Quote:

<snip>Mopar used two basic m/c proportioning ratios according to the literature. One with 69/31% distribution and the other, I believe, was 67/33%.

This leaves us with trying to play with wheel cylinder size or an adjustable valve after we start changing up things with regard to brake size, brake composition, tire size/tread composition, and spring rates, etc.

Give the number of variables available to us today, I personally think that an adjustable valve is the easiest means of dialing in braking, but, opinions will surely variable.

Sorry, that I had difficulty discerning technical intent from within your rant.



I have no idea where this split/bias m/cyl info grew from, but I can tell you this: Every muscle-era Mopar I have ever investigated uses a straight-bore master cylinder, 50/50 distribution. Period. This error was fixed in later MP catalogs.

I haven't read everything above, so forgive me if some of this is redundant...just some info and factoids which I hope you find useful...

Combination valves are a combo of the safety switch / tee, a prop valve, and a metering valve. The purpose of the metering (standoff) valve is to prevent the front brakes from applying until the resistance of the rear shoe return springs has been overcome -- to prevent early front wheel lockup on glare ice.

If going to an adjustable prop valve, and you have a block/tee with a built-in prop valve, the stock valve must be "gutted" from the block. You only want one prop valve.

Getting the proportioning close by juggling wheel cylinder / caliper bore sizes is the preferred way to go. Prop valves don't "cut in" until there's a few hundred PSI (varies by model), often too late (!) on slippery surfaces. And you don't ever want both rear wheels locked. (That's why RWAL was introduced).

Factory setups of the '60s and early '70s were compromises. 440 Road Runner coupes used the same prop parts as 6-cyl Satellite wagons, and the F/R weight distribution couldn't be more different. Getting your F/R proportioning dialed in precisely makes a HUGE difference in stopping distances.

Another way to change proportioning is via drum / rotor diameter. Generally, if you swap a '60s / early-70s Mopar to 11.75" cop rotors, you've come close. 7/8" rear wheel cyls., and an adjustable prop valve, and you're within 20 feet or so (from 60 MPH) of a modern ABS performance car.

Lining material / friction coefficient / temperature / tire size / width / tread compound (etc.) also figure into the equation. That's why race cars typically have the prop valve (lever type) where the driver can adjust it during an event!

Bendix Duo-Servo (on almost all '62-'89 RWD Mopars) rear brakes have so much self energizing action that, especially with a power booster, even Mario Andretti would have tough time stopping straight. About all you can do is be on your toes -- literally -- threshold braking.

Rick