Proportioning Valve

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CluelessMopar

CluelessMopar

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I recently went to bbp disc brakes on the front of my 69 Dart. I ordered 74 Dart brakes from Rock Auto and new master cylinder for disc front/drum rear. I bled the brakes and had no leaks at the bleeders. Everything seemed good up til actually testing the brakes on a little brake check up/down my driveway. The brakes feel very very weak and sluggish. I have to drive my foot straight into the floor in order for them to fully engage. After a little inspection I noticed there was some brake fluid on the proportioning valve. This would be the stock proportioning valve for small bolt drums all around. Is there another proportioning valve I should be using? Should I drive the car a bit for a brakes/calipers to break in? Any thoughts on why they might be sluggish.

IMG_20211204_213930_407.jpg
 
Do you know if you have 2 distribution blocks now? The main and then a smaller one about a foot back.
 
If you had 4 wheel drums you had/have a DISTRIBUTION block, not a proportioning valve...
 
I cannot tell from your photo, do you have the calipers installed so that the brake line and bleeder are 'at top?' Do you have a good hard pedal? Or does it go down "all the way" (or most the way?)

With no proportioning valve, normally "one end" of the car will lock up way before the other, a prop valve has nothing to do with whether it "stops at all" or how hard you push or how far the pedal goes.

You can buy aftermarket adjustable valves, and add them into the system, leaving the original distribution block/ warning switch in place
 
disc/drum is gonna apply 70+% bias to the fronts and IIRC they apply the rears a little first then the fronts? Go with the disk/drum prop valve. The disk calipers take much more fluid displacement than the rear drums (hence the larger reservoirs) so if they are all 4 being equal, your not going to get the correct biasing.
 
You may have several problems, so don't lose hope.
The lack of a Proportioning valve, like Del says is Not your biggest problem at this time. I have no P-valve on my combo, but I do have 295/50-15 tires on the back with very small wheel cylinders.
If you have four same-sized tires on your car, you will have to get some kind of reduction-system in the rear lines, no matter what, or suffer spin-outs on a regular basis with heavy brake application.
But that is not your current problem.
You have two or three current problems;
1) the low pedal and
2) the high required pressure, and
3) probably a spongy pedal.
4) and possibly you may not be aware that disc brakes are NOT self-energizing like the drum brakes were, so will require a great deal more leg power, unless you have installed a power booster.

Ok so lets look at these one by one;
but first, a few questions;
1) Do you have a booster?
2) did you bench-bleed the master?
3) To which end of the car, did you plumb the front reservoir?
4) What is the size of the master cylinder bore?
5) why did you install the calipers to the front?
6) are the calipers actually free-floating?
7) and as already asked; are the bleeders at the highest points of the calipers?
8) does the pedal come up higher with multiple pumps?
9) do multiple pumps make the pedal harder?
for 8 and 9, you have to stroke faster than the fluid is able to return, but the pedal has to come all the way back up to the top each time.
10) with the system fully relaxed, have a helper slowly apply the brake pedal about one inch then allow the pedal to very slowly return to the top of it's stroke; while you are looking into the reservoirs with a flashlight.. You should see the fluid roiling from the Compensating ports, right during the top inch of pedal travel in BOTH directions.
BE WARNED;
If your helper pushes more than an inch AND if there is air in the system, then it is possible to get a fountain on the upstroke as the fluid returns to the reservoir. I have seen gusher-fountains erupt and hit the underside of the hood. Brake fluid is not paint friendly, so if this happens to you, you gotta have the cleaning supplies, including some Brakleen, right there. I will not buy you a new paintjob..
This test is very important to proving that your M/C pushrod is properly engaged and adjusted to the correct length.
 
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Like Wayne stated, stock 4 wheel drum cars use what is actually a distribution block that has no proportioning function to it.
4 wheel drum cars, as well as cars fitted with 4 wheel discs, need NO proportioning valve. The drum cars rely on wheel cylinder sizing to establish the brake proportioning bias. Same applies to the 4 wheel disc systems.
Front disc/rear drum cars DO need some manner of proportioning so that each end of the car gets the proper line pressure. Wheel cylinders require much less pressure from the master cylinder to energize. Disc brake calipers are much bigger and require more pressure and fluid volume to operate. The factory 4 wheel drum distribution block looks like this:

D D D valve.JPG


The proportioning valve looks like this:

XH 505.jpg
 
I opted for an adjustable proportioning valve when converting to front drums. Really allowed me to dial in my front/ rear braking bias.

Be well,
Pat
 
Kern Dog said:
Like Wayne stated, stock 4 wheel drum cars use what is actually a distribution block that has no proportioning function to it.
4 wheel drum cars, as well as cars fitted with 4 wheel discs, need NO proportioning valve. The drum cars rely on wheel cylinder sizing to establish the brake proportioning bias. Same applies to the 4 wheel disc systems.
Front disc/rear drum cars DO need some manner of proportioning so that each end of the car gets the proper line pressure. Wheel cylinders require much less pressure from the master cylinder to energize. Disc brake calipers are much bigger and require more pressure and fluid volume to operate. The factory 4 wheel drum distribution block looks like this:

View attachment 1715836098

The proportioning valve looks like this:

View attachment 1715836099
Click to expand...


I'm not trying to hijack the thread but here goes as this may be related to the OP's question: I had a front disc brake conversion done on my '68 Dart and the brakes seemed OK for a while, the guy who did the swap pulled my Distribution Block and plumbed in an aftermarket adjustable Proportioning Valve (which started leaking almost immediately). I recently bought a new Disc/Drum correct master cylinder so I can go back to the Dist Block setup and get my dummy switch working again. The new mechanic installed it for me and plumbed the old Dist Block back in (I'd love to see a plumbing diagram for the original Dist Block if anyone has one???). The swap went fine and the front seemed to work well but the rears just won't grab to lock up when idling in gear on the hoist? There seems to be a little sigh/hiss/wheeze from the brake master after it first is depressed. So that leads to 2 questions:
1) Is there some sort of plumbing issue with the Distribution Block and can I get a plumbing map to make sure we have the lines in correctly?
2) What is the correct Brake Booster for my application? Does Summit Racing have a part number for one which is correct for my vehicle (1968 Dodge Dart convertible had a 273 before the engine swap)? I'm in Canada so Summit.seems to be the only Mopar shop up here.

Hopefully my problem is parallel to the OP's and our problems overlap a little so the answers will help everyone!

Thanks in advance.
 
67Dart273 said:
You really need to start your own thread. When you get two questions going in one thread it really confuses the issue
Click to expand...


Fair point. I sort of thought the OP and I had a fairly similar problem and I wondered if maybe the diagnostics might not apply to both of us and solve two birds with one stone. I suppose the question about the plumbing connections on the distribution block might be worthy of its own post.
 
A lot of good advice here, would like to add a little myself. Yes, new brake pads need to be broken in, but you also may have another problem besides what was already stated. Did you replace the rear flex hose at the rearend. It could be collapsed, that can not be seen from the outside. Inexpensive fix.
 
Good advice mainly.

There are two styles in A's with Factory Disc/Drum Brakes!

In 1969 the style used for Disc/Drum was a separate hold off "Texas" valve about 10" down the frame rail from the main distribution valve.

In 1973 it was combined in with the distribution valve! "Combo Valve"!

First I would make sure my Bleeder valve on the caliper is always to the top! Old Hoses and line can be an issue as well as any other brake components!

Examples of 67-72 and 73 up valves! BB cars need the heat shield so swapping a 73 up in the earlier BB cars does not work to well as the bolt up is not the same! JMO!

IMGP1740.JPG


IMGP1741.JPG


IMGP1561.JPG
 
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