1974 F-model Gear Warning Throttle Adjustment

[AlbertF]

After my 1974 M20F came out of annual, the gear warning system was now functional.  It had not been working for the 6 months I owned the plane.  However, I found that in flight as soon as I pulled the throttle back to below 22-21 inches, the gear horn would go off (it should go off maybe 10-11).  This system is different than other gear warning switches I've seen on Mooneyspace which looks like a switch on the throttle cable which can be adjusted along the cable.  On my 1974 F, it is a switch and arm inside the throttle quadrant.  The switch (best seen in IMG_2614) has a metal arm that extends out and rests on a small adjustment plate (IMG_2615) with a tip that catches on the plate (IMG_2613).  When the throttle is forward, the plate puts pressure on the metal arm which depresses the red button.  As the throttle is pulled back, pressure is released and at a certain point the "cupped tip" of the metal arm is lifted by the friction of the adjustment plate.  

The problem is that the pressure and lifting of the metal arm happens almost immediately (about 22 inches).  I have adjusted (under supervision of the mechanic) the plate all the way forward and all the way back by loosening and tightening the nut (IMG_2615), with very little change.  The horn comes on about 22-21 inches.  I have adjusted (slight bending) the little metal arm, but that doesnt work either.  If I adjust it too much, it loses all connection to the throttle arm and adjustment plate.

I'm almost wondering if the metal arm is broken and may have been longer at some point.  Has anyone worked on this part before?  Could it be that the little "cupped tip" on the metal arm should actually be longer and extend UNDER the adjustment plate to give the ability to actually adjust it?  Right now the cupped tip catches on the adjustment plate and relieves pressure very quickly, whereas if it were longer (extending beneath the adjustment plate) would give the ability to adjust the actual pressure on the metal arm versus having it snag and be pulled up by movement of the throttle lever.  

Sorry, a little complicated and probably using wrong engineering terminology, but if you've seen this before and can tell 1) whether it can be adjusted as is or 2) the arm is actually broken, I'd appreciate it.  Thanks!

[carusoam]

Albert,

do you have the throttle quadrant with that?

do you have electric gear with that?

 

I am more familiar with the manual gear and push/pull controls...

 

The gear warning requires two inputs...

1) The gear being up... as easy as a limit switch

2) The throttle being pulled back.... a mother limit switch that falls into a machined valley in the throttle cable...

 

There are pics around here on how to adjust the position of the switch to best match the valley...

This is a fuzzy memory of things I have seen around here... not a mechanic...

Best regards,

-a-

[AlbertF]

Yes, it is a throttle quadrant with electric gear.  Everything works fine except for when the gear warning comes on.   Yes, I can hear the micro-switch click when I start pulling back the throttle, so yes, I can adjust with reasonable certainty and know where the micro-switch is opening.  It happens after pulling just a small amount.  I have adjusted the plate all the way forward, middle, and all the way back, but the "click" occurs very early.  The more I think about he problem, the more I think the metal arm on the switch is broken.  It grabs on the plate, and something tells me that is not the best engineering solution.  I'm thinking it should be longer and go underneath the plate instead of getting caught on it.  If it were to go underneath the plate, then adjusting the plate will change the point of pressure.  As is, he grabs on the plate with the broken(?) tip.  See my rough drawing.

Picture #2 shows the tip which rests ON the plate and I think it should be longer to go UNDER the plate.  I am going to pull it out and look at it closer.  Thanks ya'll.

[Yetti]

Did they change anything on the Fuel Servo end?

[carusoam]

Before spending too much time redesigning things...

Consider finding what changed.

Most things in the Mooney worked very well as designed and built...

It might even take a decade or so to find out... that you don’t have something set Up properly... 

I’m still learning about my M20C... that I haven’t owned for a decade....

Best regards,

-a-

[AlbertF]

Thanks for all the help.  I pulled it out yesterday (under supervision) and found the switch (a Micro USA JS-220 by the way) is the correct micro-switch arm length.  It looks a little worn from messing with it up and down, but I straightened it out.  What I did notice after playing with it 50 times is the cam has scratches on it which catches on the end of the switch arm.  I wonder if this is an issue because even with lube (as Freemasm suggested) it would catch.  I'll ask my A&P to file those down and lube it up and see if I get different action.