79 M20J - electric trim not working

[Papa K]

Had my first flight in my M20J today.  The only issue I have so far is the electric trim is not working.   Any suggestions where to start troubleshooting?  Yes, the elevator trim switch was on.

 

 

[201er]

5 minutes ago, Papa K said:

Had my first flight in my M20J today.  The only issue I have so far is the electric trim is not working.   Any suggestions where to start troubleshooting?  Yes, the elevator trim switch was on.

Trifow into the yoke mounted trim switch. 

[Papa K]

13 minutes ago, 201er said:

Trifow into the yoke mounted trim switch. 

ok - like a contact cleaner spray to see if the switch is making good contact.  I'll try that.  Thanks

[EricJ]

A trick I had to learn was to push the button down to make it work.    This also disengages the autopilot on my airplane,  so it wasn't initially intuitive.    The airplane I was flying before just need the switch pushed forward or back,  so it was new to me to have to push it down as well. 

[Bolter]

Check the performance of your autopilot.  On my J (so I assume all of them) the electric trim is through the AP, whether the AP is engaged or not.  If you engage your AP and it is able to control pitch (you can see the trim wheel moving), then the problem is most likely your yoke switch and not something more drastic. 

FYI: Similarly, if you remove your AP for service, your electric trim will not work anymore.  

[ZuluZulu]

6 hours ago, Papa K said:

Had my first flight in my M20J today.  The only issue I have so far is the electric trim is not working.   Any suggestions where to start troubleshooting?  Yes, the elevator trim switch was on.

 

 

Which trim system do you have?

[Papa K]

5 hours ago, ZuluZulu said:

Which trim system do you have?

Good question - I don't know.  I figured it was factory.  There is a trim switch on the left side of the yoke.  Other than that, I will have to check the logs to see if there was a post-production trim put on.

[skykrawler]

Your absolute lack of knowledge will work against you.    There must be some documentation that came with your airplane.  A fundamental start would be what kind of autopilot is installed in your airplane?  Typically J models all have an autopilot.

[OR75]

4 hours ago, skykrawler said:

Your absolute lack of knowledge will work against you.    There must be some documentation that came with your airplane.  A fundamental start would be what kind of autopilot is installed in your airplane?  Typically J models all have an autopilot.

not said in the nicest way ... but i agree with you

[skykrawler]

5 hours ago, OR75 said:

not said in the nicest way ... but i agree with you

True, but this airplane is flying with discrepancy.  I apologize.

[Papa K]

11 hours ago, skykrawler said:

Your absolute lack of knowledge will work against you.    There must be some documentation that came with your airplane.  A fundamental start would be what kind of autopilot is installed in your airplane?  Typically J models all have an autopilot.

FYI - I've only owned it 2 weeks.  It is the first airplane I've ever owned.  That's why I'm here looking for help

Autopilot is original Century 21.

[BravoWhiskey]

In my case the trim had no lubrication and trim required excess torque which burned out the servo... had servo and AP repaired and trim adjusted and lubricated.

[carusoam]

Often…

The grease used to lube the trim system gets old… and needs to be cleaned out.

The grease used, has a tendency to get wiped and collect at the ends of the ‘usual’ range a particular pilot has…. Very much a WnB issue… load the plane a different way… and the trim may need to break through some old cruddy grease…

 

Old cruddy grease can turn into rocks… and pretty much make trimming a challenge…. There is a gear box in the system that may have decades old grease…

 

PP thoughts only, not a mechanic…

Best regards,

-a-

[1980Mooney]

 Did you see the comment above about pressing the rocker switch down while rocking it forwards or back? Pressing down energizes the trim.  I looked at your panel pics on Aircraft.com.  It looks like you have a yoke mounted switch like on my Century 41. 

Century 21 Manual

https://www.centuryflight.com/images/operating-manuals/68S805.pdf

Century 41 Manual
https://www.centuryflight.com/images/operating-manuals/CENT41.pdf
 

 

This description of the switch is from the Century 41 Manual.

Edited January 28, 2022 by 1980Mooney

[carusoam]

@Papa K check out the note above from 1980…

-a-

[1980Mooney]

5 hours ago, Papa K said:

FYI - I've only owned it 2 weeks.  It is the first airplane I've ever owned.  That's why I'm here looking for help

This may help you.

Service

mooney.free.fr/Manuels M20J/M20J/Mooney Service Manuel M20J Vol. 1 of 2.pdf

mooney.free.fr/Manuels M20J/M20J/Mooney Service Manuel M20J Vol. 2 of 2.pdf

Parts

mooney.free.fr/Manuels M20J/M20J/Mooney M20J Illustrated Parts Catalog.pdf

POH - 2 one older that matches your plane and one newer which has some additional and better presented information.

M20J-POH.pdf (nqac.com.au)

M20J_3203B (e-monsite.com)

[65C_flier]

On 1/27/2022 at 1:02 PM, EricJ said:

A trick I had to learn was to push the button down to make it work.    This also disengages the autopilot on my airplane,  so it wasn't initially intuitive.    The airplane I was flying before just need the switch pushed forward or back,  so it was new to me to have to push it down as well. 

+1. First flight after buying a 78J with Century III I thought the elec trim wasn't working until reading the Century Manual. After figuring out how to use it I decided it was too course and it annoyed me disconnecting the ROLL or HDG modes if I needed to trim. So now I just trim manually and leave the elec trim switch off. AP still works in all modes including ALT hold. Trim switch still disengages all AP modes.

Edited January 28, 2022 by 65C_flier

[Davo]

First posting on this forum. I just purchased a 1988 M20J. Electric trim went inop. 1 hour after taking possession during the flight home. Yoke switch appears to be working. KS-179 trim motor whirrs when switch selected but not turning the gear. Manual trim smooth and easy to adjust. First thoughts is shear pin or possibly a clutch? Anyone have experience troubleshooting this? Thanks in advance for your thoughts and sharing your experience.

Dave

[Steve Dawson]

I had the same issue when I owned my J. Before you start spending money on repairs, open the inspection door on the side and locate where servo to trim tube is. There's a chain connecting the two and it sometimes starts to seize or just needs lubrication. Or when its cold it will contract. Try spraying some lubrication on it and manually exercise the trim wheel and see if that helps. 

I think I spend a couple AMU's until I figured that out. 

[N201MKTurbo]

The trim servo has two circuits. One to run the motor and one to engage the clutch. It seems the clutch circuit isn’t working. I wouldn’t replace anything, I would find the broken wire or bad connection and fix it.