Residual Pressure - after Brake Proportioning Valve

Hi, I have a problem that is not porsche related but perhaps someone in the community knows how to avoid / where the problem lies.

I've just installed a Tilton Proportioning Valve 90-2003 and I have an issue with residual Pressure in the system.
Specs of the car: Single Cicuit system front: Discs, rear: Drums
No residual Pressure Valve in Main Cylinder or in the line.
The rest of the Braking system is untouched and has been run before, so the only change has been the installation of the Proportioning Valve in the line to the rears. I have confirmed the orientation in-out is correct.
Brakes have been bled thoroughly with a pressure/vacuum bleeder (+pressure at the MC and vacuum at the wheel cylinder) Brake Pedal feel is ok.

What I've recognized and confirmed is that I get a residual pressure in the rear circuit if the proportioning valve is turned in more than 2.5 Turns (of the 7.25 Turns possible).
So the rear drum is free - I close the Valve 3 turns- I press the Pedal and afterwards the rear drum is stuck. I could feel it in the test drive, and now have confirmed with the wheel off. When I attach a tube to the bleeder at the Wheels cylinder and open it I get a volume of ca 0,5cm³.

As I need a rather closed Proportioning valve to get settings right this won't work for me.

Do you have an Idea what's wrong? When I'm only closing 2.5 turns the drums are free after releasing the pedal.

That is bad behaviour for the valve. As I understand the operation, the fluid flows freely through the valve until the set-point. There appears to be a piston with a spring (and the knob sets the preload), and the line pressure moves the piston until it covers the passage. Now how the pressure after that point is reduced in a 3:1 ratio, I am not clear on. Perhaps it is a dual piston with a 3:1 ratio on the back side. What does appear evident is that the piston is not moving back properly as the pressure is reduced, and uncovering the passage to allow the fluid to flow back and release the pressure. That makes it appear to act as a line lock. Definitely something wrong happening in the valve. Tilton should be able to provide the answer.

Quote:

---

Originally Posted by davep

That is bad behaviour for the valve. As I understand the operation, the fluid flows freely through the valve until the set-point. There appears to be a piston with a spring (and the knob sets the preload), and the line pressure moves the piston until it covers the passage. Now how the pressure after that point is reduced in a 3:1 ratio, I am not clear on. Perhaps it is a dual piston with a 3:1 ratio on the back side. What does appear evident is that the piston is not moving back properly as the pressure is reduced, and uncovering the passage to allow the fluid to flow back and release the pressure. That makes it appear to act as a line lock. Definitely something wrong happening in the valve. Tilton should be able to provide the answer.

---

Yes I've already asked tilton but got no reply until now. I am wondering whether it's an error in the Valve and I should just try to get a replacement or if it is a general Problem with the setup.
We'll see

I have been talked by the vendor in buying another one (lever type this time to avoid being from the same charge) same issue. Have been talking to tilton yesterday - no idea from theier side.
If you want to have a look I made a video. (I bled the system to get the pressure out before the video)
https://youtu.be/JB-HrYsSRas

If a second unit did not fix it, then the valve is almost certainly not the problem. Doubly so if Tilton expertise cannot diagnose the problem.
Do you have the correct free play on the pedal? Does your pedal fully return or can you pull it back; it could be the pedal is sticking and the pedal cluster needs rebuilding.
If the pedal cluster has no fault, then the master cylinder is suspect. With all the bleeding you have been doing it is possible the MC was damaged internally. How old is the MC?

I have a Pressure/Vacuum bleeder that has pressure on the reservoir and vacuum at the wheel- so bleeding can't be the problem.
The front wheels turn free and it's a single circuit so the master cylinder isn't the cause. I am sure I could replicate the behavior in a bench situation.
Let's put it like that I had a polite gent on the phone but he wasn't that technical ...
I've sent an email to tilton with the link to the Video, lets see if they react.

There is not a lot of components in the system: pedal cluster, MC, Proportioning Valve, calipers and lines. The pedal cluster can prevent the MC from fully retracting, The MC can stick, the Proportioning Valve can stick, the calipers can stick as well but that cannot hold pressure. The only other device that can hold residual pressure are rubber brake lines that swell internally and act as a one way valve.

I was going to post the same thing as davep. Witnessed many headaches from rubber brake lines gone bad. Also, check the springs in the drum and make sure everything is lubed up and free moving.

Tilton came back to me - they were able to replicate the behavior in their test environment.
After that I bought an AP Racing in the and just finished installation - works like a charm - no residual pressure no matter which setting it is adjusted to.
And although it costs twice the cost of the tilton it looks and feels more than twice as solid.
The only drawback was that I had to enlarge the hole in the tunnel a lot and add new flares to the brakelines as it needs quite long threads at the connectors - luckily I had some with long threads on the shelve.
So tilton is not the way to go when choosing brake proportioning valves.

So what was Tilton's revelation on how their proportioning device creates a lock-up. Essentially that is a total failure of their device to do what is promised.