Proportioning Valve Keeps Tripping?

[kwmech]

Originally Posted by KyleSeal

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.

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.

[Dashman]

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.

[Rust_never_sleeps]

Originally Posted by MikeB

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.

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

[KyleSeal]

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.

[54blackhornet]

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

[MikeB]

Originally Posted by KyleSeal

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.

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.

[dmjlambert]

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

[72SB]

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.

[RichardJ]

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.

[Rust_never_sleeps]

You could always let it gravity bleed :shrug:

[KyleSeal]

Originally Posted by 54blackhornet

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

Thank you. I plan to get this fixed and report back my findings! Fingers crossed.

Originally Posted by MikeB

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.

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.

Originally Posted by dmjlambert

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

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

Originally Posted by 72SB

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.

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.

Originally Posted by RichardJ

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.

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.

Originally Posted by Rust_never_sleeps

You could always let it gravity bleed :shrug:

I have tried this as well. Still no dice unfortunately.

[MikeB]

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.

[airdale94]

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

[KyleSeal]

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?

[MikeB]

Originally Posted by KyleSeal

UPDATE 3/28/24

I replaced the wheel cylinders for the rear axle, and the fluid is coming out completely air free now.

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?

[KyleSeal]

Originally Posted by MikeB

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?

Bleeders are on top, and the shuttle valve is moving to close the rear circuit. I am not sure if the prop valve switch is recentering the shuttle or if it is actually returning to center on its own.

I am curious - when the cap is off the master cylinder, and I press the brake pedal, there is a bit of brake fluid that 'shoots' up, to the point I just put a rag over it so it doesnt get all over the place. Maybe a few inches, is this an indication of anything?

[MikeB]

Originally Posted by KyleSeal

I am curious - when the cap is off the master cylinder, and I press the brake pedal, there is a bit of brake fluid that 'shoots' up, to the point I just put a rag over it so it doesnt get all over the place. Maybe a few inches, is this an indication of anything?

That's normal. Kinda like a miniature Old Faithful!

[MikeB]

Originally Posted by KyleSeal

UPDATE 3/28/24
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.

If you have an ohmmeter, remove the brake warning switch, then set it on a workbench and check to see how sensitive it is. As I mentioned in a post above, the brand new one I bought would close (zero resistance) when the pin barely moved -- around .050". It could be that yours has a similar problem, so even when the pressure differential valve moves just a tiny bit, the pin moves up and closes the switch.

[KyleSeal]

Originally Posted by MikeB

If you have an ohmmeter, remove the brake warning switch, then set it on a workbench and check to see how sensitive it is. As I mentioned in a post above, the brand new one I bought would close (zero resistance) when the pin barely moved -- around .050". It could be that yours has a similar problem, so even when the pressure differential valve moves just a tiny bit, the pin moves up and closes the switch.

I will check that out - Im not sure why it didnt register to me when you first said it but I will try that. Maybe as simple as a switch. Since I am away from the truck and havent tried the pedal with it running - should be pedal be harder/more firm with the booster set up when the motor is running? Or softer? Like I said I havent run it, and last I drove this truck it was manual brakes.

[RichardJ]

>>should be pedal be harder/more firm with the booster set up when the motor is running?<<

Pump the pedal a couple of times and HOLD. You should have a very high, firm pedal.

Start the engine. As vacuum builds, your foot and pedal will drop.

The booster is designed to hold vacuum for 3 applications of the pedal. If the engine dies while driving, the booster should hold plenty of vacuum to give vacuum assist in order for you to get to the side of the road.

Turn the engine off. Apply the brakes 3 times. The pedal should be higher and firmer after each successive application.

[KyleSeal]

Well, heres an update again.

Pedal gets firm about 1/4 down, and feels OK when engine is OFF.

But, when its running, its like its a 100% dry system. Put in gear (on jack stands) and brakes have zero effect in the rear, fronts I havent checked since I didnt have it actually move. I am at a huge loss right now because I have literally bled gallons through this system. Now I am thinking the MC is bad.

Thoughts?

[RichardJ]

post #34

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

[MikeB]

Do you have the tools, brake line, and fittings to bypass the combo valve? It may possible that the proportioning valve is limiting pressure to the rear WAY before it's supposed to.

Then again it might be a bad M/C like Richard says. Bypassing the combo valve will tell you where the problem is, or isn't.

[Rust_never_sleeps]

On old earth moving equipment, they'd sometimes use an oil can clamped to a hose to bleed hydraulic systems from the lowest point back to the reservoir.
You might try this with a big syringe from the farthest wheel cylinder. Looking for flow, and maybe trapped air. This way is messy, so rig up a drip pan and wash off any spilled fluid in the engine compartment

Otherwise, I agree with the above and you'll have to get clever with swapping parts or plumbing to isolate the problem

[KyleSeal]

Originally Posted by RichardJ

post #34

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

I am in this camp as well.

Originally Posted by MikeB

Do you have the tools, brake line, and fittings to bypass the combo valve? It may possible that the proportioning valve is limiting pressure to the rear WAY before it's supposed to.

Then again it might be a bad M/C like Richard says. Bypassing the combo valve will tell you where the problem is, or isn't.

So I dont have the tools handy - nor do I trust my flaring abilities at this time, so I swapped prop valves. No more brake light at all, but pedal only stops the rear tires at the bottom of the pedal (on jacks, no load)

Originally Posted by Rust_never_sleeps

On old earth moving equipment, they'd sometimes use an oil can clamped to a hose to bleed hydraulic systems from the lowest point back to the reservoir.
You might try this with a big syringe from the farthest wheel cylinder. Looking for flow, and maybe trapped air. This way is messy, so rig up a drip pan and wash off any spilled fluid in the engine compartment

Otherwise, I agree with the above and you'll have to get clever with swapping parts or plumbing to isolate the problem

I have tried this as well, at this point I am convinced I have no more air (I ran two gallons through the system, last 1.5 gallon had no air)