Technical Help with Brake Combination Valve Question

Hi, I just recently replaced my booster in my 50 Ford shoebox with a Tuff Stuff 2222NA and I'm not sure what was in there before but it has a universal 7" underfloor booster/master setup. It appears to have a combination valve as well. The front is disc and the rear is drum.

I have it on jackstands in the front and tires on the ground in the rear. When I tested my booster install without the engine running and the pedal is pressed, when I let off I can feel way more resistance than with the pedal not pressed in. Does anyone know if I have an issue that requires adjusting the proportioning in this setup? I'm not even sure if it can be adjusted? I also thought maybe its doing this because more of the weight is on the rear with it on jackstands in the front. It seems to lock the front wheels ok when the engine is running but I wanted to verify my setup is sound with just manual brakes as well.

Also I have a small leak where the 3/8 fitting goes into the wilwood 10 psi residual valve going to the rear. It's a small drop but I'll have to replace it as the fitting is bottoming out. The 2 psi residual going to the front is totally dry.

I'm thinking to jack the rear up so its on all four stands, replace the wilwood valve and then replace all the brake fluid and bleed. It will suck as I'll have to figure out how the access in the floor was put together including taking carpet out.

 

You need to fix the leak first, and second, why are you only using one of the front port's? One port is supposed to go to each side on the front. One port per caliper.

 

I dont know much about proportioning valves but isn't there a safety thing inside which blocks off a failed side and needs to be somehow reset? Might explain your seemingly inoperative brakes? Info will probably follow here or is available from ECI for example. Edit, search YouTube gm proportioning valve reset.

Chris

 

What he said. People refer to them as proportioning valves but they aren’t. What they actually do is if there’s a leak in one of the circuits they block that circuit and illuminate the check light. The only “adjustment” is sometimes you need to reset the shuttle if you’ve had a leak, in which case the warning switch will trigger.

Get the leak sorted first, if there’s a leak there’s air. On top of that you probably can’t put enough force through the pedal with the pipe when the engine is off. I’d try it with someone actually pressing the pedal and then see whether there’s something to worry about.

 

You don't need to use both combo valve front ports, as long as the line splits further forward, like a stock shoe box does.

 

SDrocker, I know you don't want to see this, but the best thing to do is get rid of that damm combination valve, keep the residuals, and add an adjustable proportioning valve to the rears.

Do you know what kind of master cylinder you have, and if it's plumbed correctly?

Fix all the leaks, re-bleed, pressure test, check for leaks, then trouble shoot.

A dual master is under the floor of my '51 and can be serviced/bled from under the car without above access. Maybe not the easiest, but it can be done!

 

Yep. Unless every single component in your car's brake system is original to that combo valve, there is no way that combo valve is correct for your mixed breed system. Ditch it and put in an adjustable proportioning valve.
There is a ton of OEM engineering in that combo valve accounting for brake components, vehicle weight. front to rear weight bias, tire size etc, etc. None of that engineering works when the combo valve is installed in a different vehicle.

 

Yes, the shuttle valve can be your issue. To test it use the little wire wrapped around the unit and see if it's grounded. If it is you only have fluid passing through one half of the valve. And I agree, you don't need anything to do with the Big Brass manifold. They are just a big PITA! There sole purpose is to turn on the Idiot light in the dash and for Hot Rod guys a guaranteed place for leaks and dirty words.

 

Thanks, I'll leave the line going to the front port as is for now and fix the leak and re-check. This car did actually stop pretty well when I drove it around the block earlier in the year. I heard the hiss noise and changed out the booster and am seeing the leak now.

 

Thanks, I will fix the leak first and see where its at. When I drove it before it stopped pretty well. I just heard the hissing noise when pressing the pedal and decided to replace the booster and then saw the leak.

 

Thanks, pretty much how its set up right now. I'll fix the leak with the wilwood 10 psi connection and replace all brake fluid while I'm at it and bleed, recheck.

 

Thanks, I will fix the leak, rebleed, and check again and troubleshoot. The master is so close to the floor I have to access the opening they made and remove carpet and work from there, unless I take the master off the booster, set it on blocks so its a little lower and use some type of tool to push the piston in.

I'm not sure what type of master I have, nor if its plumbed correctly but it looks like it came from a 7 inch dual diaphragm booster/master combo kit that brings the combination valve. Mine looks very similar to this one:

https://westernchassis.com/1949-51-Mercury-Power-Brake-Conversion/

 

Thanks but how come I see these in the universal hot rod/customs sites? I see the booster/master and that same valve commonly offered as a universal kit. Is that intended for anything specific? I think I've seen somewhere this kit is sold for the 49-51 shoebox as well.

I think I have this one or something similar.. minus now I have a Tuff Stuff universal 7" booster I put in.

https://westernchassis.com/1949-51-Mercury-Power-Brake-Conversion/

 

You gotta have the car running to get the booster to operate and engage the master. I will add that I had a TERRIBLE struggle getting the (all new) 4 wheel disks on my '52 DeSoto to work properly. I finally went to a manual adjusted proportioning valve, a 7/8" diameter master to get enough pressure to operate the rear disks. It was frustrating, and expensive.

 

Thanks, I'm a little confused. The shuttle valve's black wire wrapped around one of the lines (as shown in my photo) is supposed to have a voltage on it when referenced to ground and I assume I check this with the key on?

I'm not sure why the brass manifold is included in the universal booster/master cylinder hotrod/customs kits

for instance this one:
https://westernchassis.com/1949-51-Mercury-Power-Brake-Conversion/

 

Thanks, yea totally! When I run the engine I can get the brakes to engage easily... what I'm worried about is the manual brakes not working if the engine is off and the booster has no vacuum in it (say a failed check valve or vacuum having been used up from a few pedal pushes). Although this may be a rare situation I don't want to find out the hard way later if something wasn't set up correctly. Shouldn't this still stop somewhat decently in that condition?

 

I know I’m going to regret this….

there are three different valves inside the combination valve, the pressure differential valve which only turns on the light, it does not block flow at all, I know someone will argue this so please show me factory documentation that it does….

Second is the proportioning valve. Prevents the rear drums from locking up due to the self energizing feature of drum brakes.

Third is the metering valve which blocks pressure to the front discs to give the rear shoes a chance to come off the anchor.

 

I read similar in the ebay listing for some of these universal master/booster kits that bring the combination valve.

I'm not sure if there's a better way (after fixing the leak) to make sure the fronts engage well other than having someone step on the pedal.

 

The shuttle valve has probably closed off the circuit with the drip or if you bled the system too aggressively. Take an ohm meter and touch one lead to the post in the center of the white insulator where the connector plugs in and the other lead to the valve body, if you have continuity then the valve has closed off one half of the brakes. Resetting them is not something I have ever done and I'm not even aware if that is possible. Another thing is that even though they all look the same, the internal calibrations are different depending on type of brakes, vehicle weight bias and other variable. The ones included on all of these kits are a mystery in their application origins. Here is a quick overview of how they work

https://mpbrakes.com/how-to-series-what-is-a-combination-valve/

 

Some of the brake component suppliers know little about the products they sell, and some others simply sell the same stuff to stay competitive. As jaw22w stated above, many hours are spent testing factory combination valves that can include proportioning, pressure differential (the light switch) and front disc metering (hold-off), all for specific vehicles, platforms and/or particular engineering requirements. (I know first hand) Sadly, many buy for looks, thinking more brake related stuff is cool! Much better to keep any custom brake system simple.

 

As 57 Fargo said, the differential valve's only purpose is to operate a lamp to tell you if there is a leak in one system. It doesn't block anything off. Your test of the front brakes doesn't mean much. You need to apply a lot of pressure to the pedal with the engine off to lock up the front brakes, I mean a LOT of pressure. Start the engine and the pressure needed is much, much lower.

 

Yea that makes sense, I'll see if I can find a helper at some point. For sure with the engine on its easy to engage the front with minimal effort.

 

I hate to admit this, but after having worked on cars, lots of brakes, since '60 I'm still unsure about this. Lots of info stating both 'they block/they don't block', on the 'net.

Case in point, in this thread there are two respected members in the 'don't block' camp.
Also in this thread is a link to a brake supplier, also well-known and respected with a video claiming they do block.

https://mpbrakes.com/how-to-series-what-is-a-combination-valve/

My educated guess is that some do and some don't, depending on original specs from the manufacturer and or OEM purchaser.

Does anyone have documentation that would support or refute that guess?

And, most important how are we supposed to tell which is which?

I'd like to believe that the seller, like the above link, know how their product works, but marketing and sales can 'improve' info on occassion.

 

My question to those who say they block a circuit is why do we have tandem master cylinders. The reason they were mandated for ‘68 was safety, to prevent a total brake failure. IF the pressure differential valve blocked the failed side there would be no need for them.
Read this….
https://www.jalopyjournal.com/forum/threads/tech-week-57-fargos-brakes-101.1229211/

 

This brake stuff is an ongoing issue here on the HAMB and why I generally "Do Not" even reply. Do a search and you'll find Hundreds of these posts. I only know what seems to work for me and I'm no engineer. If your switch only has 1 wire on it, it sure don't have any power applied ever. Once the shuttle valve slides one way or the other the switch goes to "Ground" and turns on the Idiot light.
All aftermarket Co's sell stuff to make $$$$ and seem to do it well. Once installed and the consumer has any kind of negative issue with their product, they always turn your problem to something You used, or You installed Wrong. They will never stand good for their product. Buyer Beware!!
Brakes are not all that complicated once you totally understand what you have and what you need. My best advice is to Not try to hand build something that has already been done by someone smarter than yourself. If you're going to change up brakes, then change up a total system not mix up stuff and think it's going to be simple.
Now, I know that is only my opinion and doesn't help you much at all. Sorry about that. That said I'm out. By the way, My avatar has GM disc on the front, 9" Ford in the rear, Booster and Master under the floor. No brass valve at all and stops amazingly nice.

 

That's a very good question, unfortunately you won't get any good answers. If you ask the aftermarket suppliers, they'll tell you need it but if pressed for details as to why, all you'll get is technobabble. The OEMs have dozens if not hundreds of individual part numbers for these, all supposedly calibrated for specific applications. The aftermarket sells precisely three versions: a drum/drum, a disc/drum and a disc/disc. The chances of this 'generic' calibration being correct for your application are pretty much nil. A cynical guy would say it's just a way to squeeze more money out of you.

The shuttle valve for the warning light is useless unless you're planning on installing a light. @57Fargo is mostly correct in that these generally don't 'seal' an open circuit, although I did run into one where that wasn't true. It was an oddball AMC drum/drum system that had an additional twist in that it wasn't resettable and sealed one of the front ports only. I pried that info out of a dealer tech. As the valve was NLA, I completely removed it and the brakes worked just fine...

That leaves the 'metering' valve. Although it would be better described as a 'delay' valve, as it does delay the front brake application to allow the rears to apply first. This is the only part that has any legitimate purpose for our purposes, but is it really needed? Prior to '67 and the requirement for a split system, these weren't present in the single-pot brake circuits and there were few complaints with either all drum systems or disc/drums. This can actually be addressed in the master cylinder by using a two-piece piston in a split master. GM makes these for a few applications (but you'll have to do your own research for those). Jaguar did this for years on their 4 wheel disc systems, all the way up to 1990 when they switched to ABS brakes. They never used one of these valves.

Last, the stand-alone rear brake proportioning valve. If you really press the suppliers about the combo valve, their default is to tell you that at least you need one of these. Or do you? If you're racing and trying to eke every last bit of performance out of the brakes, maybe. On a street car? I personally don't think so unless a need is shown. Remember, all your trying to do here is prevent the rear brakes from locking up before the front brakes so the vehicle won't swap ends in a hard stop. These valves reduce pressure to the rear brakes for tuning. I'd do a test drive first, only then would I install one if the rear brakes lock first. I've installed two of these, I ended up running both wide-open. The second one I took out, no difference in braking.

 

Oh ok thanks I see what you mean about the valve/ground. I agree with the other things you wrote. I'm basically trying to make whatever I inherited from the previous owner work.

 

Thanks for the really detailed response and insight! That all makes sense. I also had a 53 Chevy with disc in the front and drum in the rear and a 10 psi residual valve to rear and 2 psi to front.. all manual and it stopped well. I didn't feel it needed a residual valve but never tested it by trying to lock up the brakes.

I'm a little nervous about testing and seeing if I can lock up the rears first. I would need to try that in a big open parking lot perhaps and I'm guessing it would be easy to tell which locked up first?

 

Open parking lot or maybe an extra-wide street in an industrial area on a weekend. Having an observer along wouldn't hurt. If the front locks first, the rear of the car will want to come around so keep your wits sharp. Start at slower speeds (30-40 MPH) and work your way up. There's a lot of variables here; relative front/rear brake sizes, tire sizes, vehicle weight balance, etc, etc...