Proportioning Valve Keeps Tripping?
 

1967 C10 - Disc conversion (power 8" booster) - master cylinder is 1" bore, and the proportioning valve was advertised when bought in the kit as a disc/drum setup.

I am having an issue with my proportioning valve.
When I go to bleed the brakes, while using the proportioning valve tool to center the shuttle valve, everything bleeds fine, no leaks and good strong flow. No air coming out anymore, I did plenty of extra pedal strokes to ensure this and had no air that I could see come out.
But when I put the brake switch back in, bleeders all closed, and press the pedal down half way, the red brake light illuminates. I have pulled the switch and confirmed the shuttle valve closes the rear brakes. Recenter, does it again.
I confirmed the rear brake shoes are at their proper adjustment with a brake drum/shoe caliper tool to get the measurement even.
Even after adjusting and all this bleeding, it seems like its either seeing a fault at the rear.

So my question essentially is how do I move forward from here?
From the factory, the front brakes are fed by 1 line off the front of this proportioning valve down to a T fitting split to both sides, and obviously rear is one that goes to a T on the differential.
Someone did say my front feed being at the top fitting (pictured) is an issue, I don't see this as an issue being this should be able to balance it, am I incorrect?

Attachment 2343742 Attachment 2343743

Re: Proportioning Valve Keeps Tripping?
 

The position of front line is not the problem.

Your PV is sensing a change which triggers the switch. Whatever direction it moves, that part (front or back) has a leak you need to find

...or the PV is bad which is rare but given source of replacement parts used in these kits, way more possible now.

Power brake disc typically use a 1 1/8" bore MC but that would not affect what PV is doing. larger bore just means less pedal stroke as the booster assist does not need the stroke a manual setup needs.

Re: Proportioning Valve Keeps Tripping?
 

In my opinion the front brake line coming off the combination valve upwards shouldn't matter because it was designed that way for two front brake lines. However, typically when using a single line with a tee, others (factory included?) used the bottom port and plugged the top. I don't think it will matter.

Someone else, on this forum, stated that their switch was too sensitive. Are you seeing a lot of movement of the shuttle valve? Having removed the switch, how much movement can it have before the light turns on?

How do you know that the proportioning valve isn't stuck in the open position? It's function is too reduce the pressure to the rear, right? What would the shuttle valve do, if the proportioning valve wasn't doing its function? I think it would slide rearward a bit. You could replace just the proportioning valve, and see if it makes a difference. Then you could disassemble the first proportioning valve to see if there was a problem.

Re: Proportioning Valve Keeps Tripping?
 

>>proper adjustment with a brake drum/shoe caliper tool <<

If you are talking about a "resetting tool" , the shoes are probably still too far away from the drums.
You should adjust until the shoes drag and then step on the brake pedal to center the shoes. You have to readjust tighter, press on the brake and check for drag again. The finish adjustment should allow you to hear some drag, but not necessarily feel any resistance when you turn the drum.

Re: Proportioning Valve Keeps Tripping?
 

Which mater cylinder do you have on there? Lift the cap off and take a pic.

Re: Proportioning Valve Keeps Tripping?
 

I have checked all fittings - no leaks. Verified visually and with a clean rag to see if theres even the smallest seepage. I am leaning towards a bad PV.

Ill need to visually see how much it moves, it moves enough to trigger but I can still manually recenter with a pick, moving the shuttle back to neutral. Its somewhat "U" shaped, and I can grab the edge of the U and pull it back, if that makes any sense.

The tool I am refering to is a tool made by Blue Point, its a giant caliper that you set inside the drum to set the diameter, and then hold over the shoes and adjust until they lightly touch. I dont believe the rear shoes are an issue; theyre adjusted to the proper drag currently and the light is still persisting after resetting the PV and verifying it is in neutral and the light is off until the pedal is pressed.

Re: Proportioning Valve Keeps Tripping?
 

My almost-new switch all of a sudden got very sensitive, even when not applying the brakes. I pulled it out and checked it on the bench with an ohmmeter. Turns out that just a very small bit of upward movement causes the switch to close. I mean we're talking .050" if that much.

Ended up using the later model switch that came with my aftermarket combo valve. Unfortunately, the wire connector is different, but that's no big deal -- just another PITA to deal with.

This is probably not your problem, since your switch closes only when you step on the brakes. But I just wanted to get this info out there -- the light flickering or being on all the time could indicate a bad ChiCom switch.

On another note, that's a dual 8" booster, right?

Re: Proportioning Valve Keeps Tripping?
 

Maybe try adjusting the backs to be stupidly tight and see if that makes a difference.
IF you still have the differential pressure valve moving, then there's air or fluid loss somewhere causing a....pressure difference

Re: Proportioning Valve Keeps Tripping?
 

Yep - 8" booster. I did flush mount to the firewall, which I was thinking may be a problem, but judging by what others have told me I am thinking I have some air really stuck. Im going to try a heavy hit to the pedal with the bleeders open and see what it gets me. Hopefully not a mess to clean up!
I actually did adjust them to the point where the wheel wont turn. Still the same. I am thinking I have a huge bubble somewhere and its possibly in the rear circuit at the prop or in the prop valve.

Re: Proportioning Valve Keeps Tripping?
 

Old school reputable mech. says old CPV vales rarely fail.

Re: Proportioning Valve Keeps Tripping?
 

Gotcha. I had better luck syringe bleeding the MC/combo valve than bench bleeding, or at least felt more certain about it.
Bought a pack of these off the River :shrug:

Re: Proportioning Valve Keeps Tripping?
 

How does the pedal feel? Can't imagine there's air in the lines after all the bleeding you've done.

Have you bled brakes in the past? Are you shutting the bleeder valve before your helper lets off the pedal? And/or submerging the bleeder hose in fluid so it can't suck in air?

Re: Proportioning Valve Keeps Tripping?
 

Ive done quite a bit of bleeding in the past. I use the one way valve "Speed Bleeders" on nearly everything, so I dont have to on/off the bleeder. I do keep it submerged though. If all else fails, I will borrow a pressure bleeder and force the system to give me an answer! :lol:

As far as pedal feel, it is soft sometimes, and sometimes when bleeding it is hard. Counterintuitive.

Re: Proportioning Valve Keeps Tripping?
 

Ive thought of this as well when I was bench bleeding the MC. That may be on the list after some abrupt pressure bleeding.

Re: Proportioning Valve Keeps Tripping?
 

When the light goes on do the rear brakes still actuate? The proportion valve when tripped will stop the fluid from going to that circuit. I would let the light come on and try to bleed the rear brakes no fluid the circuit is tripped if you get fluid then it may be the switch .

Re: Proportioning Valve Keeps Tripping?
 

See post number 5

Re: Proportioning Valve Keeps Tripping?
 

Heres that picture. I had to get it at home last night so I could post it here today. I consulted the people who sell these and they say rear is rear and front is front.

Re: Proportioning Valve Keeps Tripping?
 

From what I can hear, they still actuate. I am doing this alone so I use my phone camera to see whats going on. With the switch in, it will only send the shuttle valve backwards a small amount, and still let fluid out. When I take the switch out, it will close them entirely. At this point, I have ordered a pressure bleeder to see if I can force some sort of hidden air pockets out.

Re: Proportioning Valve Keeps Tripping?
 

The plan as of now;
1. I purchased a pressure bleeder, should be here Saturday. I will force all the air and fluid out with it if theres any.
If no avail;
2. I will replace the master and proportioning valve with a 1-1/8" master kit.
If no avail;
3. I will start going to church :lol:

Does anyone think the dual-diaphragm 8" booster with a 1" bore master is an issue? I am not thinking it is as I dont know why one would be sold if that was the issue, but now I am possibly beginning to second guess all components.

Re: Proportioning Valve Keeps Tripping?
 

Did you change the rear cylinders? May not be correct size for the system

Re: Proportioning Valve Keeps Tripping?
 

I had changed them out years ago, when I did the brakes in the rear and they operated at that time fine. That was years ago and when it was on the drum drum setup. But I couldnt imagine an issue there - as a lot of people do the disc drum conversion and I havent seen it notated that they touched the rear brakes at all.

Re: Proportioning Valve Keeps Tripping?
 

I would talk to the tech guy . The master may not be correct for your rear brake cylinder. Most places sell generic masters mostly for cars . If your rears are to large there may be a pressure differential between the disc and drum brake for a fraction of a second causing it to believe there is a leak in the rear circuit.

Maybe change out the portioning valve it could be defective.

Re: Proportioning Valve Keeps Tripping?
 

Pretty sure c10 and c20 are different the front on my c20 goes to the rear reservoir on the master

Re: Proportioning Valve Keeps Tripping?
 

I did my 72 manual disc/drum to power using the CPP booster/mc/pv. Rears went to rear of PV, front to front of PV. (pic)

O{, I think your issue is the PV or the shuttle switch in it.

OP, power front disc brakes use a 1 1/8" MC. Manual drum uses 1" MC. Either should "work" but with the 1 1/8 MC the pedal stroke will be shorter which with the booster is all that is needed.

Re: Proportioning Valve Keeps Tripping?
 

As for bleeding an M/C, I do it on the truck using these hard lines. Surprisingly, not a lot of fluid leaks out when you remove them after bleeding. Sure beats doing it using those M. Mouse kits that come with some M/Cs.

Re: Proportioning Valve Keeps Tripping?
 

That's what I was getting after, 1/2 vs 3/4 have swapped lines back and forth regarding the placement of the residual valves.

Re: Proportioning Valve Keeps Tripping?
 

I like Mike B's master cylinder bleeder lines. I was thinking about a tee off the proportioning valve port with a bleeder screw, or straight to a bleeder screw with an adapter (if manufactured), or a tube nut with hard line and vinyl hose. Isn't there a brake line coupler on the frame rail? Maybe you could bleed from there also. I think you're right, it's more likely that you have an air bubble near the start of the rear brake line. Good luck.

Re: Proportioning Valve Keeps Tripping?
 

I rigged up one of these from the old lines(after I lost the plastic pieces that came with the MC). I prolly would have never bothered with syringe bleeding had I known at the time that thrashing on the brakes creates thousands of tiny bubbles through cavitation, as does applying stupid heavy vacuum

Re: Proportioning Valve Keeps Tripping?
 

This weekend I tried the power bleeder. No dice.

I am beginning to believe I am pulling air, but not leaking fluid. I have heard numerous times now about wheel cylinders bringing mystery air in. These wheel cylinders are probably 8 years old, never used. That being said, I never had fluid in the system to test them. I am going to replace them and recheck.

Everytime I go to bleed the rears, I get micro bubbles and sometimes very small ones, but regardless I get a stream every time I open the bleeder. I ran nearly a gallon of fluid through them and still had the same situation.

I also rebled the master cylinder to ensure no air is trapped in it, and it bled clean.

Re: Proportioning Valve Keeps Tripping?
 

Kyle I applaud your persistence ! Keep at it ! Lots of people will learn from your experience..Jack

Re: Proportioning Valve Keeps Tripping?
 

If air is somehow creeping into the system (which I doubt), that means you would have a fluid leak. Have you seen signs of that anywhere?

FYI, if you are pulling fluid trough the bleeder valves using a vacuum pump like a MityVac, you will almost always see bubbles from air creeping in between the hose and bleeder valve.

Re: Proportioning Valve Keeps Tripping?
 

What are the full specs for the kit, or webpage where it is sold?

Re: Proportioning Valve Keeps Tripping?
 

It is not uncommon to pull air from bleeder nipples being loosened to bleed at the threads. A thin coat of silicone on the bleeder nipple threads prevents this. Do not use Teflon tape.

Re: Proportioning Valve Keeps Tripping?
 

He stated that he is using the speed bleeders. They come with a thread coating, although this coating could have deteriorated. A common problem with vacuum bleeding is sucking air past the bleeder threads unless the threads are wrapped.
He also said he has tried a pressure bleater.

I could see a problem with manual bleeding, if debris is holding the Speed Bleeder Valve open and the valve is not closed, each time the pedal is withdrawn. This wouldn't affect vacuum or pressure bleeding.

My only conclusion from all of the above postings is that the Primary Section of the MC has failed.

Re: Proportioning Valve Keeps Tripping?
 

You could always let it gravity bleed :shrug:

Re: Proportioning Valve Keeps Tripping?
 

Thank you. I plan to get this fixed and report back my findings! Fingers crossed.
I verified at each fitting that there is no leak, but I have seen a lot of documentation for the bores of the wheel cylinders to pull air and foul that section of line with air. I believe it was Stocker on this board who had a similar issue, and he took it to a shop and they replaced the wheel cylinders in the rear and it was solved. Plus I am thinking starting with wheel cylinders will be the most inexpensive option at this point - next would be MC.
This is a CPP front brake disc conversion kit, Inline Tube prebent lines, stock rear drums and a kit from Tom's Classic's for the booster/MC/PV
Ive tried the silicon before with not a ton of luck, but I use a small run of teflon tape on the threads (not the tapered seal and not on line fittings) as some of the folks at Hagerty suggested. Why I did this, is because when I loosen the bleeder I can wiggle it some and Im certain air is coming through when bleeding. With a small layer of teflon, no deflection is noted.
I have limited knowledge of MC operation in all honesty - would the primary section effect the rear brakes? Rear bowl is rear brakes, front bowl is front brakes. My front brakes are perfect and have zero bubbles.
I have tried this as well. Still no dice unfortunately.

Re: Proportioning Valve Keeps Tripping?
 

Might be a PITA to bypass the combination valve with temporary hard lines, but that would probably tell you where the problem is. Of course you would need the proper bending and flaring tools, along with fittings.

Is still don't see the problem being a wheel cylinder or something else "sucking in" air.

Re: Proportioning Valve Keeps Tripping?
 

Have you tried adjusting the push rod between the the boostewr and master cylinder

Re: Proportioning Valve Keeps Tripping?
 

UPDATE 3/28/24

I replaced the wheel cylinders for the rear axle, and the fluid is coming out completely air free now. I ran a ton of fluid to be sure with a pressure bleeder for extra insurance.
The pedal feels more solid at this time.
NOW, I am having a brake light come on the dash past 3/4 pedal travel. BUT, when this happens, when I bring the pedal back up past that area, it clears itself. So I am thinking I have or may be dealing with separate issues. Possibly the MC bypassing itself? I at this point get sick at the idea of bleeding brakes. LOL.

Any further pointers or ideas?

Re: Proportioning Valve Keeps Tripping?
 

But the originals were not leaking? I don't know how they could have held or drawn in air. (Play Outer Limits theme song here.)

That shuttle valve is acting very strange. Could it be moving to the front? Are the front calipers installed with the bleeder screws on the top?