Proportioning valve

[1970Tex]

Hey guys, looking for some help sourcing a GOOD quality proportioning valve. 1970 half ton, 2WD, front disc conversion, manual (no booster).

Finally got my truck off the lift, and i thought i would be off to the alignment shop, but low and behold the brakes were extremely weak. Firm pedal but not much bite at all. Tried bleeding the brakes (with home made tool to keep P.V. shaft centered) and barely anything coming out the rears. Bench bled MC, tried again, still nothing. So i figured the P.V. must be stuck. From what i can read, you should be able to slide it one way or the other with a pick. After removing the P.V. assy from the truck and dismantling, the valve moves extremely stiff. Basically i need to force it with a punch to get it to move.

Ordered a new PV2 valve from Amazon, you know, the ones for $50 made in China and was lured in by 2 day delivery. Everything looked good until i installed it, and found out it leaks. Of course its the special 7/16-24 UNS threads for the rear input. It seems like they didn't tap it deep enough, but after inspecting farther, i measured .240" from the top of the valve body to the top of the flare on the new one, and my old one measures .208".

So I'm thinking with 2 P.V.s i should be able to transfer the piston from my new one, into the body of the old one...Nope. Won't slide at all.

I give up, ill call this a wash (and a good lesson). Where can i find a good proven possibly made in USA valve?

[ivory68]

I had the same symptoms, and I was close to buying a new distribution block. Tried to bleed the rears, and I barely got any fluid dripping out. I finally isolated it to the flex hose at the tee fitting above the axle. Turned out that it was completely blocked. Got a replacement hose from O'Reilly's. I really didn't want to replace my block, as it is a cast iron one that came with the ECE conversion kit.

[1970Tex]

I sort of Jerry rigged it with teflon tape just to prove it out, and i finally did get good flow finally out the rears, but teflon tape will eventually deteriorate over time with brake fluid.

[RichardJ]

The threads are not intended to do the sealing. If the taper isn't sealing then you should get a copper flare gasket.
Napa used to have them in some stores. I get mine from Grainger.
That image may be misleading. They're very useful for hydraulic brake and steering lines.


>>So i figured the P.V. must be stuck. From what i can read, you should be able to slide it one way or the other with a pick.<<

You have a COMBINATION VALVE. That assembly at the rear is the Proportion Valve. The rest of it IS NOT.
The middle of the Combination Valve is the Pressure Distribution Switch.
The valve at the front is a Metering Valve.

The Combination Valve has three completely separate and independent sections. Each has its own job.
The piston in the Pressure Differential Switch will have equal pressure on both ends, depending on how hard you push the brake pedal. You can have 100 psi on both ends or you can have 1500 psi on both ends. It will move when the pressures become unequal in either the front or the rear of the piston.

[PbFut]

I went through this a couple years ago. I found no us made. The expensive ones are just branded, painted or etched version of same part. With a good flair nut wrench, torque that baby down. Or as above find some conical washers. They are not easy to find in my area. Amazon or a good race shop like Pegasus will have them.

[1970Tex]

Yes i agree the threads do not do the sealing, its the seated flare that seals it. The threads just don't protrude deep enough into the body to allow the flare to contact. If i had a 7/16-24 UNS bottoming tap i would try to get another 1/4 turn out of it. I have been trying to source a flare gasket locally. and all i could find is a 3/8" (too big). I appreciate the Parker part #s, that is quite helpful!

PbFut...i have tried to make it very tight, and 1 it still leaks, and 2 when disassembled looking in the brass inlet port, there is no signs (metal distortion) the the flare is making contact. I think the flare gasket is the answer. As consumers we really need to demand better quality parts from our distributors. Id gladly pay 30% more for domestic quality components.

Also, RichardJ you are correct, it is a combination valve. Many parts outfitters refer to it as proportioning, it even is part marked "PV2"

While bleeding the brakes (with both old and new) i noticed if i step on the pedal hard and quick, i can hear and feel some clicking going on in the valve. This was with the switch terminal removed, and the centering tool installed. What exactly is occurring when this happens, and is it normal?

[RichardJ]

>>Many parts outfitters refer to it as proportioning, it even is part marked "PV2"<<
Many suppliers perpetuate the stupidity and are not helping anyone.

>>While bleeding the brakes (with both old and new) i noticed if i step on the pedal hard and quick, i can hear and feel some clicking going on in the valve. This was with the switch terminal removed, and the centering tool installed.<<

Pressure bleeders that you may buy/use operate on 10-15 psi. air pressure.
Vacuum bleeders that many use, operate on 20-25 hg of vacuum.

While manual bleeding, you may generate anywhere from 100 psi to 1000 psi, depending on how hard you push.
Say you have 500 psi on the MC output and into the CV ( combination valve). 500 to the rear line and 500 to the front line. Or, vise-versa, it doesn't matter.
You crack a front or rear valve to bleed some more air out. The pressure in the side you crack drops to near ZERO. The other side is still at 500 psi.

The nipple on that piece of ****tt centering tool - bleeding tool is history. It doesn't stand a chance against the 500 psi. That differential pressure slug is going to move.

I have watch a comedy show on TV called Roadkill Garage with David Freiburger and Steve Dulcich. I've seen two of their shows where they manually bled brakes using one of those centering tools. It breaks every time and they still haven't figured it out.


https://www.grainger.com/product/PAR...srrItems_5WRW1

https://www.grainger.com/product/PAR...srrItems_5WRW0

[LS short box]

I don't know if your truck is totally stock and you want to keep it looking that way.
On my hot rods I use Wilwood adj prop valves. Adjusts at the knob to adjust for rear brake bias.
My C10 is far from stock. Pic of the prop valve mounted below the master.

[70STOVEBOLT]

In the 1971 Chassis manual, it shows a special tool that just holds the button in on the front of the valve. Does that do the same thing, center the valve for bleeding?

[70STOVEBOLT]

Here is a pic of what I am talking about, circled in blue.

[RichardJ]

>>tool that just holds the button in on the front of the valve. Does that do the same thing, center the valve for bleeding?<<

NO. The two have absolutely nothing to do with each other.

The Metering Valve is closed below a pressure of about 75 psi. The tool in the image is used to hold the valve open to make it easier to bleed the front brakes.
That tool used on the earlier combination valve pushes the Metering valve pin IN.
A different tool is used on the later type Combination valve to hold the metering valve pin OUT.

[1970Tex]

RichardJ, thanks for the links on flare gaskets. I managed to get some from Amazon. I'm not too impressed with the local wholesaler here (who supplies to Napa and Piston Ring locally here), but the flare gaskets did solve my leaking problem.

LS Short box, beautiful job on your engine bay. I like how clean your firewall turned out! Mines mostly original still. One day hope to have it a little cleaner.

70Stovebolt, RichardJ can correct me if I'm wrong, but my understanding is without the tool installed, when you crack the bleeder open (say on the rears) WITHOUT the tool installed, it will sense loss of pressure and shut off fluid going to the rear, to preserve front braking. Vice versa also. It keeps the switch piston where it needs to be in order to properly bleed air out.

[franken]

There are also tools all over the internet that replace the switch in post 11 to keep things centered.
I'd think used parts people on the site have piles of the prop valves lying around...

[mr48chev]

That tool also keeps the tip of the switch from being broken off when the piston goes all the way to one side while bleeding the brakes.

[Accelo]

I had two Metering Valves leak and not from the fittings, #3 held.
Just crap is all I can say.
If it wasn't for crap I would not have been able to assemble my China Crap truck.
It only angers me because they can, and do, make better parts.
My conclusion is it's crap because we require cheap crap.

If GM still built them they would cost $300, not $50.

[70STOVEBOLT]

Originally Posted by RichardJ

>>tool that just holds the button in on the front of the valve. Does that do the same thing, center the valve for bleeding?<<

NO. The two have absolutely nothing to do with each other.

The Metering Valve is closed below a pressure of about 75 psi. The tool in the image is used to hold the valve open to make it easier to bleed the front brakes.
That tool used on the earlier combination valve pushes the Metering valve pin IN.
A different tool is used on the later type Combination valve to hold the metering valve pin OUT.

Just to be sure, as the chassis manual is a little vague: The pin needs to be held in while bleeding both the front and rear brakes, or only the front? I'm a little confused on what constitutes an "earlier" and "later" combination valve.

[Rust_never_sleeps]

Originally Posted by 70STOVEBOLT

Just to be sure, as the chassis manual is a little vague: The pin needs to be held in while bleeding both the front and rear brakes, or only the front? I'm a little confused on what constitutes an "earlier" and "later" combination valve.

Metering valve delays the front brakes(in a disk/drum setup) so propping it open makes it easier to bleed the fronts. The rear brakes won't care whether it's open or not

[RichardJ]

>>what constitutes an "earlier" and "later" combination valve.<<

Probably not a good choice of words on my part.
In the late 60's GM CARS with disc/drum brakes used three individual devices instead of a combination valve. The first image below shows a distribution block with switch, top left, Proportion valve, top right and Metering valve on the bottom. Combining the valves into one eliminated a number of fittings and potential leaks,

I don't know if the trucks ever used the individual valves. All I have ever seen were the cast iron combo valves of which there are at least two styes.
At some point, the cast iron valves were replaced with the flat machined brass valves and that is the type sold by the aftermarket. Most (maybe) of the flat style use a Metering Valve that needs the PIN pulled OUT when bleeding. There are a couple of different tools available to pull and hold the pin.

Post #10 above, shows a cast iron combo valve with a tool that holds the metering Valve Pin IN.

https://www.google.com/search?q=how+...GLXITkD2Y,st:0


>>The pin needs to be held in while bleeding both the front and rear brakes, or only the front?<<

The Metering Valve opens at approximately 75 psi.

If there is air in the front lines and you press on the brake pedal the air will compress and probably not push the metering valve open.

If you are pressure bleeding with 20# of air, it probably will not open a 75# metering valve, if there is a lot of air in there.

If you are vacuum bleeding with 25 hg of vacuum, it probably will not open a 75# valve.

People, look at the three valves in the picture above. Any BS info you have read on the internet about the interaction between the three valves in a combination valve is just that. Bull S.

Each of those three valves have their own job to do and are not dependent on each other and do not effect what the other does.

[weq92f]

.

I think I can see and understand how the shuttle valve isolates the rear when it drops pressure. However I'm not clear on exactly how the valve shuts pressure to the front when it slides that way.

Looks to me like when shuttle is at max displacement forward(toward metering valve) a path from inlet to inside of the housing is still there with nothing restricting it from entering the metering valve.

What am I missing?

-Kevin

[RichardJ]

>>understand how the shuttle valve isolates the rear when it drops pressure. However I'm not clear on exactly how the valve shuts pressure to the front when it slides that way.<<

It doesn't and it doesn't.

That's just internet BS. The job of the Pressure Differential Switch is to turn the warning light ON. That's all.

[1970Tex]

RichardJ will like this one...is refers to it as the "combination valve"

https://www.youtube.com/watch?v=qPLaPv8DITE

[Rust_never_sleeps]

Originally Posted by 1970Tex

RichardJ will like this one...is refers to it as the "combination valve"

https://www.youtube.com/watch?v=qPLaPv8DITE

It's a manufacturer's video. They use the correct term because they also sell proportioning valves that can be installed inline

[PbFut]

Wish I had seen that video a few years ago. Like others, I went through a steep learning curve on this relatively simple device. The valve in the video still appears to be a painted version of the ebay $50 part and some additional fittings. $115 is a fair price for not having to go through the pain of figuring it all out. One thing to note, the electrical switch they include is for a later style. I think 1978 and up. You can source the correct electrical switch from In Line Tube for $14. Part number PR102A. Screws right in the same port and will eliminate swapping/splicing in the connector supplied with the wrong switch in the kit. Last point. On our trucks the very front top port, slightly angled, was not a port for optional pressure line like is machined into these new bodies and mentioned in the video. Our original blocks had a bleeder nipple and the port was machined differently to accommodate. I suppose it was used to bleed a new master rather than bench bleed. That is the tip to look for when verifying if the combination valve has been replaced at some point.