M20J very hard to trim nose up

[Skywalker]

Has anyone had problems with the M20J trim system being very difficult to trim nose up? My electric trim bit the dust, probably because it was working too hard to accomplish the nose up trim. Now that I've had to do it manually, I realized how hard it is to move the trim wheel.  I've had my mechanic tear the whole system apart, starting at the tail and working his way to the trim wheel. He couldn't find anything really wrong with it. He spent over a week looking at every component, cleaning, etc.. Can't really find any thing wrong, and can't seem to make it more than marginally better.

Any help out there?

thanks!

[N201MKTurbo]

8 minutes ago, Skywalker said:

Has anyone had problems with the M20J trim system being very difficult to trim nose up? My electric trim bit the dust, probably because it was working too hard to accomplish the nose up trim. Now that I've had to do it manually, I realized how hard it is to move the trim wheel.  I've had my mechanic tear the whole system apart, starting at the tail and working his way to the trim wheel. He couldn't find anything really wrong with it. He spent over a week looking at every component, cleaning, etc.. Can't really find any thing wrong, and can't seem to make it more than marginally better.

Any help out there?

thanks!

You should service your trim jack screw. You have to remove it from the plane, disassemble it, clean it and regrease it. It should be done every 30 years or so….

[MikeOH]

Yuuup.  The jack-screw needs a thorough clean and re-grease.  That fixed mine.

[Ragsf15e]

As the other two guys said, just needs cleaning and new grease.  There are lots of threads on the same issue.

Other possibilities, there’s a “friction screw” on some models it’s sideways into the manual trim wheel if I remember right.  It could also be old / hard grease in the chain assembly directly underneath the manual wheel (in the belly).

[Skywalker]

Yep have already cleaned and greased the jack screw. Didn't help.

“friction screw” on some models it’s sideways into the manual trim wheel .." - yes we looked at that screw also, but can't seem to make it any better. Can't find a replacement assembly either. Any ideas on that?

Anyone know anything about the two coil tension springs in the empennage? Those seem to be geared to help with nose down trim, but we're not really sure if they impact nose up?

 

[MikeOH]

Well, that is odd.  I'm not an A&P, no idea about those springs.  My only thought is something is mis-aligned and is causing binding.  Maybe have your A&P start to isolate parts of the system by disconnecting U-joints?

[PT20J]

Hard to tell how stiff you are talking about. Is it stiff in the air as well as on the ground? It's normal for it to take more force to trim nose up on the ground because you are lifting the whole empennage against gravity with the trim system. 

[Skywalker]

2 minutes ago, PT20J said:

Hard to tell how stiff you are talking about. Is it stiff in the air as well as on the ground? It's normal for it to take more force to trim nose up on the ground because you are lifting the whole empennage against gravity with the trim system. 

No it's not within normal tolerance stiff. It's dangerous if in IFR on approach trying to move it. Very difficult. Yes both on the ground and in the air, more so in the air with a load.

[PT20J]

1 minute ago, Skywalker said:

No it's not within normal tolerance stiff. It's dangerous if in IFR on approach trying to move it. Very difficult. Yes both on the ground and in the air, more so in the air with a load.

What electric trim do you have? 

[Skywalker]

I think the electric trim was original. I just had it replaced with the Garmin electric trim kit that goes with the 500 autopilot that I already had installed.

[Ragsf15e]

12 minutes ago, Skywalker said:

I think the electric trim was original. I just had it replaced with the Garmin electric trim kit that goes with the 500 autopilot that I already had installed.

Have you taken apart the chain assembly and turned the jackscrew by hand to see which part is binding- chain/wheel or screw?

[Skywalker]

34 minutes ago, Ragsf15e said:

Have you taken apart the chain assembly and turned the jackscrew by hand to see which part is binding- chain/wheel or screw?

Yep did all that.  We even added resistance and turned everything by hand. Could not identify any rough/sticky spots.  Our current thinking is the only solution is new parts to prove what is working and what isn't, but we can't find any....  There are some parts on eBay but they are even older than mine!

[EricJ]

You can disconnect the control shaft at one of several places, which will let you determine which side of the connection the binding/stiffness is happening.   That'll help isolate it to the trim wheel/box or the jackscrew, or whether the rod is binding in one of the passages or perhaps one of the u-joints has failed.

When you disconnect it just mark everything's position so that it goes back together in the same position that it came apart.   Running it to one end of the travel can make that easier.

 

[Skywalker]

36 minutes ago, EricJ said:

You can disconnect the control shaft at one of several places, which will let you determine which side of the connection the binding/stiffness is happening.   That'll help isolate it to the trim wheel/box or the jackscrew, or whether the rod is binding in one of the passages or perhaps one of the u-joints has failed.

When you disconnect it just mark everything's position so that it goes back together in the same position that it came apart.   Running it to one end of the travel can make that easier.

 

Yep we've done that too. When you disconnect the drive train to isolate the ends the wheel end isn’t a problem and the aft end jack screw still has resistance but the wheel end has no mechanical advantage and thus trim nose down not too bad but nose up very hard.

We are thinking it could be those coil tension springs in the empennage, but can't really figure out their purpose. Any idea on that?

[PT20J]

8 hours ago, Skywalker said:

We are thinking it could be those coil tension springs in the empennage, but can't really figure out their purpose. Any idea on that?

Those are trim assist bungees. When you move the trim wheel, you are moving the entire empennage to change the angle of incidence of the horizontal stabilizer. But, the bungees also move the stick-free center point of the elevator when the trim moves. This removes some stick force in flight so that the stabilizer doesn’t have to move as much to trim out all the stick force.

[PT20J]

11 hours ago, Skywalker said:

I think the electric trim was original. I just had it replaced with the Garmin electric trim kit that goes with the 500 autopilot that I already had installed.

Whoever installed the GFC 500 trim should have checked out the trim system. There is a spec on max. run time stop to stop. The Garmin trim servo is geared up to meet the spec and this reduces the available torque at the trim shaft. If there is much friction in the trim system, it will not meet the run time spec.

10 hours ago, Skywalker said:

Our current thinking is the only solution is new parts to prove what is working and what isn't, but we can't find any....  There are some parts on eBay but they are even older than mine!

Randomly throwing used parts at it is not a good solution. It doesn't seem that your mechanic is very familiar with Mooneys. If I were you, I would take this to a Mooney Service Center where there are mechanics that are very familiar with Mooney trim systems. There is a list of MSCs on Mooney.com.

[skykrawler]

Disconnect the jackscrew at the point it attaches to the  empennage - just above the hinge.  There is a procedure for this where a block of wood is placed to support the tail.    Having done this, verify that the tail moves freely without binding.  It will be heavy to pivot upwards.    With the jackscrew disconnected in this way you can determine if there is resistances in the system without the tail weight contribution.

Personally I think the machining for the jackscrew and nut is not the greatest and it carries a heavy load.  Some of the jackscrew assemblies have caged ball bearings, others have tapered bearings.   The pre-load on the tapered bearings seems to be set by the thickness of the gasket.

You should mention what year your airplane is - it can make a difference.

[EricJ]

10 hours ago, Skywalker said:

We are thinking it could be those coil tension springs in the empennage, but can't really figure out their purpose. Any idea on that?

Those are supposed to be there.   They're why your elevator doesn't droop when you're on the ground.    When you the trim all the way up, the elevators should bias up a bit more, and when you run the trim all the way down the elevators will droop more.    Those springs are what do that and they're supposed to do that.

[Skywalker]

4 hours ago, PT20J said:

Whoever installed the GFC 500 trim should have checked out the trim system. There is a spec on max. run time stop to stop. The Garmin trim servo is geared up to meet the spec and this reduces the available torque at the trim shaft. If there is much friction in the trim system, it will not meet the run time spec.

There is a long list of errors by the original installer which we are fixing now.  I wouldn't be surprised if this step was short cut too.

Airplane is 1977. Year one of the J model.

Thank you everyone for the ideas, appreciate all.

Edited July 9 by Skywalker

[EricJ]

28 minutes ago, Skywalker said:

Airplane is 1977. Year one of the J model.

That's the best year for a J.    And a J is the best Mooney, so...   

 

[Skywalker]

14 minutes ago, EricJ said:

That's the best year for a J.    And a J is the best Mooney, so...   

 

Agree 100% !! Best fuel / performance /payload ratio of the bunch. And the only year with a real throttle.

[201Steve]

I also have a 77 J (the best J as has been said). My trim system was pretty stiff, everything seemed fine like you said, we replaced the rear jack screw. It made it a lot better but it’s still kinda stiff. 
 

it was a new part from Mooney. 

[Fritz1]

Put Triflo into the tail pivot bearing, the entire tail pivots around that bearing, think 5/16" bolts

[RangerM20]

On most models with electric trim, there is a motor chain driving a sprocket on the trim shaft.  On the bracket that holds the whole assembly, there is a bronze bearing supporting the trim shaft.  If that bearing is not exactly in line with the shaft, it can be very difficult to move the trim wheel.  There are several screws and nuts on the support assembly to move the support around to accomplish this.  If nothing else works, you can loosen these up and move them around to where the trim is easy to move.

[Skywalker]

Thank you!