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Old 04-06-2021, 08:18 PM   #1
Bbarbeau
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Part No for Brake Combination Valve

I think my combination valve maybe stuck but the opposite of what Iíve seen most other posts about - the front brakes are very weak. I noticed this because I bled them and the front had very little flow. This is on a 72 C20c, disc/drum.

Iím in Canada and canít seem to find one of these at Napa. Wondering if someone has a part number for a combination valve that I can try and find closer to home.

Unless thereís something I should be doing with the existing valve? Thanks!
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Old 04-06-2021, 09:13 PM   #2
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Re: Part No for Brake Combination Valve

I've had trouble finding an original OEM type, they aren't something you can grab at NAPA. Having said that, since you mentioned very little flow to the front circuit, it sounds as though the shuttle valve may have been tripped (is your red brake light on on the instrument panel?). The valves are usually centered or fully engaged front or rear (to isolate a low-pressure, leaky front or rear circuit), haven't seen one that is partially engaged, but I suppose it could be possible. Anyway, you may want to take a stab at resetting the shuttle valve for the brake warning light. The easy way (which seems to seldom work for me anyway) is to slam on the brakes full force (not when moving) a time or three. If you don't have any leaks it could/should recenter the valve. There is also a proper way to reset it with tools, but who doesn't want to just stomp on the brake pedal? If it doesn't work, and it probably won't, it's worth breaking out your shop manual and reading the procedure for properly resetting the valve.
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Old 04-07-2021, 12:11 AM   #3
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Re: Part No for Brake Combination Valve

I got mine on ebay....lots to choose from.
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Old 04-07-2021, 09:09 AM   #4
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Re: Part No for Brake Combination Valve

Inline tube
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Old 04-07-2021, 11:20 AM   #5
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Re: Part No for Brake Combination Valve

Before changing the valve check the pressure between the valve and the master cylinder. It is far more likely that one of the rubber items in the brake system has failed, compared to a failure of a part with no rubber components. The rubber items will degrade over time or can physically react to different kinds of brake fluid.
The cups in the master cylinder and the hoses would be my number one items to check.
And if pressure tests of the master cylinder check out only then I would remove the valve to clean and verify the spool inside was stuck before buying another one.
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Old 04-07-2021, 11:36 AM   #6
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Re: Part No for Brake Combination Valve

I just ordered these parts for my neighbors 71 , He tried bleeding his brakes without the tool and lost his front brakes .

https://www.youtube.com/watch?v=xrjENVu1Bxk start video at 2:40


https://www.summitracing.com/parts/clp-pv-2

https://www.summitracing.com/parts/clp-pv-tool
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Old 04-07-2021, 11:39 AM   #7
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Re: Part No for Brake Combination Valve

Thanks for the replies everyone.

Do you think the reason they aren't at NAPA because they don't fail often?

I did try to center it manually but it appeared to already be centered. The dash light isn't on but that's because I discovered that the wire is totally disconnected (sigh). When I checked the valve with a meter it doesn't seem like the valve is triggered because there isn't continuity.

Interesting thought about the other components, thanks for the suggestion. Master cylinders are fairly cheap - I'll check flow and if it's suspect, replace it then. Will have a look at the hoses this afternoon. Probably a good idea to just replace those since it's new to me.
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Old 04-07-2021, 01:32 PM   #8
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Re: Part No for Brake Combination Valve

Still?

A Combination Valve is a COMBINATION of THREE separate valves. The three separate valves are COMBINED into a single unit to save all the plumbing necessary to get them connected and operational.

These three valves operate TOTALLY INDEPENDANT of each other.

This isn't rocket science, it's economics.

The first image shows the later style Combination Valve.
The second image shows a Metering valve, a Pressure Differential Switch, and a Proportion Valve.

The only difference between the first image and the second is the extra flared lines needed to connect them all together.

The pin, under the dust cover must be held OUT when manually bleeding this type of Combination Valve or the individual Metering Valve,

If the front lines are bled properly, this pin will push OUT, anytime you apply the brakes.

This style Combination Valve can be held out with a tool while bleeding.

The older style Combination Valve has a Metering Valve pin that must be held IN, while bleeding.
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Old 04-07-2021, 01:58 PM   #9
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Re: Part No for Brake Combination Valve

Another image showing ONE Combination Valve used to replace three independent units. Three independent units that operate, totally independent of each other, doing three separate jobs.

Second image shows an aftermarket Metering Valve. It has a dust cover and a pin that needs to be pulled OUT while bleeding. It doesn't push the piston or the shuttle valve in a Pressure Differential Switch Block.
The metering Valve has it's own job to do.

If there is air in the lines between the Metering Valve and the calipers, that air will compress and the Metering Valve will not open properly to allow bleeding all the air out of the lines. That is why the valve must be held open while bleeding.

The original style GM metering Valve is the large round item used on late 60's cars.

The Metering Valve opens with 50 to 75 psi, depending on application.
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Old 04-07-2021, 08:08 PM   #10
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Re: Part No for Brake Combination Valve

Thanks all,

Here's a photo of my combination valve - I believe it's the factory one. I will have a look at the front when pressing the pedal to see if there is any movement with brake pressure.
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Old 04-08-2021, 09:01 AM   #11
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Re: Part No for Brake Combination Valve

Quote:
Originally Posted by Bbarbeau
Part No for Brake Combination Valve
Back to the original question:

Delco = 5474421

Bendix = 6271406

Kelsey Hayes = 6271407
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Old 04-08-2021, 09:15 AM   #12
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Re: Part No for Brake Combination Valve

A lot of conversation here ...but one of the things I never see discussed is that the valves are not really "one size fits all".

If you look at the engineering brake release charts there are different meter/split/slope characteristics for different families of vehicles, typically based on vehicle model, body style and CG location, at curb weight and GVW.

[Actually - all of the variables in the brake system can be used to "tune" the brake balance, including friction material (size, and composition), caliper piston diameter and rear wheel cylinder diameter. They all work together as a system].

Buying a generic aftermarket combination valve off the shelf without this meter/split/slope detail is a bit like buying a generic carburetor and slapping it on, with no CFM information, expecting it to work perfectly under all operating conditions.

K
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Old 04-08-2021, 11:37 AM   #13
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Re: Part No for Brake Combination Valve

Okay, that's interesting (and helpful). I did notice that the aftermarket ones have very little detail so I will look if I have to replace it - hoping to test it this afternoon.

Quote:
Originally Posted by Keith Seymore View Post
A lot of conversation here ...but one of the things I never see discussed is that the valves are not really "one size fits all".

If you look at the engineering brake release charts there are different meter/split/slope characteristics for different families of vehicles, typically based on vehicle model, body style and CG location, at curb weight and GVW.

[Actually - all of the variables in the brake system can be used to "tune" the brake balance, including friction material (size, and composition), caliper piston diameter and rear wheel cylinder diameter. They all work together as a system].

Buying a generic aftermarket combination valve off the shelf without this meter/split/slope detail is a bit like buying a generic carburetor and slapping it on, expecting it to work perfectly under all operating conditions.

K
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Old 04-08-2021, 06:10 PM   #14
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Re: Part No for Brake Combination Valve

Quick follow up - the pin does indeed move as expected. I’m going to see about making or otherwise improvising a tool to hold it in to bleed again and hopefully that solves my problem!
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Old 04-08-2021, 06:41 PM   #15
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Re: Part No for Brake Combination Valve

That Kent-Moore tool J-23709 looks like it would be pretty easy to make!

K
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Old 04-08-2021, 11:30 PM   #16
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Re: Part No for Brake Combination Valve

Quote:
Originally Posted by Keith Seymore View Post
Back to the original question:

Delco = 5474421

Bendix = 6271406

Kelsey Hayes = 6271407
Hi, may I ask what does that page come from, and is the book available online as a reference as far as you know?

Once a person knows a part number, are there technical details about the part available, such as measurements or technical drawings?

The reason I'm asking is because on this other thread we are interested in finding the difference between manual and power brakes master cylinder for a 71-72 C-10 pickup (not Longhorn, not C-20, C-30 etc.), such as what is the bore size. http://67-72chevytrucks.com/vboard/s...d.php?t=807819
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Old 04-09-2021, 12:05 AM   #17
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Re: Part No for Brake Combination Valve

I made a bleeding tool for our '72 C20. Our "Combination Valves" look the same. I see that you have a "Trailer Brake" system plumbed in there. Ours had a Kelsey-Hayes Brake controller plumbed in. I could not find a factory combination valve, so I'm eventually having my combination valve re-conditioned. Getting ready to install a new engine and transmission.
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Old 04-09-2021, 08:58 AM   #18
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Re: Part No for Brake Combination Valve

Quote:
Originally Posted by Keith Seymore View Post
Back to the original question:

Delco = 5474421

Bendix = 6271406

Kelsey Hayes = 6271407
I am also needing one of these. Those 3 p/ns do not show in any search I have done as remotely available today. Is that the same as Delco 172-1353? There are aftermarket valves available on Ebay and Jegs, but the price varies widely. The interchange appears to be most trucks and big cars like 70s and 80s. Are any of the aftermarket ones any good? Mine (on '83 K20) has the light on, I have pushed and pulled the pin but it does not move. I have a new Delco master cylinder to put on at the same time, but I don't really want to open up the system until I have all the parts to fix it on hand.
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Old 04-09-2021, 10:04 AM   #19
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Re: Part No for Brake Combination Valve

Oh, I didn't notice initially that you have the real deal tool, nice!

Quote:
Originally Posted by PepperTreeGarage View Post
I made a bleeding tool for our '72 C20. Our "Combination Valves" look the same. I see that you have a "Trailer Brake" system plumbed in there. Ours had a Kelsey-Hayes Brake controller plumbed in. I could not find a factory combination valve, so I'm eventually having my combination valve re-conditioned. Getting ready to install a new engine and transmission.
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Old 04-09-2021, 10:21 AM   #20
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Re: Part No for Brake Combination Valve

So this is odd timing but I just had this issue on my monte carlo ss a couple days ago.

I was able to crack the rear bleeders and violently slam on the brake pedal, and had a friend close the bleeders after. Did that a few times and my front brakes came back.

I guess you have the potential of moving the valve and blocking off the rears but this didn't happen.

I have a custom brake set up on this car so I will be removing this combo valve and going another route at a later date but it stops again so that's always a plus.
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Old 04-09-2021, 03:23 PM   #21
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Re: Part No for Brake Combination Valve

>> and violently slam on the brake pedal, <<

Where do people get this internet nonsense about jumping on the peddle to fix some problem?

The piston inside the Pressure Differential Switch will not move if the pressure on both ends of the piston ARE THE SAME.

If there is 20 psi on one side and 20 psi on the other side, the piston will not move.
If there is 800 psi on one side and 800 psi on the other side, the piston will not move.

IF, the piston has already been pushed to one side because of a previous and now repaired problem and you put 800 psi on one side of the piston and 800 psi on the other side, THE PISTON WILL STILL NOT MOVE and the light will stay ON.

You must manually and intentionally remove some of the pressure on one side to alter the balance.
The problem is deciding which way the piston needs to be pushed.

Let's say you previously had a problem in the rear. The higher front pressure would have pushed the piston to the rear. To correct this after the repair, you must crack a front bleeder and SLOWLY use the now higher rear pressure to push the piston back to center and turn the light OFF.

DID I SAY SLOWLY? No jumping.

If you jump on the damn pedal, all you will accomplish is to push the piston past center and all the way to the front. The light will still be ON. You will be standing there scratching your head or your arse, don't know which one and won't know where the piston is.

>> I have pushed and pulled the pin but it does not move. <<

The pin on the front of the Combination Valve is part of the Metering Valve. If the pin will not move in or out, The Metering Valve is gummed up or damaged in some way.
Remember that the pin movement is different for the Metering Valve in the different Combination Valves. On some types the pin moves in and on others it moves out.
Be sure you know which style you have, before you try jamming that pin in there thinking you can somehow push the switch piston and turn the light off.

Summit sells replacement Metering Valves that CPP uses in their Combination Valves. As you can see, there isn't much to it.

They don't say at what pressure this valve opens and my guess is that if you ask CPP, they wouldn't have an answer. I don't think the pressure is really that critical unless you have an old soft riding barge with a real nose-dive problem.
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Old 04-09-2021, 04:40 PM   #22
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My post said to open the bleeder in the opposite side you are having problems with. I tried the slow method and it didnít work.

I did this Thursday night and it fixed the problem.....Richard

Quote:
Originally Posted by RichardJ View Post
>> and violently slam on the brake pedal, <<

Where do people get this internet nonsense about jumping on the peddle to fix some problem?

The piston inside the Pressure Differential Switch will not move if the pressure on both ends of the piston ARE THE SAME.

If there is 20 psi on one side and 20 psi on the other side, the piston will not move.
If there is 800 psi on one side and 800 psi on the other side, the piston will not move.

IF, the piston has already been pushed to one side because of a previous and now repaired problem and you put 800 psi on one side of the piston and 800 psi on the other side, THE PISTON WILL STILL NOT MOVE and the light will stay ON.

You must manually and intentionally remove some of the pressure on one side to alter the balance.
The problem is deciding which way the piston needs to be pushed.

Let's say you previously had a problem in the rear. The higher front pressure would have pushed the piston to the rear. To correct this after the repair, you must crack a front bleeder and SLOWLY use the now higher rear pressure to push the piston back to center and turn the light OFF.

DID I SAY SLOWLY? No jumping.

If you jump on the damn pedal, all you will accomplish is to push the piston past center and all the way to the front. The light will still be ON. You will be standing there scratching your head or your arse, don't know which one and won't know where the piston is.

>> I have pushed and pulled the pin but it does not move. <<

The pin on the front of the Combination Valve is part of the Metering Valve. If the pin will not move in or out, The Metering Valve is gummed up or damaged in some way.
Remember that the pin movement is different for the Metering Valve in the different Combination Valves. On some types the pin moves in and on others it moves out.
Be sure you know which style you have, before you try jamming that pin in there thinking you can somehow push the switch piston and turn the light off.

Summit sells replacement Metering Valves that CPP uses in their Combination Valves. As you can see, there isn't much to it.

They don't say at what pressure this valve opens and my guess is that if you ask CPP, they wouldn't have an answer. I don't think the pressure is really that critical unless you have an old soft riding barge with a real nose-dive problem.
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Old 04-09-2021, 06:00 PM   #23
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Re: Part No for Brake Combination Valve

All things considered sometimes it's easier , Faster . and safer to replace 50 year old parts rather than repair or chase a original 50 year old brake part to replace the original and that may or may not last ?

I mean hey , It's your brakes !
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Old 04-09-2021, 07:34 PM   #24
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Re: Part No for Brake Combination Valve

A new part may or may not last.
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Old 04-09-2021, 08:39 PM   #25
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Re: Part No for Brake Combination Valve

Quote:
Originally Posted by Keith Seymore View Post
A lot of conversation here ...but one of the things I never see discussed is that the valves are not really "one size fits all".

If you look at the engineering brake release charts there are different meter/split/slope characteristics for different families of vehicles, typically based on vehicle model, body style and CG location, at curb weight and GVW.

[Actually - all of the variables in the brake system can be used to "tune" the brake balance, including friction material (size, and composition), caliper piston diameter and rear wheel cylinder diameter. They all work together as a system].

Buying a generic aftermarket combination valve off the shelf without this meter/split/slope detail is a bit like buying a generic carburetor and slapping it on, with no CFM information, expecting it to work perfectly under all operating conditions.

K
It's in the same ballpark as putting a Corvette master cylinder on a non-Corvette. There's no consideration about any of the criteria you've posted when people do that, or other modifications, for that matter. It's a matter of luck and not having to use the braking system in the minimum and/or maximum cases it was designed for.
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