Porportioning valve needed?
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BillGrissom
Well-Known Member
May not be essential if the the front and rear disk setups came in the same kit from a company like Wilwood, all designed to work together, and your car is stock. Otherwise, smart to install an adjustable prop. valve and adjust the rears so they don't lock up until just after the fronts skid (test in wet parking lot). Even if your front & rear tires are different (wider rears, etc), it won't be stock.
Of course, if the rear disks are just for show (their main value) and your car will be a trailer queen and never drive faster than 10 mph at a show, no need for anything special.
Of course, if the rear disks are just for show (their main value) and your car will be a trailer queen and never drive faster than 10 mph at a show, no need for anything special.
roylerumble
Well-Known Member
I'm doing the same thing. Willwoods on the front and rear. Bill Reilly doesn't think its necessary if you go with the willwood master. However, I bought my master from Cass at Dr. Diff, and if memory servers me correct, he thinks a adjustable valve placed as close to the factory prop valve would be a good idea. I don't think they cost much, so I'm going to plumb one in.
I have four wheel discs with the MP aluminum master cylinder and NO proportioning valve. Pedal is rock hard and the brakes will throw you through the windshield.
I would only run one if it is needed, and you won't know that until you drive it. It is better to size the calipers to achieve the correct bias than it is to use a prop valve. On a 4 disc system I would be much more inclined to use an LBS than I would to use a p-valve. Think of it as a pressure delay valve, it slows the pressure rise to the rear brakes so that when they have the least traction they have the least braking pressure, but when they have more traction they have more braking pressure.
http://www.dpiracingproducts.com/lock-resistant-brake-system-lbs/
Adjustable p-valves do not adjust the rear brake pressure. I know everyone thinks that, and everyone is wrong. They have a "knee" in their pressure-in/pressure-out curve. P(out) = P(in) until you reach the knee point. Once past the knee point P(out) = ~.6*P(in) What you adjust is where that knee point is, not the pressure ratio.
http://www.dpiracingproducts.com/lock-resistant-brake-system-lbs/
Adjustable p-valves do not adjust the rear brake pressure. I know everyone thinks that, and everyone is wrong. They have a "knee" in their pressure-in/pressure-out curve. P(out) = P(in) until you reach the knee point. Once past the knee point P(out) = ~.6*P(in) What you adjust is where that knee point is, not the pressure ratio.
txstang84
Well-Known Member
...to expand on ntsqd's statement...
http://www.stoptech.com/technical-support/technical-white-papers/proportioning-valves
It talks about the knee point toward the bottom in "Proportioning valve selection".
While it technically doesn't adjust the brake pressure as you assert everyone assumes is wrong, the end result of adjusting the "knee" point is altered pressure rate to the back brakes compared to brake pressure rate to the front.
...kinda like the big hoo-hah about the sequestration; it didn't actually cut spending-it cut the rate of acceleration of spending. Congress still spent more money compared to the year prior, but the end effect was many programs didn't receive money they thought they would have based on previous spending rates; ergo the observable effect was they kept spending on frivolous programs but killed others in the former's favor.
http://www.stoptech.com/technical-support/technical-white-papers/proportioning-valves
It talks about the knee point toward the bottom in "Proportioning valve selection".
While it technically doesn't adjust the brake pressure as you assert everyone assumes is wrong, the end result of adjusting the "knee" point is altered pressure rate to the back brakes compared to brake pressure rate to the front.
...kinda like the big hoo-hah about the sequestration; it didn't actually cut spending-it cut the rate of acceleration of spending. Congress still spent more money compared to the year prior, but the end effect was many programs didn't receive money they thought they would have based on previous spending rates; ergo the observable effect was they kept spending on frivolous programs but killed others in the former's favor.
txstang84
Well-Known Member
Pretty cool device...but for many on here, an adjustable P/V is about a third the cost of the LBS. And while you're correct that sizing calipers is a much more appropriate way of biasing the brake pressure based on demands of the vehicle, again, most folks in this hobby are looking for something that will bolt on easily without having to calculate the math or fabricate custom brackets...more to the point, something that already exists from a salvage yard or off the shelf for a reasonable amount of money or something in a kit form that takes all the research and does it for them.
I commend your method but not everyone sees it that way.
I don't think that's quite right. It doesn't adjust the pressure rate, it doesn't adjust the pressure. All that it adjusts is where in your pedal effort do you go past the knee point and start reducing rear brake pressure. More "rear brake pressure" simply means that more of the pedal stroke is in the 1:1 zone and less of it is in the ~0.6:1 zone.
I'm not saying that everyone is wrong out of spite. There are many things where the mis-information about something is taken as the gospel (i.e. "DOT Approved") when it is actually wrong. No fault of those who thought it correct, they were going on the best known to them info.
I was going to also mention that the type or brand of master has (excluding GM's stepped bore m/c's) no, zero, effect on brake bias. The type of linkage driving the m/c can, but not the m/c itself.
I'm not saying that everyone is wrong out of spite. There are many things where the mis-information about something is taken as the gospel (i.e. "DOT Approved") when it is actually wrong. No fault of those who thought it correct, they were going on the best known to them info.
I was going to also mention that the type or brand of master has (excluding GM's stepped bore m/c's) no, zero, effect on brake bias. The type of linkage driving the m/c can, but not the m/c itself.
To me "off the shelf" kits are the demise of what hot rodding is really all about. I don't mind bought parts - I'm not that much of a curmudgeon, but a "bolt-on kit car" has nothing of value to me. You could probably tell that from looking at the Valiant's build thread...
We used an LBS on a 4WDB converted 4WD T-100 and I was very impressed by it. My Valiant came to me with a p-valve, so I used it (disc/drum), but long term I want to replace it with an LBS. Looks like BC Broncos sells the LBS for a little less than does the mfg that I linked above.
We used an LBS on a 4WDB converted 4WD T-100 and I was very impressed by it. My Valiant came to me with a p-valve, so I used it (disc/drum), but long term I want to replace it with an LBS. Looks like BC Broncos sells the LBS for a little less than does the mfg that I linked above.
txstang84
Well-Known Member
...I thought you said yourself, it doesn't adjust pressure? And parse the verbiage how you'd like, but by adjusting the so-called knee point in an adjustable P/V, it alters the rate at which rear brake pressure is applied in comparison to the front brake pressure. Again, it's not actually changing the pressure, but the rate at which it's applied based on either a fixed or progressive rate spring inside the p/v along with a shuttle valve.
I'll confess to not knowing much past the actual effects because I don't have a fluid dynamics degree and high school physics where we studied Pascal's, charles', and boyle's laws has been half my life ago, but I have witnessed roundy-round drivers altering their brake bias by either knob adjustable or multiple position P/Vs and the actual pressure measured at the line downstream of the p/v...they were different and dependent on brake effort.
And while I understand the m/c won't have a brake bias effect (minus notable exception of stepped bore diameters), that doesn't mean that an adjustable p/v won't have an effect on the application pressure at the caliper.
Perhaps there's something amidst this discussion I'm not capable of understanding, in regard to the actual science of it, but I know what I've see with my own eyes, and when I modified my '84 Mustang with 4 wheel discs...I had to remove the shuttle valve and spring from the factory fixed p/v and install an adjustable downstream to correctly modulate the rear caliper application under effort...which took some doing.
I will say this though, to the OP: there's a good chance if you're modifying the original drum/drum setup, or even a disc/drum setup, an adjustable wouldn't be a bad idea.
txstang84
Well-Known Member
That's all fine and dandy, but while I understand your perspective, not everyone sees it the same way. And while others' "bolt-on kit car"s have nothing of value to you, well...they're not your car, so...
Think about it this way...many folks want to have a cool old car and have an actual role in building the car the way they want and maybe they don't posses the same abilities as you...should they not be afforded the availability of better aftermarket parts which bolt on just because they aren't capable of the same level of fabrication? Or will you sneer down at someone because they didn't build their car from the ground up and use clever little workarounds from the island of misfit cars?
I'm sure there are a few folks who probably disapprove of your decision to retrofit a slant with the EFI from a GM 2.8 V6, but I don't see them raining on your parade either and saying you need to find the setup from a 3.9 V6 if you want to put it on a Mopar...I dig that you like to repurpose serviceable parts, but that doesn't mean you should see the work put into a "bolt-on kit car" as lacking value just because the parts were bought to fit and not modified.
txstang84
Well-Known Member
All that being said, I do admire the mods done to your Valiant
Woods74
Broke Senior
Most people don't want or can't take the time and liability to fiddle with fab, it takes a ton of time to produce something useful. To me, it's more personally rewarding than bolting on, but there is a trade off, you have to commit to it, and be into it. If I wasn't, it would be a different story.
Then there's that, 'is it more effective to buy something already made' factor.
Speaking from some one who built their car 'from the ground up'.
Some people get their personal reward in other things, maybe they wood work, maybe they play an instrument, maybe their an accountant. I have the same proud nature about my abilities, being a fab snob is like bragging about the size of your *****.... Cool story bro!
Back to the original question, take your ride out for a spin without any modification to about 30MPH, then slam on your brakes, if the backs lock before the front, you need an adjustable prop valve to dial it in.
Then there's that, 'is it more effective to buy something already made' factor.
Speaking from some one who built their car 'from the ground up'.
Some people get their personal reward in other things, maybe they wood work, maybe they play an instrument, maybe their an accountant. I have the same proud nature about my abilities, being a fab snob is like bragging about the size of your *****.... Cool story bro!
Back to the original question, take your ride out for a spin without any modification to about 30MPH, then slam on your brakes, if the backs lock before the front, you need an adjustable prop valve to dial it in.
I would like to thank all that took the time to reply. I thought I asked aquestion that would be a simple yes or no but boy was I wrong. After reading all the replies I now know that I have a lot more to mull over when it comes to the brakes on my Dart. Time to do more research.....
Again, THANKS.
DVO:banghead:
Again, THANKS.
DVO:banghead:
Try the Ram Man. he specializes in brakes and can tell you how and what you need. He probably has the right stuff that you need. He's a good guy and many people have said that they've learned alot from him.
7200 Winters St
Fort Worth, TX 76120
Telephone: 817.691.5996
http://www.theramman.com/
7200 Winters St
Fort Worth, TX 76120
Telephone: 817.691.5996
http://www.theramman.com/
2 Darts
A-body Addicted
What is a knee point? Can someone show me an illustration of what NTSQD is trying to say?
A four-wheel disk brake system on a Dart is an example of fabricating and fitting or off-the-shelf kit? I submit that any modification made to a vehicle that deviates from factory practice has elements of both. Sometimes I fabricate when what I need is not available at the time I need it. Sometimes I buy off-the-shelf not because I can't fabricate what I want but because someone else has made something better in appearance or function because I don't have the time, talent, tools, or materials to do better.
A four-wheel disk brake system on a Dart is an example of fabricating and fitting or off-the-shelf kit? I submit that any modification made to a vehicle that deviates from factory practice has elements of both. Sometimes I fabricate when what I need is not available at the time I need it. Sometimes I buy off-the-shelf not because I can't fabricate what I want but because someone else has made something better in appearance or function because I don't have the time, talent, tools, or materials to do better.
This particular graph is showing the different knee points for a valve with distinct lever positions rather than the slightly more common infinitely variable type. The adjustment in a p-valve is adjusting where the line changes from roughly 45° to about 30° It's not changing the pressure so much as changing at what pressure the pressure regulation ratio starts to happen. Essentially what it is changing is where in your pedal effort the reduction in rear pressure starts to happen. 1200 psi in brakes is pretty much panic stop mode.
I will venture a guess that the roundy-racers with a knob on the dash to adjust brake bias were not adjusting a p-valve. Could be, but unlikely. What they were likely adjusting was a Balance Bar brake pedal linkage working with two, parallel m/c - one for the front and another for the rear brakes. Like below. The knob on the dash is connected to the bar with a cable very similar to the core of a speedo cable. The bar is threaded and turning it moves the spherical bearing in the middle back and forth. The bearing lives inside a tube that is part of the brake pedal itself. Moving the bearing favors the m/c that it is moved towards. Needing/wanting more front bias (less rear lock-up tendency) means moving the bearing towards the m/c for the front brakes. In spite of how simple they look, they are not easy to set up and get right. Bill Wood ("wil wood") once commented to me that if it were solely up to him they wouldn't even sell them because of how much time his CSR's have to spend on the phone straightening out a mess that someone has made with one of them.
I'm not going to fab a V8 intake manifold, cost/benefit doesn't pay off, but I'd rather build a cable throttle system than try to make Lokar's excellent kit work the way that I want it to.
I don't sneer at anyone's car, I have too much respect for others to do that. I just don't pay much attention to one that is assembled from a bunch of kits w/o the time being taken to integrate those kits into one, cohesive car. Now when someone takes the time to make kit parts look & fit like OE, that really gets me going. Testing my wife's patience I'll probably try to find every little, subtle mod made to such a car.
I also don't have much brand loyalty. Used to be a Ford guy, and still am to some degree. This Valiant of mine is cool, I like it but I have no qualms about using parts from/for other brands if I deem them worth using. Same is true for all of my vehicles. My old ACVW dune buggy had a Toyota Electronic Ignition system adapted to it and it's shifter knob was from a Pinto Station Wagon. My FJ-60 has a Chevy TPI engine & 700R4 trans in it. The Early Bronco that I'm considering buying will very likely get a GM diesel engine (because a Cummins doesn't fit very well).
I will venture a guess that the roundy-racers with a knob on the dash to adjust brake bias were not adjusting a p-valve. Could be, but unlikely. What they were likely adjusting was a Balance Bar brake pedal linkage working with two, parallel m/c - one for the front and another for the rear brakes. Like below. The knob on the dash is connected to the bar with a cable very similar to the core of a speedo cable. The bar is threaded and turning it moves the spherical bearing in the middle back and forth. The bearing lives inside a tube that is part of the brake pedal itself. Moving the bearing favors the m/c that it is moved towards. Needing/wanting more front bias (less rear lock-up tendency) means moving the bearing towards the m/c for the front brakes. In spite of how simple they look, they are not easy to set up and get right. Bill Wood ("wil wood") once commented to me that if it were solely up to him they wouldn't even sell them because of how much time his CSR's have to spend on the phone straightening out a mess that someone has made with one of them.
I'm not going to fab a V8 intake manifold, cost/benefit doesn't pay off, but I'd rather build a cable throttle system than try to make Lokar's excellent kit work the way that I want it to.
I don't sneer at anyone's car, I have too much respect for others to do that. I just don't pay much attention to one that is assembled from a bunch of kits w/o the time being taken to integrate those kits into one, cohesive car. Now when someone takes the time to make kit parts look & fit like OE, that really gets me going. Testing my wife's patience I'll probably try to find every little, subtle mod made to such a car.
I also don't have much brand loyalty. Used to be a Ford guy, and still am to some degree. This Valiant of mine is cool, I like it but I have no qualms about using parts from/for other brands if I deem them worth using. Same is true for all of my vehicles. My old ACVW dune buggy had a Toyota Electronic Ignition system adapted to it and it's shifter knob was from a Pinto Station Wagon. My FJ-60 has a Chevy TPI engine & 700R4 trans in it. The Early Bronco that I'm considering buying will very likely get a GM diesel engine (because a Cummins doesn't fit very well).
2 Darts
A-body Addicted
NTSQD: Thanks for clarifying. Knee point is on the graph based on proportioning valve position and not the use of my leg. I had never heard the expression before.
DVO: I'm with Bill Grissom on this one. If you need an adjustable proportioning valve to get the front brakes to lock up just before the rears, so be it.
DVO: I'm with Bill Grissom on this one. If you need an adjustable proportioning valve to get the front brakes to lock up just before the rears, so be it.
nm9stheham
Well-Known Member
One important thing that is getting missed with adjustable p-valves : once you get the pressure pastt the knee point in the half of the system where the adjustable P-valve is located (front or rear), then the F/R brake bias varies with actual brake pressure. This can be OK in some applications where the braking effort is pretty consistent (like running circle track races), but can be bad where the brake pressure used varies quite a bit. This is usually the case on the street where you vary from grannie-smooth braking to panic stops.
For example, if the fronts were really weak, and you put an adjustable P-valve in the rears and put the knee to a low level to avoid rear lock up on dry pavement, then in even just a moderately hard stop on a wet turn, you will have issues with the fronts doing all the brkaing work and locking up and you will lose steering control.
This WILL really happen; if you drive your rod in the dry only, you may never see this. I have raced with these in rallies on all types for dry and wet pavement and dry and wet gravel, dirt, sand, and snow. They really can mess up the brake balance in variable brake force driving....which is what you have on the street.
IMO, adjustable P valves are not good for general street use, regardless of the lower cost. Other methods of adjusting brake bias like balance bars, adjusting friction material coefficients of friction, or changing MC's do not have this problem of varying brake bias with pedal pressure. So just keep that in mind when you consider using one....
For example, if the fronts were really weak, and you put an adjustable P-valve in the rears and put the knee to a low level to avoid rear lock up on dry pavement, then in even just a moderately hard stop on a wet turn, you will have issues with the fronts doing all the brkaing work and locking up and you will lose steering control.
This WILL really happen; if you drive your rod in the dry only, you may never see this. I have raced with these in rallies on all types for dry and wet pavement and dry and wet gravel, dirt, sand, and snow. They really can mess up the brake balance in variable brake force driving....which is what you have on the street.
IMO, adjustable P valves are not good for general street use, regardless of the lower cost. Other methods of adjusting brake bias like balance bars, adjusting friction material coefficients of friction, or changing MC's do not have this problem of varying brake bias with pedal pressure. So just keep that in mind when you consider using one....
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