need advice on proportioning valves

proportioning valves

I converted my 69 to front disc.Bought the adjustabl prop valve from CJ pony.Got the brakes all bled and everything is working well.75 mustang II

Manual proportioning valve is the safest bet. Sumit sells one for $35+$11 handling. If you have standard 3/16" brake lines, line fitting will be needed. Fixed proportioning valve taken from other car is nearly 100% likely that your brakes will be inefficient. You end up braking too much or too little with rear brakes, which will cause premature wear of brake pads on either end, and longer stopping distance.

SSBC now makes a distribution block that has a built in prop valve. for about $100. You can go that route, or just tee in a generic prop valve from Wilwood or Summit on your rear line circuit that allows you to reduce pressure to the rears until your fronts lock up before you rears in a panic stop.

When I did the swap from 4 drums to 4 discs in my 67, I just left the Proportioning valve as is. Worked fine. (manual discs)

D.Hearne said:

When I did the swap from 4 drums to 4 discs in my 67, I just left the Proportioning valve as is. Worked fine. (manual discs)

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4 wheel drum cars don't have proportioning valves. The balance is achieved by varying the bore diameter of the wheel cylinders and the leverage aspects of differently sized drums.

gsxrken said:

4 wheel drum cars don't have proportioning valves. The balance is achieved by varying the bore diameter of the wheel cylinders and the leverage aspects of differently sized drums.

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Then what was that metal block bolted to the fenderwell that all the lines went into-out of ? And why did my brakes work fine after the swap, that also included a different master cylinder ?

D.Hearne said:

Then what was that metal block bolted to the fenderwell that all the lines went into-out of ? And why did my brakes work fine after the swap, that also included a different master cylinder ?

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That's just a fluid distribution manifold, distribution block in 'brake speak'. No valves or anything inside it.

D.Hearne said:

Then what was that metal block bolted to the fenderwell that all the lines went into-out of ? And why did my brakes work fine after the swap, that also included a different master cylinder ?

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D., you are probably describing the distribution block, which is a brass block with several ports on it for MC in, Rear line out, and usually two front lines out. It was just a means to route fluid. Some distribution blocks also have a little shuttle valve in them to trip the brake warning light on the dash when there is leak on one of the axles.
I just googled and landed on this site, which also makes the point: http://www.stangerssite.com/brakevalve.html
"This section deals with the Proportioning Valve used primarily on the 1965 & 1966 Ford Mustangs with Front Disc Brakes. It mounted on the drivers side rear fender apron, between the shock tower and the firewall, under the hood hinge. This is not to be confused with the Distribution Block, a brass piece that distributes the fluid coming from the master cylinder.
A Proportioning Valve is only found on cars with disc brakes. It is spliced in the brake line running from the master cylinder to the rear wheels. Its purpose is to dampen and reduce brake pressure going to the rear brakes."

On my disc brake 69, you can see the proportioning valve separate from the distribution block in this pic: http://www.geocities.com/gsxrken/Mustang/Mustang2/100_2259.jpg

EDIT: as for why your car works well without one, you may just be lucky! Most OEMs built in bias with caliper bore sizes where the rear brakes only have about 50% of total piston bore diameter as compared to the front calipers. So right there, even without a prop valve, you have half the force at the rear. Depending on your front and rear caliper selection, you may have landed on a decent combination. Have you ever tracked your car, or even better to show it, tracked your car in the wet? At extreme braking, like on the end of a straight into the infield, you may find your tail-end moving around back there before the front locks up. Not good. On the street, you might never notice it. Hey if it works for you, leave it alone.