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Elevator trim making clicking sound


NotarPilot

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Seems my elevator motor no longer wants to engage. When I engage the trim switch I hear one click sound in either direction. Push up, one click. Push down, one click. No motor sound, no grinding, manual trim works fine and the plane came out of annual less than 2 months ago so it was recently lubed.

Now I'm not sure if the trim motor came standard with the 78 201s or if it came part of the S-Tec 30 AP I have. Unfortunately I was alone while troubleshooting so I couldn't stick my head in the avionics bay to determine where the click was coming from. Any ideas if it can be a solenoid, relay or the motor that went TU? I don't think it's the switch since I'm hearing the clicking sound.

Lastly, does anyone know the part number for this? I don't see it clearly in the parts catalog.

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4 hours ago, NotarPilot said:

Seems my elevator motor no longer wants to engage. When I engage the trim switch I hear one click sound in either direction. Push up, one click. Push down, one click. No motor sound, no grinding, manual trim works fine and the plane came out of annual less than 2 months ago so it was recently lubed.

Now I'm not sure if the trim motor came standard with the 78 201s or if it came part of the S-Tec 30 AP I have. Unfortunately I was alone while troubleshooting so I couldn't stick my head in the avionics bay to determine where the click was coming from. Any ideas if it can be a solenoid, relay or the motor that went TU? I don't think it's the switch since I'm hearing the clicking sound.

Lastly, does anyone know the part number for this? I don't see it clearly in the parts catalog.

Steve -- I would do as Lance suggests and have the switch checked. As you know, it is an expensive switch and it is also used pretty heavily so I would venture to say it is a likely failure point. What you need to do is buy that autotrim option and you won't need to use that expensive switch :)

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On my 77J the trim switch goes to a box that I originally and mistakenly thought was the voltage regulator but it's not. It's another box whose function I'm still wondering about. That is where the "click" noise comes from when the switch is depressed.

When I pull the circuit breaker for the trim motor I believe the box still makes noise- if I turn off the trim rocker switch it no longer makes noise.

How's that for precise. More like a description on car talk.

Sent from my iPhone using Tapatalk

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1 hour ago, LANCECASPER said:

On most of these switches it's not just one switch. As an example, the King switch uses three switches bundled together, one of them might activate a relay which is the clicking noise but if one of the three isn't working, then no trim.

I'm reluctant to check the switch being the PIA it is to unsolder and remove it.  I recently had to have everything removed for the removal of the yokes last year and it's got about 9 pins and you really need to be careful about remembering which wire goes to which pin.  Or is there a way to check it without removing it?

Based on the clicking sound, is there a possibility it could be the trim motor?  I was thinking of maybe clipping 12 volts onto the motor to see if it works but looking at it I don't think that would be that easy either.

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You must be really good at something to allow you the financial ability to own an airplane. Take it to the best shop where they are really good at what they do and they won't be learning on your dime. They do this everyday and have seen it before and will get it right. There are things that are fun to tinker around with on our airplanes and sometimes we can get it right and it feels good. The complexity of trim switches and autopilots and trim servos are best left to the experts. I had a trim  problem which turned out to be the trim switch. The guys at Central Texas Avionics in Georgetown TX knew exactly what it was in about 5 minutes. They rebuilt the switch and the total time and labor was just over $460. I never had another issue with trim on that airplane after that.

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Wiggle the connector on the disconnect relay. It is the mysterious box on the firewall. Stick your head down there, reach up and actuate the trim then wiggle the connector and see if the trim starts to run. In my experience it is much more likely to be the relay or connector then the switch.

This all assumes that you have a Century Trim system.

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Check the wires running through the control yoke. When they get chafed they can cause all kind of problems.....like my trim sticking "randomly" driving both my A&P mad for the rather long while it took to figure it out. He replaced the wires and all is good.

Could the clicking be related to something shorting due to chafing?

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Thanks for the excellent advice from everyone.  I think I'm going to take Lance's advice and find the best shop around who can diagnose this problem.  Does anyone know if these trim systems came with the early model Js or were they aftermarket?  Reason I ask is I can't seem to find the part number in the parts catalog.  I'm curious how much these trim motors are and who is the supplier...  S-Tec?  I have an inkling that the motor is the failure point, but I could be wrong.  We'll see.

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I rewired (installed a new switch) an entire trim switch once only to find out the AP disconnect switch was bad. This is actually more common than the switch going bad. I was about to pull the servo motor when I found some help at Western avionics at SNA. Give them a call. Talk with Scott or Stan. 

-Matt

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I have almost the exact same problem. We cleaned the switch with electrical cleaner last spring and it worked for a while. Now I engage the switch and push forward and hear a relay in the tail section. Interestingly, it won't do anything else until I move the manual trim, and you can feel a clutch or something release. After moving the trim manually, and only after moving it manually does it engage the relay again, but the motor does not turn. Same for up and down, and same thing with the manual trim having to be moved to "reset it". 

She is in for annual inspection and the IA is going to take a look at it. I'll post again if we find a solution. I showed him MS threads on this and info on the trim jack screw from N201MKTurbo and others earlier this year and he said it has been VERY HELPFUL. Will address the new SB on this too. 

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