Hi. Having a problem with my brakes. Last time I bled the brakes was maybe 10 years ago. I have a dual master cylinder under the floor. Disc front, and drum rear. I have a adjustable proportioning valve and a line going to the rear drum brakes from the master cylinder. It seems to be leaking a little at the knob, and fittings on that adjustable valve. Can I replace that valve with a 10 Lb residual valve for the rear drums?? Thanks..
Go for it and see what happens. If the rear brakes lock up to soon then you'll have to put an adjustable valve back in place. That's the basics.
Maybe I should just put in another adjustable valve. I would think by now those valves should have improved..
Keeps a little line pressure to prevent the wheel cylinder from fully retracting. Sent from my iPad using The H.A.M.B. mobile app
Residuals keep air from entering past the drum brake wheel cylinder cups during brake release, because of the strong shoe return springs.
Rsidual valve is NOT a replacement for a proportioning valve. 2 completely different functions. Look for a Wilwood proportioning valve. SPark
Adjustable proportioning valves are just a "patch up" for those who get out of their depth mixing and matching parts. They don't proportion, they only limit maximum pressure. Most OEM brake systems have the fluid mechanics slightly more rearward in their Fr/Rr bias. During less than ideal traction conditions [Mn snow] too much front bias would be dangerous at lower rates of deceleration [Front Lock Up] even with light pedal pressure [line pressure] So the Fr/Rr bias is set up for average driving conditions/deceleration. In ideal conditions, during an "Oh F**k" moment, there would be too much rear bias and rear wheel lock up. proportioning valves limit the maximum pressure and prevent rear wheel lock up when you try to stamp a foot imprint into the floor.
You can state an opinion on proportioning valves, but it should be based on facts, not falsehoods. U.S. OE production proportioning valves came along with front disc/rear drum systems because of the higher (about 2:1) line pressure requirements of disc brakes, compared to drums. Adjustable proportioning valves provide the owner of a custom or non-stock disc/drum-disc/disc system a practical means of balancing the front/rear brake bias if needed, something a fixed value prop valve may not perform as well. Labeling them "a patch up for those who get out of their depth" is rude, and frankly offensive. Never mind that some early mid '60s single system disc/drum cars came with adjustable prop valves, or that I and many other brake test techs used them to arrive at psi values suitable for fixed-value valve OE production. I guess we were all "out of our depth". True proportioning valves, whether fixed or adjustable, really do proportion, by definition. They allow full master cylinder pressure until the fixed or adjustable knee or crack point is reached, then proportion a percentage of increasing master cylinder pressure to the rears. Fluid mechanics slightly more rearward in their Fr/Rr bias. Really? Fact is cars and most light trucks always have larger front brakes, because of the normally heavier front axle, and dynamic weight shift towards the front during braking. The front brakes should do most of the braking, no matter the traction conditions. You never want the rears to slide before the fronts, and is the reason most disc/drum and disc/disc production vehicle had proportioning valves up to the '90s, when advanced ABS took over that function.
It always amazes me how much misinformation there is about brake systems. I hope these are not the same people building cars.... Sent from my iPhone using H.A.M.B.
Kudo’s to the original poster for asking the question I think...afterall thats part of what the site is meant to do by helping one another with problem solving and questions so that when are cars are on the road carrying ourselves and loved ones they are not unsafe rat bag POS.
I admit,the use of the term "more rear bias" isn't the best use of words [it is a Road Racer term for dialing a car in] eg: "You need a bit more rear bias because the fronts are locking" Road Racers use a balance bar which is true proportioning. In ideal dry conditions there is more weight transfer to front so more front bias is needed [bigger brakes to the layman] On a wet surface there is less deceleration so less weight transfer, in this situation a car set up for the dry would lock up the fronts early so more bias is dialled into the rear. [trying to get 4 wheels to brake at lower G's] Put a clamp on your rear brakes and try it yourself , the front brakes will haul up OK[ish] in the dry, but lock up early in the wet.[do this on a skidpad] You'll also notice there is less pedal pressure in wet conditions. What manufacturers do is set up the Fr/Rr bias for less than ideal conditions [less pedal pressure] for most driving conditions, then ADD a "proportioning" to prevent rear lock up when extreme pedal pressure is applied. If you put pressure gauges on the front and rear brake circuits you'll soon discover that the line pressures are equal just about all the way across the range , Until you really stand on it. Then the rear circuit reaches a limit and stays there while the front circuit continues to climb in pressure. A proportioning valve is basically a Relief Valve that closes at a set pressure [instead of opening] Any fluid "downstream" of that valve is trapped at that pressure until it opens again ,so there is still rear brakes with the valve closed. Adjustable proportioning valves just have adjustable spring seat pressure on this "relief valve" Except for cars with a twin master cylinder system with a balance bar, the only proportioning is done at the wheel cylinders [fluid mechanics] This is actually proportioning the "clamping pressures" If you understand the Maths involved [There is a Shitload] ,then most people are "out of there depth" when modifying brake systems. The worst culprits are people selling Race front brakes for daily drivers
Okay. Pretty much everything you just said is out of my league. All I want is for my brakes to function. I have a dual master under the floor. I have disc brakes front, and drums rear. The rear end is a Ford. The front is Mustang II . I have residual valves for the front, and the rear. I got a lot of my information from How To Build a Street Rod. The book told me to get a adjustable proportioning valve. A fellow Rodder to me to leave the valve wide open. I just want the car stop when I put on the brakes. My learning skills are not the best, so all of the reading goes way over my head. What would you suggest I use??
The Jalopy Journal
