Many people buy a booster/(rebuilt) MC combination and often the (rebuilt) MC is mounted to the booster when they arrive. Out of naivety, they simply install the MC/booster on their vehicle and often it results in problems --brake drag or, a long pedal travel.

Number one, DON'T buy rebuilt MCs unless you want to be changing it out again in about a year (give or take). Rebuilds are often short-lived and frequently have high failure rates.

Brake drag or a long pedal travel is most often caused by improper adjustment of the tip on the booster to MC output rod. Don't assume that the booster/MC combo was adjusted correctly by the rebuilder.

All power brake boosters should be adjusted for the particular MC you are installing on it. Here's a simple procedure that explains how to measure and set the length of the booster out put rod to the MC.

http://api.viglink.com/api/click?for...FMMBAK-1r1.pdf

After you have the booster output rod adjusted for the MC that will be going on it, the MC needs to be bench bled before it's bolted onto the booster for the last time, prior to plumbing it up. --if you're making your own lines, you need to adjust the booster output rod, then fab up your lines and then bench bleed the MC. Otherwise, it's just going to make a big mess if you bench bleed, install the MC, THEN start fabbing up your lines.....


Types of brake valves used (whether factory or aftermarket) will just come down to a personal preference. Manually-adjustable brake valves have a variable pressure rate adjustment. This ranges from 100% open (unrestricted pressure) to about 57% restriction. Set for full restriction, a manually-adjustable valve will still be around 43% open.

However, you should realize a proportioning valve (whether factory or aftermarket) does nothing under normal driving circumstances. In this situation, the pressure being applied to the front brakes is the same as the pressure that's being applied to the rear brakes.

In a panic stop though, line pressures are much higher than under normal braking. This higher spike in line pressure acts on annular ends of the proportioning poppet valve. The elevated system pressure overcomes the rated tension on the poppet valve spring and causes the valve to move over and begin restricting the pressure rise in the valve body passage to the rear brakes, in proportion to the amount of pressure that's acting on the front brake circuit.

Factory brake valves are calibrated to operate at a specific pressure, at a specific percentage of pressure rise, for a specific vehicle application. Obviously, a Bumpside using Dentside brakes isn't a Dentside. However, using brake valves from/for a Dentside truck of like size and series with a similar size and series Bumpside will be very comparable to each other and won't result in a gross mismatch of how the brakes should operate.

Manually-adjustable proportioning brake valves are not D.O.T. approved. Many companies sell them to the general public but they know most people don't have a set a brake gauges to set the M-A proportioning valve with and probably most wouldn't know what pressure to adjust the valve to if they did have a set of gauges. Vendors get around this with the disclaimer that the valve is for racing purposes. --the warning will go something like this, "WARNING - Adjustable proportioning valves are designed for tuning and balancing custom brake systems on performance, racing, and other types of special purpose vehicles. They are not designed as direct replacements for any OEM application."

OEM Ford brake valves from/for most Dentside trucks will have a metering function to regulate fluid pressure to the front discs, a (factory set) proportioning function to the rear drums and a pressure differential brake warning circuit in between the front and rear brakes circuits.

The type of valve you use is just entirely up to you. However, beware that aftermarket manually-adjustable proportioning valves do not contain a metering circuit or a pressure differential safety circuit within their valve body assemblies.


This is the setup I installed in my '69 F100 Ranger: 1975 F350 Bendix dual diaphragm brake booster, new (not rebuilt) 1-1/16" bore MC for a '95 Ford Explorer, OEM NOS 1984 Ford truck disc/drum brake valve, 1977 F100 front discs/suspension. Stops my truck exceptionally well. --prior to adding the front discs and this MC, I had a factory cast iron 1.00" bore MC on the F350 booster with 4-wheel drums. Braking was better with the booster added but still wasn't all that great. Before that, I had 4-wheel drums with a manual 1.00" bore MC that were on the truck when I bought it. Braking really sucked then.


In the process of plumbing the MC to the disc/drum brake valve




Everything plumbed up and the brake system fully functional.

 

Excellent post ultraranger I appreciate it so much. I looked at your other posts too for vacuum boosters. Lots of details. I ordered the same m/c you have from NAPA.

Hopefully I'll get my rear brake pump-up/drag fluid not returning problem handled with new m/c and proportioning valve.

Very enlightening what you said about adjustable proportioning valves not metering as well as stock OEM Factory valves in a panic stop.

 

"Metering" or, "hold-off" is a function of the front disc brake circuit of the brake valves on the Ford trucks with factory front discs. All-wheel drum brake systems don't have metering or proportioning functions.

Disc brakes react instantaneously when you step on the brake pedal. Drum brakes do not. A drum brake wheel cylinder has to fill with brake fluid, push the wheel cylinder pistons outward and then the shoes have to overcome the tension of the retracting springs, before the shoes can make contact with the friction surfaces of the drums.

If the truck disc/drum brake valves didn't have a metering (hold-off) function to the front disc circuit, the truck would have a tendancy for the front end to have excessive 'dive' when you applied the brakes. The metering function of an OEM brake valve has a preset pressure rating to momentarily delay pressure from being applied to the front (disc) brakes. This gives the rear drum circuit a chance to unseat the shoes, overcome the retracting spring tension and force the shoes toward the friction surfaces of the drums.

--note, Ford Bumpside/Dentside trucks and full-sized Galaxies, for example, of the same era had metering valves for the factory front disc brake circuits. Early (lighter) Mustangs with factory front discs, however, did not have metering valves.

Manually-adjustable proportioning valves don't have a metering function nor do they have a pressure differential function. They only have a proportioning function that's manually set. It's not that M-A proportioning valves don't function as well as OEM brake valves. The main thing is the majority of people adjust the M-A proportioning valve by 'feel' or the seat-of-their pants. Your butt isn't very scientific when it comes to accurately dialing in the correct pressure setting and percentage of proportioning rise adjustment on the valve.

In the earlier years, when I was fooling with brake systems/disc brake conversions, I used to install M-A proportioning valves. A number of years ago though, I stopped using them and instead, began installing OEM brake valves. This was just a choice of personal preference. My reasoning for this is the Ford engineers had already put the engineering into the OEM valve calibration and it takes the work out of trying to GUESS at the correct adjustment of a M-A proportioning valve.

Without knowledge of what the knee-point setting and percentage reduction of the proportioning valve should be set to for a particular vehicle and, without the equipment to be able to actually read the pressure setting, it's much more likely a M-A proportioning valve will either be set above, or below, the true ideal setting of what it should be set to.

Some older disc brake conversions I had done, back when I used to install M-A proportioning valves.

1965 Ford F100 dual reservoir MC and front disc brake conversion.


1968 Mustang being plumbed for 4-wheel discs.





1956 Chevy Bel Air


1965 Mustang fastback 4-wheel disc brake conversion.


1965 Mustang 4-wheel disc brake conversion



General application of how a basic OEM disc/drum combination brake valve works.

 

update: I read the PDF doc on booster rod length I was .100 too long so I shortened it up and left a .015 gap and so far the rear drums are not stacking up pressure. Thanks for that doc it saved my sanity what ever is left.

 

Glad the instructions helped with your brake problem. That's what the information was presented for.