M20J - Gear not Retracting

[EricJ]

2 hours ago, WheelPantsOff said:

I did have some avionics work done on the airplane earlier this year and I want to rule that out, but I had so many issues with it, I'm having a hard time preventing that.  They also allegedly gave me a IFR/VFR check out of it without any issues.

This is mounted on a nearby bracket.  I traced out all the lines and fittings that I could see and all the B-nuts were at least finger tight and nothing obviously loose.  Is this diaphragm replaceable with a new celophane/rubber?  It's surprisingly easy to access and it seems like the switches are still hard to come by.

I've never had one apart, but they're not complicated.   Parts and replacements are not easy to find, but it might not be too tough to repair if it needs more than adjustment.

[PT20J]

The VEP switches are still manufactured. VEP is now a brand of World Magnetics (www.worldmagnetics.com). With a little calculating you could figure out the OEM part number.

654-switch-veproducts-aerospace-low-pressure-switches-specs-sheet.pdf

[1980Mooney]

13 hours ago, EricJ said:

I'd think the ASI would be off as much as the switch if it was a pitot pressure problem, unless there's something in the line between the two.

 

I think @EricJ is right. If there was a leak in the pitot line then the pressure would be low on BOTH the landing gear switch and the ASI. In that case the continuity test on the switch would trip at a normal approx 60 KIAS shown on the connected ASI. - but because of the leak, the plane would need to travel faster than 60 KIAS to create the same pressure in the pitot system. But that is not the case. 

[PT20J]

3 hours ago, 1980Mooney said:

I think @EricJ is right. If there was a leak in the pitot line then the pressure would be low on BOTH the landing gear switch and the ASI. In that case the continuity test on the switch would trip at a normal approx 60 KIAS shown on the connected ASI. - but because of the leak, the plane would need to travel faster than 60 KIAS to create the same pressure in the pitot system. But that is not the case. 

I'm not disagreeing with you guys, but we know that these things get damaged somehow and I don't know what the mechanism is. Perhaps someone that had one damaged would know what the failure mode is.

[EricJ]

42 minutes ago, PT20J said:

I'm not disagreeing with you guys, but we know that these things get damaged somehow and I don't know what the mechanism is. Perhaps someone that had one damaged would know what the failure mode is.

Forty years of thermal and pressure cycling might be enough.  The diaphragm, spring, and microswitch probably change characteristics over that much time and cycles.    Even if it's not leaking, the diaphragm might be stiffer or something.   I'm just speculating, but with old stuff you never know.

[1980Mooney]

2 hours ago, PT20J said:

I'm not disagreeing with you guys, but we know that these things get damaged somehow and I don't know what the mechanism is. Perhaps someone that had one damaged would know what the failure mode is.

You are both correct in your assessments.  I should’ve been more clear. I agree with. @EricJ that there is no leak in the tubing between the  and the ASI. And I agree with you that the only other thing that could have failed is the sensing mechanism (springs, microswitch). If the diaphragm in the switch had failed, there would be a continuous leak, which would give you a low speed reading in the ASI. 
 

I have the old style sensor, which screws directly into the back of the ASI. The diaphragm in that looks like some kind of rubberized fabric. Over time and heat mine got brittle which affected its ability to flex and therefore the speed at which it tripped.
My diaphragm also eventually developed a leak  

The newer switch looks like it’s made out of something much more durable. 

Edited August 4 by 1980Mooney