Anyone ever eliminate the prop valve?

-
Kern Dog

Kern Dog

Build your car to handle.
FABO Gold Member
Joined
May 23, 2010
Messages
9,749
Reaction score
28,042
Location
Granite Bay CA
I've had trouble for months trying to get my brakes right, and I'm considering eliminating the brake combination valve. I'm thinking of plumbing the master to the wheels directly by running the front M/C reservior to a TEE, which will run to each front wheel. For the rear, I might run a line to an adjustable proportioning valve, which will then just run to the axle and split from there.
Has anyone out there made this change to their cars?
 
Allright, FIRST what are we workin' on?

And ARE YOU SURE that "the valve" you have now is ACTUALLY a proportioning valve?

(IE---is this a drum to disk conversion?)

Read this, maybe you simply have a drum warning light switch?

http://www.forabodiesonly.com/mopar/showthread.php?t=134889

There is no reason, if your valve is truely a troublesome prop valve, that you can't remove it and run a separate valve ---BUT

if it is an integral valve like this

c3tk8.jpg


you might not have to fiddle with extra tees. You can just gut the prop valve section (on the lower right of the diagram) and use what's left for a distro block, and simply add your aftermarket valve downstream
 
Frankenduster said:
I've had trouble for months trying to get my brakes right, and I'm considering eliminating the brake combination valve. I'm thinking of plumbing the master to the wheels directly by running the front M/C reservior to a TEE, which will run to each front wheel. For the rear, I might run a line to an adjustable proportioning valve, which will then just run to the axle and split from there.
Has anyone out there made this change to their cars?
Click to expand...

That's exactly what I am running on my manual 4 wheel disk brake car.
It's what the tech guy recommended from master power brakes.
 
That's what I'm running too with 11.75" discs in front and 11x2.5" drums out back. I plumbed the prop valve so it emeges through the floor between the drivers seat and the rocker... I can adjust it on the fly. I use a 2 lb. (maybe 10, I can't remember) inline residual valve just behind the prop valve.
 
Many have done exactly what you suggest. I did so on my 65 Dart and am working on that for my 64 Valiant. I used a later aluminum MC on both (w/ booster on Dart).

You may need to leave the T hanging, just supported by the tubes. Another option is to get the distribution block from a pre-68 car (like mine) and plug the R port to make a front T (as I did). However, why not just take out the guts of your proportioning valve per 67Dart273's photo above (spring and plug), then use your external adjustable valve. That will leave your warning switch. If so, you might want to mount it high so the prop valve is not down in the mud.
 
Some interesting and helpful replies!
I'm not interested in a brake warning switch or the light. When the pedal softens up, thats enough warning for me.
The car is actually a 70 Charger. I have posted about my brake problems on several forums, but THIS is the only time I have seen anyone address the issue of modifying the combination/proportion valve. This is a great idea since I have a few spares to work with.
The specs: 12" Cordoba discs, 2.75 piston iron calipers spec'd for an 81 Diplomat. 10.7" rear disc kit from Dr Diff. Rear calipers have 1.5" pistons. 15/16" aluminum NON power disc/disc master cylinder with a drum/drum combo valve. Prior to Feb of this year, I had a power booster with a disc/drum master from a 75 Dart. I only changed to manual because my low idle vacuum made slow speed stops difficult.
The pedal feel is great: it gets firmer the closer it gets to the floor. Its just that the feel of the pedal isn't equal to what happens at the calipers. I cant get the front tires to skid at all. I had to stand on the pedal to get the rears to skid. I have always believed that the brakes are the most effective the moment BEFORE they lock up. If i can't get them to lock, I MUST have a "low pressure" situation, at least at the front. I've considered buying a guage to test the pressure at the caliper, but I'd also need to know what the pressure SHOULD be.
I might try these mods to the combo valve. The price is right!

Okay... with the proportioning spring removed, would this mean that the front AND rear would then get equal pressure? What happens with the vertical sliding "barbell" that sits between the front and rear chambers? Does that stay in place? I would think so, since without it, it could be a step back to the 'pre 1967 ONE pot theory.

I appreciate any and all suggestions. I'm just about ready to put the power brakes back on!
 
Yes, this thing is two separate functional devices "in one box." In the drawing, the piston on the left side (of your device) is the shuttle which actuates the warning switch, and you don't want to remove that, as it would then CONNECT the front/ rear hydraulic paths

The "bottom right" section of the valve, in the drawing of your device, is the proportioning section. If you look at a (for example) 67 all drum warning switch (pictured below) with NO proportioning valve, you can see the "switch only" and how it works, and that it is essentially, "half" of the newer combination switch/ prop valve
 

Attachments

  • 67switch.jpg
    93 KB · Views: 2,406
Pedal ratio... yes!
Feets also responded to a few of my posts. I use the same screen name there as I do here. The issue of pedal ratio is a little murky.
I measured the Charger and an A body setup. Using the following math, I came up with a 6.6 ratio for the Charger and 6.92 for the A body.
CENTER of brake pedal pad to center of its pivot/mount: Charger 12 3/8"
CENTER of brake pushrod to to center of pivot: Charger 1 7/8"
Thats 6.6 to one
The A body was 11 1/4" and 1 5/8", resulting in 6.92 to one.


On the subject of prop valves: I gutted a disc/drum and a drum/drum prop valve last hour. I expected to find that by removing the guts of the warning switch, I'd be connecting the front and rear ports. I blew compressed air through and found that they were STILL seperate, OR the insides are so gunked up that the passage is blocked!
 
A few more nuggets:
The car currently has a drum/drum combo valve, UNmodified.
Pedal ratio COULD play a role. The pedal in the car is the same one it had in December 1969. The manual disc setup MAY have been doomed from the start. Heres why: The car originally has 4 wheel drum brakes. Drum brakes require LESS fluid volume and pressure. It stopped okay with the original setup. I switched to power disc/drums. It stopped great at all speeds. I added rear disc brakes because I thought that they would look better through the wheel spokes. The braking barely improved. Later, as I tuned the motor and got it to idle down to 700 in gear, the low vacuum made slow speed braking pretty bad. THAT is why I went to a manual master cylinder.
The POINT ??
The pedal ratio MAY be fine with the A body power brake booster and M/C.
The pedal ratio was fine with 4 wheel drums since they require less force.
Maybe the pedal ratio simply is NOT enough for the 4 wheel manual discs.
 
Perhaps using a prop valve from a disc set up might make the system work right. The prop valves for disc and drum are different and im sure there is a reason
 
Pedal ratio is essentially the same effect as cylinder bore

That is, if you use a pedal with a shorter actuator arm/ longer pedal arm, you'll have more foot movement, and more brake pressure.

Be careful though, that you have enough to fully actuate the master before you hit the floor (lost stroke)

Same thing is true of bore

Smaller bore means more foot pedal movement, but higher brake pressure

Both of these obviously can only go so far--as you may run out of enough volume of fluid to actuate the brakes before hitting the floor!!
 
After bleeding the system, the pedal is high enough that it never touches the floor.
 
Thanks for the help guys. I ended up pulling the manual master and put the old stuff back on.
I just got tired of fighting everything. I'll probably add a vacuum pump to crutch the low vacuum at idle.
 
You must log in or register to reply here.
-

Back
Top