Anyone have a "Pilot Valve Assembly #2965" laying around?

[Zippy_Bird]

Hi All,

This is my first post.  Recently bought my first bird... a 1966 M20E Super-21.  Definitely a step-up from the Cessna 172 rentals!  Very glad I went Mooney and very grateful to be a part of this super cool community!

Been having a blast flying and learning all the M20E systems but this of course has revealed the issues.  One issue in particular is more loathsome than the others, and that is my fight with the Mooney Positive Control (PC) System or more specifically the Brittain model LSA-2 Stability Augmentation system.  This version has a remote vacuum-only gyro behind the panel ignition switch and has the trim knob on the yolk.  The system is mostly intact and can be trimmed for level cruise BUT... I cannot turn the darn thing off.  As most know, there is a vacuum release plunger at the pilot yolk left thumb that is "supposed to" disable the system by operating the Pilot Valve #2965, but that does diddly squat for me.  I have the plunger fully removed and the system stays operational.

I am happy to have a working-ish PC system, but I am getting tired of fighting it in the pattern when I'm turning base and final.  I'd really like to get the plunger button feature working as it should.  After studying the Brittain installation diagrams and Brittain troubleshooting guides my thinking is it MUST be this part (Pilot Valve #2965).  Of course, many times in my life I have been certain of something and then found out I was certainly wrong.

Does anyone have a spare part, know if this part can be serviced, or have alternate theory?

Thanks,

Zach

[N201MKTurbo]

I may have one. If I was you , I would take it apart, clean it and put it back together. I can't imagine it is more than a diaphragm and a few ports. I will check by box of Brittan parts. 

[Hank]

I almost never press the yoke button to disable PC. The extra pressure reminds me to not overbank in the pattern. 

You are aware that it's not a "switch" to turn PC on and off, right? To disable PC, you have to hold the.button down, and releasing it reactivates the system. It's just a large vacuum leak that you must hold open.

Of course, with the valve physically removed, PC should not work. Back in the day, haters put rubber bands from broccoli around the yoke to hold the button down, or slid a plastic 35mm film canister over it . . . .

[A64Pilot]

I remember it as a little boy my Father would let me dodge clouds, pretty much 60 years ago I guess?

But if the valve is completely removed and the system is still operational it makes me think the stoppage is upstream of the valve? 
Plus if the valve works like I think it does it ought to be simple to check by simply putting the hose in your mouth, pulling a slight vacuum and seeing if it breaks vacuum.

I don’t think I would be quick to disassemble the thing until I was sure it’s the problem.

Just my opinion but I believe it’s saved people in the past that went inadvertent IMC, at least I think Mooney’s have a low fatality for inadvertent IMC and it’s the only thing I can think of that might explain why.

Edited July 14, 2023 by A64Pilot

[David Lloyd]

Several decades ago I had a '65 with the opposite problem.  Turned out the spool in that housing was stuck with gunk from the unfiltered air that comes through the valve.  Really simple to take apart, clean and reassemble.

[takair]

They do get dirty and gum up. Rather simple but delicate. Start by cleaning the screen. They do show up on eBay and here. I think there was a PC and valve recently. Might be worth having spares. They are good systems. Start by finding the valve and taking pictures. Will get you through this. 

[Zippy_Bird]

Thank-you all for the comments and advice.  @takair you were correct.  To my surprise there "was" one on eBay that I quickly snatched up.  In the future I'll start my searches there.  Once I receive this part I'll test for function, then depending how bold I'm feeling may perform exploratory surgery and cleaning.  I'll take pictures and follow-up as things progress!  Z

[Kevin Westbrook]

Zippy bird call me Kevin Westbrook about your 2965 I worked at Brittain for 40 years 539-292-0474

[Echo]

Hi Kevin

[McMooney]

Hope you get it working, I love the pc system in my E. will be missed when i upgrade the AP.