Proportioning valve

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44067gtdart

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Is the proportioning valve a direct replacement for the distribution block on a 1971 Dodge Dart Swinger? Will I need to use adapters or buy new lines? I did switch to a proportioning valve on my 67 Dart, and I believe everything bolted up without any modifications.
 
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I say... Can't tell with out knowing what "proportioning" you are referring to.

In 67 there was a proportioning valve and a seperate distro block. Some where in the later years they replaced the 2 seperate parts with a combo unit.
 
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I say... Can't tell with out knowing what "proportioning" you are referring to.

In 67 there was a proportioning valve and a seperate distro block. Some where in the later years they replaced the 2 seperate parts with a combo unit.
Car now has 4 wheel drum brakes. Upgrading to Kelsey Hayes front disc brakes. Same thing I did with my 67 Dart. I believe I just took the distribution block out and bolted the proportioning valve in place. I just didn't know if the 71 was the same. On the 67 I believe I just had a distribution block.
 
Based on what Mattax posted, your car has the combo type valve so I would assume that you can just bolt in a 70 up combo valve
 
Based on what Mattax posted, your car has the combo type valve so I would assume that you can just bolt in a 70 up combo valve
Not with a drum brake car.
A factory disk equiped car built after Jan 1 would have come with the combo valve.
When converting the fronts to k-h fixed calipers use either
the original safety with a proprtioning valve in the rear line (as was done '67-69)
or
a combination valve.

Factory valving works well with matching factory rear brakes; or depending on shoe and pad linings, tires, pavement, etc., sometimes slightly smaller rear wheel cylinders.
 
A factory disk equiped car built after Jan 1 would have come with the combo valve
My reasoning was the 71 would have had a combo valve or a distro block but both would have the brake warning switch in it. If the OP has a post 70 combo valve I assume ( and we know what that means) if he had a drum / drum distro /brake warning block that the combo valve would be a bolt in.

Again it was an assumption that the factory would have used the same hard lines for either disk or drum to save money and the combo valve / distro block would have the same mounting and inlet / outlet locations would be the same.

I could be 100% wrong and they made them unique to prevent a distro block being put into a disk brake car.


I'm so confused!
 
You need to know WHY, you would need a P-valve(Proportioning) or a C-valve(Combination), and what the words really mean.
So first-off, the definitions;
A P-valve reduces the pressure to the rear brake cylinders to a percentage of whatever pressure is being sent to the front.
A C-valve is a P-valve with a safety switch incorporated into it, that can be used to turn on a light on your dash, to tell you that one end (either front or rear) of your system has suffered a pressure loss.
Now, the reason.
There is only one reason to run a valve like this, which is to prevent the rear brakes from locking up prior to the fronts. When the rear locks up first, at speed, the rear usually steps out from behind the fronts and quickly sends you into an irrecoverable spin.
With Drum/drum brakes,and four same-sized tires; the front brake shoes are wider than the front, making them do about 85% of the braking. Ergo, the system is balanced by the engineering of the total shoe contact area, and sometimes the the balance of the W/Cs gets involved.
But when you install disc brakes on the front only;
It requires way more pedal pressure to affect the same stopping power because the self-energizing feature of drum brakes is no longer helping, and of course, that, way more pressure is also fed to the rear. And so, the rear brakes have a tendency to lock up first under heavy braking...... with four same-sized tires. And so the P-valve was invented to help prevent that.
Now; if you have different sized tires from one end of the car to the other, then you will have different proportioning needs.
Hotrods usually have big fat rear tires, so the proportioning CAN be engineered to send more pressure to the rear for even better braking , in combination with the front discs.
On my car for instance, a 68 Barracuda;
On the front I have 235/60-14s, with the KH four piston calipers. and
On the rear I have 295/50-15s, with 10x2 shoes.
I found that I could run NO PROPORTIONING at all, AND, I changed the rear w/cs to one size bigger, for more brake-force on the rear. This was done by field-testing, to make sure the back of the car stayed in the back, under the most severe braking situations.
My rear shoes now wear out faster than my front pads.

If you are running four same-sized tires, in a disc/drum system, then you NEED a P-valve, period.
If you have a light on your dash to tell you that the parking brake is on, then you can use a C-valve, and connect it to the light.
The C-valve from a 73 up disc front brake A-body will work just fine. And if you don't want to wire up the Safety switch, then don't,lol.

There is only one over-arching caveat, namely, do not let the rear brakes lock up prior to the fronts, because; when the back steps out, you only have milliseconds to avoid a spin-out.

Ok I hope that helps.
 
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Is the proportioning valve a direct replacement for the distribution block on a 1971 Dodge Dart Swinger? Will I need to use adapters or buy new lines? I did switch to a proportioning valve on my 67 Dart, and I believe everything bolted up without any modifications.
Find the Ram Man site. Fort worth Texas has all ya need
 
P-valve(Proportioning) or a C-valve(Combination), and what the words really mean
I think we are getting into semantecs but...


There are 3 devices that our cars use from the factory.

1. Distribution block with a brake warning light in it. (Drum/drum)

2. A distribution block with a brake warning light, with an external proportioning valve. 67 to mid 70, probably earlier years as well. (Disk / drum)

3. A "combo" valve that has distribution block, brake warning light, and proportioning valve all in one. Mid 70 up, (disk / drum)


Your points about the rear locking too soon are spot on.
 
A P-valve reduces the pressure to the rear brake cylinders to a percentage of whatever pressure is being sent to the front.
Not quite.
They do nothing when the line pressure is moderate.
They proportionally reduce the increase in line pressure above the set point.
There is only one reason to run a valve like this, which is to prevent the rear brakes from locking up prior to the fronts
Yes its used with front disk-rear drum combinations to offset the amplification of braking force of the duo-servo drum system in the situations where heavy braking has shifted the weight to the front.

When the rear locks up first, at speed, the rear usually steps out from behind the fronts and quickly sends you into an irrecoverable spin.
That pretty much sums it up.
 
Again it was an assumption that the factory would have used the same hard lines for either disk or drum to save money and the combo valve / distro block would have the same mounting and inlet / outlet locations would be the same.
That's a logical theory.

For the OP, going from a 10" drum brake system to a K-H front, with the nominal 10 x 1.75 rear drum, changin to a combo valve very well may avoid having to change or modify the hydraulic hard lines.
 
That's a logical theory.

For the OP, going from a 10" drum brake system to a K-H front, with the nominal 10 x 1.75 rear drum, changin to a combo valve very well may avoid having to change or modify the hydraulic hard lines.
So what would be the correct combo valve to use? I definitely would like an easy bolt in swap.
 
Do you have four same sized tires on the car?
If yes then any valve off a disc/drum A-body will work.
You can fine tune it, if you need to, for your application with one of three sizes of rear wheel cylinders, or by the use of braking materials.

I started with a 73 disc/drum C-valve, and as my rear tires got progressively taller and wider, I eventually just gutted the proportioning part of the block.
 
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And what rear brakes?

What other changes?

Actually probably don't want answer this any more directly than I've indicated above.
If its stock, then following the factory setup will be the best bolt in all 'round performance.
The one thing that won't be quite the same is the lining materials (unless you buy old stock and that's got pros and cons). So that's one variable you'll still have to experiment a bit with.

For not quite stock, or specialized performance use (such as high speed track or circle racing on pavement or loose ) then it may be desireable to have an adjustable proportioning valve. Also another tuning variable that I mentioned earlier is very slightly smaller (or sometimes larger) wheel cylinders.
 
As already mentioned;
the aftermarket makes an adjustable one. This will grow with you if you foresee up-sizing the rear tires. You just plumb it into the rear line wherever it is convenient.
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ok, not that my brain has been totally abused from all the above, let me ask a simple question and hopefully i can understand the answer. My 72 dart swinger 318 had factory brake drums all around. (build sheet info) it came to me with disc. conversion with what appears to be 1973 disc brakes on front. they have been on the car for a l o n g time by the way they look. they look totally factory is what im trying to say. now, the block appears as old and factory also. so the question is: are the blocks the same for 72 drum as with the 73 disc? if not how do i know the difference. right now the brakes feel like the rear sets down first before the front as the rear drops before the nose dips. hope this explanes it ok.
 
ok, not that my brain has been totally abused from all the above, let me ask a simple question and hopefully i can understand the answer. My 72 dart swinger 318 had factory brake drums all around. (build sheet info) it came to me with disc. conversion with what appears to be 1973 disc brakes on front. they have been on the car for a l o n g time by the way they look. they look totally factory is what im trying to say. now, the block appears as old and factory also. so the question is: are the blocks the same for 72 drum as with the 73 disc? if not how do i know the difference. right now the brakes feel like the rear sets down first before the front as the rear drops before the nose dips. hope this explanes it ok.

I'd like to know this as well.

Do the mid 70 distribution block/brake warning switch look visibly different then the proportioning valve/brake warning switch?
 
I opted to go with an adjustable proportioning valve (Wilwood) when converting to front discs on my Duster. Works great and allowed me to really dial in the front-rear brake bias.

Pat
 
I'd like to know this as well.

Do the mid 70 distribution block/brake warning switch look visibly different then the proportioning valve/brake warning switch?

Ok, did some more digging. First picture is a drum/drum distribution valve with brake warning switch.

Second picture is a disc/drum proportioning valve with brake warning light switch.

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right now the brakes feel like the rear sets down first before the front as the rear drops before the nose dips. hope this explanes it ok.
It does explain it ok. What are the tire sizes?
Mine does the same, because
I set it up that way,because
my car has 295s in the back, and 235s in the front.
If I had same size tires on the rear, the rear tires could/would, lock up first. And if/when that happens, then there is no way to keep the back in the back, and it usually spins you out.
But with bigger tires in the back, it is nearly impossible, on my car, to lock the rears first, so it is as you say, like throwing a parachute out the back, as the rear seems to drop microseconds earlier.
I gutted my P-valve as a test, and when it worked like this, I left it like that, and swapped in different wheel cylinders for fine tuning.I like it, but it was a lil unnerving at first.
 
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