have metering on any of their brake systems, regardless of their brake type. --proportioning and pressure differential sensing was combined into one valve body assembly beginning with the '70 model Mustangs but, their brake valves had no metering function either.

1970-up Mustang integrated style pressure differential/proportioning valve


Beginning in 1973, all Ford F100-F350 trucks came standard with manual front disc brakes. Power brakes was optional. '73 was the first year the truck brake valve functions were integrated into one valve body assembly --metering to the front disc brake circuit, pressure differential sensing between the front and rear brake circuits and proportioning was added for the rear drum brake circuit.

In the 2WD Ford trucks, there were primarily two disc/drum brake valve types used. One was a cast iron valve made by Kelsey-Hayes. It is designed for trucks 6800# and under. To bleed the front brakes out with this valve, the stem sticking out the front, for the metering valve, has to be pulled outward.

Kelsey-Hayes cast iron disc/drum metering, pressure differential, proportioning valve I pulled from a '77 F100.



Metering bleeding pin tool for cast iron K-H valve.



The other disc/drum brake valve primarily used on the 2WD trucks over 6800# was a brass valve made by Weatherhead. The pin for the metering valve on this one has to be pushed in, when bleeding the front brakes.

I pulled this disc/drum brass Weatherhead brake valve from a '73 F350.



Factory diagram of cast iron Kelsey-Hayes brake valve in lower half, brass Weatherhead valve in upper half of diagram.




Setup in my '69 F100 Ranger: 1975 F350 Bendix dual diaphragm booster, MC for a 1995 Ford Explorer (1-1/16" bore), OEM NOS disc/drum brake valve for a 1984 Ford truck, '77 F100 front discs.





....sometimes, even the teacher can learn something from the 'student.'

[PetesPonies]

You can link whatever pics you want, it's still wrong. Over and out son.

[ultraranger]

You can link whatever pics you want, it's still wrong. Over and out son.

Classic.

I guess Ford didn't know what was inside their own brake valves when they drew those pictures of the internals in the diagrams and, evidently, they didn't know what valve configurations they used on the various vehicles they produced.

--technically, in radio-speak, "over" means you talk now. "Out" means I'm through talking. That phrase is uttered a lot on T.V. programs and movies but in the real world, a person speaking on a radio wouldn't use that phrase with both those words in the same sentence.