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So, are you saying that the car will not try to change back for front when the rears lock up first?

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what I'm saying is the type of master cyl for your application create the pressure for the front and rears, different stroke lenghts inside the cyl is where it's at, also sizing of pistons
what the heck do I know, I'm just a freaking clown!
lets try this, say you have a stock system that everyone has, you want more pressure to the rear, so you buy a adj valve put it in do you put it in after the prop valve or before? If you put it in after how in the world , if what he says is true , then how can you get more pressure?
In the old days of 1 line master cyl you had same pressure front and rear, safty gurus decided after several brake line failures and deaths, the system needed to be seperated and a 2 line master cyl evloved . and also it was required that the system needed a warning that would tell the driver when something was wrong with that system thus the prop valve it help in 2 ways , it seperate the front and back , and serves as a warning lite activator.
after that I'm uneducated lol

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LOL...I don't believe you are the clown in question. In essence, I believe you are correct (see my post above).

If you retain the factory valve, the adjustable valve normally goes in the main line running to the rear

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Very well said Supercuda , unfortunately your info generally falls on deaf ears in these forums when it comes to these brake problems/questions/applications/modifications threads...


IMHO that's a nice Duster the OP has, if it was mine, I'd be outfitting it with a rear disc set-up, sized, based on what caliper volume I have upfront, then it would be "OK" to ditch the PV valve, otherwise if your going to keep the antiquated rear drums, get your PV replaced with a properly functioning unit...

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I seem to have started a bit of a firestorm here. Sorry for that, all.
Thanks Dayclona for the complement about my rolling parts house. I thank you all for your advise and opinions. Jim V. has graciously let me use one of his (dare I use this term) prop. valves to see if it's my repop valve that's giving me all the headaches.
To help clear things up a little, I don't think I was ever going to entertain the notion of going without a prop. valve. Basically was just a query. Just thought I'd interject my thoughts here while theirs a lull in the lobbing of criticisms.
Thank you all again. Now lets all play nice.

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<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.

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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

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I thought perhaps I had dreamed it up, or it was from a Buick, or such, but, the information is contained in the 9th edition of the Mopar Chassis book by Larry Shepard/Michael Gingerella. I believe this is the latest edition. Pages 347/348

On the other hand, this refers to two specific master cylinders-Part#s P5249270 and P5249271

Therefore, the comment may well be wrong in the general context with regard to the units that came on the cars originally.

Here are a couple of pics...sorry for the fuzziness-too little light at the moment and too much shake, but, I am sure you have the book and can check if you are interested.

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<snip!> My '71 340 Duster came with K/H (Power) front four piston caliper disc/rear drum brakes. When I bought the car, the power booster was off it. Everything else was intact, and functioning very well. I even plumed in a line lock and went drag racing (I've removed the line lock during this restore). I replaced the org. MC with your aluminum MC you sell here a few years ago. Still everything stopped just fine. My trouble came when, while restoring the car, I replaced the K/H prop./distribution valve with an after market new one I found being sold by a well known Mopar parts vender. When I got everything back together and tried to stop the car, it just didn't want to stop very well. It felt like I just didn't have enough pressure to the Calipers/ drums to do a good job. I pressure bled the system (twice), and bench bled the MC. The peddle felt great, no slop, or fade. I can power out of the brakes, when fully applied (never been able to do that before). My question: given all the variables I described above, could the prop./distribution valve be the culprit? I have since rebuilt me K/H prop. valve (mostly just cleaning it up real well), and intend to place it back into the system to try it again. What do you think?
Thank you,
mike

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Thanks again for your reply.
I do not intend to put the power booster back on. I like the feel of the man. brakes (besides, I don't think my cam choice in my 416 would support enough vacuum for it anyway). I did bench bleed the M C before I put it into the system. Then ( I didn't mention this part in the first communiques above) bled the system with my wife (she's a real trooper) pumping the brakes, while I went from wheel to wheel. Then I did the two power bleeds later. I read your suggestions and I think I see what your getting at.

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The so called bias is the reservoir volume(from what
I have been told)... nothing to do with valve bias...
if you look/measure the bore of the master you will
find 1 bore size in there not 2 which would change
the bias... I have been running the alum master on
both my race car and my street rod without any DIST/error
in system valve for years... on the race car I have
disc/disc but with the lines on the master reversed
for the volume(front reservoir to the front brakes, rear to
the rears) with a adjustable valve(prop valve) on the
front brakes.... reason its on the fronts.... the
small tires CANT take the brake force that the BIG
rear slicks can on a pedal spike... quick lesson...
the adjustable prop valve JUST SLOWS THE FLUID...
given enough time the pressure will equal out... so
with the prop on the front tires it slows the spike
and allows the rear tires to do MOST of the braking
(and YES I did work in the brake lab for Chrysler
for some time)... but MOST of my time was in the
fuel and exhaust lab

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A good discussion of proportioning and valves...

prop valve tech

The '60s FSMs called for the valve to output a constant 360 to 405 PSI with a constant 500 PSI input.

At some lower pressure (varies by model, or adjustment on adjustable valves) the rubber "stage" seal does not close, so it is basically straight-thru. Once the set pressure is reached, it is, effectively, a small piston pushing on a larger one, reducing pressure by the ratio of (the area of) one to the other. If it "equalizes", there's internal leakage (which may well be common, since most stops only last a few seconds and these weren't precision implements!)

Again, the bulk of the proportioning was done by the ratio of F/R mechanics and hydraulics, as it should be. On a typical '60s Mopar, the fronts do 60-65% of the work.

Rick

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think you will need the proper residual valve for the drum brakes along with the prop valve---the residual is set at about 12" column pressure---this keeps your shoes in close proximity to the drums so that you dont have to pump up your brakes everytime you stop



Not saying I do or don't need it, but I've never had this in the past ever since I've owned the car. It always stopped just fine (well, fine for a 40 year old car). Is their any pics, or a place I can see what this looks like?
Thanks.