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Old 01-04-2010, 09:29 PM   #1
MrNick
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Default Master cylinder residual valve

I am planing on instaling a disc/drum mastercylinder in my rod. The one I have is for an 1981-86 mustang non-power brakes. How do I find out if this has a built in residual valve?
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Old 01-05-2010, 07:54 AM   #2
V8 Bob
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Default Re: Master cylinder residual valve

Internal master cylinder residual valves disappeared around 1974, because of the increased use of disc brakes (which never used residuals because of above-the-floor master locations), expander cups in the drum wheel cylinders (to prevent air from being drawn in during release), and cost. But an easy way to check any dual master (99% of all single masters had/have residuals) is to take a paper clip or similar small diameter object and slowly push it into the output ports. If you feel a spongy resistance, you are pushing against a residual. If none are present, the object will easily go into the master bore. Below is an exploded view of a typical dual master showing the residuals. FYI, I do recommend using a 10 lb external, or stock internal, residual in any drum system system, as it will help "tighten" the system with minimum pedal lose.
Bob
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Old 01-05-2010, 08:39 AM   #3
MrNick
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Default Re: Master cylinder residual valve

Thank you very much for the information. I knew that the later GM master cylinders had no internal residual valve but did not know about the later mustang ones. I plan to run a 10# residual valve to the rear and an adjustable proporting valve. A 2# residual to the front (the master cylinder is below the calipers) and a metering valve to the front.
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Old 01-05-2010, 09:12 AM   #4
V8 Bob
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Default Re: Master cylinder residual valve

Your brake plan is very good, except for the metering, or hold-off valve. These became popular in the 70's with the increased use of front discs. The theory was that by holding off the front pressure by about 100 psi, the rear drum shoes would overcome the powerfull return springs and contact the drums at about the same time the front pads contacted the rotors. The problem was, under certain conditions, the rears became too aggressive, and rear slide occured before the fronts, a complete no-no. They went away, and came back in the early 90's because pedal "feel" became important, but rear-only ABS prevented early rear slide, so no problems. By the mid-late 90's, 4 wheel ABS and 4 wheel discs with computor control became the norm, making prop and metering valves obsolete. Bottom line-there were days-weeks-sometimes months worth of vehicle testing to match proportioning and metering to production vehicles, and one of the most important goals was to prevent early rear slide. Using "fixed" prop or metering valves from a junk yard or the aftermarket on a custom vehicle is a crap shoot on how the braking will perform. My advice is to skip the metering, but use an adjustable prop valve, along with the appropriate residuals, IMO.
Bob

Last edited by V8 Bob; 01-06-2010 at 01:23 PM.
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Old 01-05-2010, 10:23 AM   #5
MrNick
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Default Re: Master cylinder residual valve

Thanks again. I had got my information from Tex Smiths book on hot rod chassis. I'm suprised that the book was published in 2002 and this information was not included. He still recomends the use of a metering valve.

My rod is a 4 banger track T quite light (1328# empty) with about 55% weight favoring the rear. Big and littles. 165-15 front, 235-15 rear.

When I got it, it had a single resivor wellwood master cylinder. I have it torn down now and I am doing some up grades.
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