Prop. valve questions

[jcd9730]

Two questions here. First, in the picture, I'm supposed to push that button in while bleeding, right? I can't push it in, and my brake light is staying on.

Second, for the brake warning light, all it is is a wire from the prop. valve to the ignition switch, then from the ignition switch to the dash, right? Just want to check, because the light stays on

[SS Tim]

This might have been best added to your earlier thread.
http://67-72chevytrucks.com/vboard/s...d.php?t=636336

Hopefully you do not have a B+ wire running to the prop valve.
The correct routing is power to the lamp from the ignition+. Then the lamp is grounded by the prop valve if it is off center due to an internal pressure differential.
I'd strongly suggest downloading a factory service manual for your truck (if you do not have one) to see the correct schematics and pinouts. It will also have specifics on brake bleeding and prop valve operation.

RTFM ... Read The Factory Manuals... download 'em here[/B]

[Stocker]

There's a clamp made to hold the button in as you bleed the brakes. This keeps the valve centered, which keeps the brake warning light off. I don't own the correct clamp..... After you've finished bleeding, press down VERY HARD on the brake pedal (may take more than once) and the valve should re-center, which turns the light off.

[jcd9730]

I read through my service manual, and wired the warning light as shown in the diagrams. I am just curious if the light staying on could be a ground issue with the ignition switch? Just guessing here. Also, I can't push the pin in on the proportioning valve, it's stuck. Should I replace the valve? Seems stupid to spend $100 on a valve just for that light

[mgchevyparts]

If wired correctly the light comes on when the internal shuttle valve moves due to low pressure in either front or rear brake system. Often the valve is "off centered when bleeding brakes. To recenter, crack open one front and one rear bleeder at same time and pump brakes, valve should re-center and light will go off.
The wire to the prop valve is a ground wire for that light circuit, when the valve moves off center it makes contact with the prop valve body which completes the ground leg and presto the dash light comes on! The shuttle valve moves in the direction of lower pressure to block off the flow so you don't loose all your fluid(safety feature).

[mgchevyparts]

Originally Posted by jcd9730

I read through my service manual, and wired the warning light as shown in the diagrams. I am just curious if the light staying on could be a ground issue with the ignition switch? Just guessing here. Also, I can't push the pin in on the proportioning valve, it's stuck. Should I replace the valve? Seems stupid to spend $100 on a valve just for that light

If the shuttle moved it'll restrict fluid flow to that side of the system, you need to re-center it.

[mechanicalman]

This happened to me about 28 years ago. You will need to remove the switch from the block and attempt to break the valve loose through that small hole, and do have an o ring assortment on hand for that. I was able to do it on mine, but yours is likely a lot older than mine was when I did it. I believe if you can get it to move then you might be able to use the button to hold while bleeding, however you may have a seized button from external rust.

Actually, from looking at the picture, your button appears to be either stuck in or broken off; rubber boot long gone. You may need a new valve.

[jcd9730]

Tried recenter the valve like suggested, and no change. mechanicalman is probably right, I'm gonna try replacing the valve I guess.

[mgchevyparts]

If fluid flows freely to both front and rear systems then it may very well be an electrical situation. If the valve moved then either the front or rear will not get but a trickle of fluid when you bleed.

[Stocker]

Does the light stay on if you remove the wire from the prop. valve?

[jcd9730]

No the light goes out with the wire removed. The rears have always bled less fluid than the front, I just never thought anything of it til now. A new valve should be here in a few days so hopefully that fixes it.

[RichardJ]

Most of you gentlemen are seriously misinformed about your brake system.
In the first place, that is not a proportioning valve. That is a Combination Valve. There are three sections with completely different functions, ALL COMBINED into one unit as you can see in the first image.

The proportioning valve is in the rear in your picture and has its own job to do.

The pin sticking out the front is part of the Metering Valve. The metering valve has nothing to do with the light switch and is not connected to it.

Some metering valve pins move OUT under pressure and other metering valve pins move IN under pressure.

I am guessing, but I believe your pin should move IN under pressure, but it seems to be stuck in the IN position.. It will move IN when the pressure INTO the metering valve reaches about 50 lb. (another guess, because they vary with application)

See if your pin moves out when you push on the brake pedal, then you need to find a way to hold it OUT while you bleed the front brakes.
Have a helper push on the brakes and see if the pin comes out. If it does not, try bleeding the upper hose by using that bleeder valve on the top of the metering valve. Connect a rubber hose from that bleeder into a bottle, With your helper, try bleeding there and see if the pin comes out enough to grab.

If you can get the pin to move, bleed the brakes, then worry about the brake switch.

Below or holders used for the two different types of pin operation.

[jcd9730]

So I replaced the proportioning valve with one from cpp, geld the metering valve out with some vise grips and bled all around. Still can't get the light to go out. I tried stomping on the pedal, tried bleeding one front and one back brake at the same time, still can't get it to go out. I don't see how it could be the brakes themselves. Could a wiring problem cause it to stay lit when the engine is running? I wired it according to the diagram.

At some point someone had cut the wire to the valve, and so I just ran a wire to the terminal on the ignition switch and the light now comes on.

[Fitz]

Originally Posted by jcd9730

So I replaced the proportioning valve with one from cpp, geld the metering valve out with some vise grips and bled all around. Still can't get the light to go out. I tried stomping on the pedal, tried bleeding one front and one back brake at the same time, still can't get it to go out. I don't see how it could be the brakes themselves. Could a wiring problem cause it to stay lit when the engine is running? I wired it according to the diagram.

At some point someone had cut the wire to the valve, and so I just ran a wire to the terminal on the ignition switch and the light now comes on.

The prop valve is just a hydraulic switch. It shuts off either the front or rear brake circuit if there is a loss in pressure on either circuit. Air in one circuit acts the same as a pressure loss so you need to get the valve centered BEFORE doing anything else. The picture shows the piston in the prop valve in the on and off position. You can tell if the switch is "on" by testing the contact with a multimeter between the electric contact and ground. If the contact is shorted to ground the piston must be recentered in the valve. Remove the nut at the reatr of the valve and the switch on the top of the valve. Be careful not to get dirt inside. Push the piston to the front of the valve and look down into the opening where the switch contact is installed. You should be able to work a pick into the v notch on the piston to move that notch directly under the opening for the switch. Insert the prop valve centering tool to hold the piston in place and replace the rear nut and install the valve. The tool will keep the piston from moving so that both hydraulic circuits will see fluid pressure. Get someone to depress the brake pedal while you open the bleeders to remove any air. When you have good pedal, remove the centering tool, re-install the switch and connect up the warning light. If you don't have the prop valve centering tool it is available from Performance On Line for seven bucks. A must have unless you like hours of frustration trying to bleed brakes with a prop valve.

[jcd9730]

Mine doesn't look like that, neither did the old one. There's nowhere to screw something like that in, there's just the metering pin you have to hold out.

I think that it's wired wrong. I tried to run a wire from the prop valve, to the ignition switch, and then another wire from the switch to the dash, according to the diagram. There is a connection, but the light will not come on at all. What am I doing wrong?

I put the multimeter on the prop. valve switch and a ground. I assume I'm supposed to test resistance, and if so there was resistance between. But there's still something wrong with the brake light wiring for sure, I just don't understand what

[RichardJ]

>> I tried to run a wire from the prop valve, to the ignition switch, <<

Obviously you haven't or you would have burned the truck to the ground by now. At the very least you would've melted every wire between the proportion valve and the ignition switch if not from the proportion valve to the ignition switch and then onto the battery.
The wire from the proportion valve must go directly into the instrument cluster brake warning light. The other side of that light is then connected to a 12 volt power source.

>>Mine doesn't look like that, neither did the old one. There's nowhere to screw something like that in, there's just the metering pin you have to hold out.<<

Fitz is not showing you proportioning valve. He is not showing a combination valve. That is a switch and nothing else. That is a stand alone switch and serves no other function other than to turn the break warning light on.

The plunger inside the switch needs to be moved to the center position, but not until after the brakes for fully bled. During the bleeding process it is very easy to push that plunger either forward or backward. The end of the truck you are bleeding will have no pressure because you have the bleeder valve open. The other end of the brake system will have pressure and push the plunger toward you. After you close that end up, all you have to do is go to the other end, crack one of the valves and push on the brake pedal until the warning light goes out.
Remember, you need a helper pushing on the pedal because you can't take your foot off the pedal with any valves open or you will suck air back into the system.

[jcd9730]

According to the diagrams, the proportioning valve is clearly wired to a terminal on the ignition switch, then from that same terminal up to the dash. Not all terminals on the switch have 12v..

I'm obviously missing something here since the light won't come on, but that is how it is wired according to the diagrams at least.

[jcd9730]

I'm wondering if maybe I should try putting a ground on the ignition switch

[mechanicalman]

Take an ohm-meter and check for continuity between the brake switch and ground. If it has continuity, then the valve is not centered. If it does not have continuity, you have it wired wrong or short to ground.

[RichardJ]

>>I'm wondering if maybe I should try putting a ground on the ignition switch <<

ABSOLUTELY! BUT. Have a Six year old standing by to dial 911 for you.


Enlarge the diagrams and take a closer look. Remember the inside and outside plugs on the diagrams are mirror images of each other. A wire pin on the RIGHT SIDE of the firewall connector, connects to a wire pin on the LEFT SIDE of the inside connector.

On colored diagrams, the wire colors are usually consistent from one plug and the outgoing wire on the other plug, BUT NOT ALWAYS.
You should be following a "20T" tan colored wire from the "BRK WARNING SW", to the upper Right corner pin on the firewall connector. "20T" tan colored wire comes out the upper LEFT corner pin on the inside connector. Follow that "20T" wire to the "Cluster Conn".

The list of connections at the right, labeled "Instrument Cluster Circuit" is for "idiot light", instrument panels. If you have a Temp gauge and an Ammeter gauge, use the "Cluster Conn" pin-out that is in the upper right corner of that diagram page.

I have been referring to the colored diagrams that are in the electrical forum section of this forum.

Wire colors are not always consistent from one plug to the wire coming out the mating connector. The wire from the distributor is labeled "20W/OR/PPL" and it mates to "12P" on the inside connector.
Sometimes wire sizes change and sometimes they split into two wires.

[jcd9730]

Welp, turns out I just needed to replace the ignition switch, and clean up all the horrible wiring the the PO did when he installed a stupid push button right next to the switch. All is well with the warning light now, didn't even need to mess with the valve. Thanks for all the suggestions everyone

[michael bustamante]

This turned into quite a thread. Now that he has figured out what was wrong with his brake light I am goin to hijack. So previous comments had mentioned to pull the button out for bleeding. But mine has the rubber boot on it and cannot be pulled out only pushed in so what is going on here? my valve came out of the 72 and everything I have read before this has to be pushed the button in while bleeding

[jcd9730]

Can't you just take the boot off? Then you should be able to see the pin you need to push in/hold out