Trim "sticking"

[N201MKTurbo]

15 hours ago, Bartman said:

I've been having a problem with trim as well and appreciate the wealth of information on this board. I think mine is the electric trim switch, and it is intermittent both in flight and on the ground. Trim wheel works fine so I have been keeping my hand on the wheel and if it doesn't work electric then I use the manual trim wheel. 

After looking at all of those GREAT step by step instructions and photos above we are going to clean the switch and do the jack screw too. 

Thanks again to N201MKTurbo and 1524J

My Century electric trim was intermittent because of bad connections on the connector that goes into the disconnect relay. Crawl  under the panel and bend the wiring around on the disconnect relay while actuating the electric trim and see if you can localize the intermittency.

On my 77 the relay is on the firewall by the vacuum regulator.

Edited May 30, 2016 by N201MKTurbo

[Bartman]

I have the Century IIB with add-on System 30 for pitch axis. Both have disconnect on the throttle quadrant and no disconnect on the yoke or on the trim switch, just on the console toggle switches.  I figure the trim rocker switch is low voltage and activates a relay to the trim motor so all connections and are suspect.  I'll also look to see if there is something going to the disconnect. I figure we need to spray the switch well with contact cleaner and check/clean all connections.  I have the wiring schematics in the hangar so we should be able to track it down. 

Thanks for all the info !

[N201MKTurbo]

In my case it wasn't the switch it was the wiring to the disconnect relay. The relay is in a two inch square golden (alodyned) box usually mounted to the firewall.

I have had all kinds of problems with that relay! I've had the contacts go bad and had to burnish them to get them working, The coil form melted from the Arizona heat and jammed the armature. The internal wiring has fractured and needed to be repaired. The wiring in the connector that connects to the relay has fractured and needed to be repaired.

That relay has all the high current signals for the roll servo and the trim servo running through it. Both the motor drive and engagement solenoid power go through it. That is a lot of power going through that tiny little connector.

[Guitarmaster]

On May 28, 2016 at 0:02 PM, 1524J said:

N201MKTURBO has graciously allowed me to use his instructions and I thought I would add some pics and observations of my own when removing the jackscrew in the tail cone for cleaning.

Run the trim to the nose up stop. Remove the sheet metal that covers the tail gap and the tail inspection plates. Measure the gap at the bottom of the tail and write it down. Take apart the universal joint just aft of the trim wheel.

You'll need to pull the Clevis pins in the pics. Make sure to have new cotter pins when reinstalling. 

There is a inch and a half collar inside the tube with double pins. On mine the ordination of the holes in the collar and tube had to be reinstalled as removed. In other words, if you spin the interior collar 180 degrees, the Clevis pins will not fit. Not hard to remedy, but can a little frustrating until realized.

This is where you measure the distance between the hinge points. The picture is after reinstallation so your measurement will be different.

 

 

Out of an abundance of caution I also marked my verticle stabilizer with a straight egde laying flat on the dorsal fins. You don't want to lose trim orientation.

 Slide then torque tube forward until the square coupling on the jack screw comes apart.

Remove the trim link in the tail gap. This bolt is hidden under the boot. Just pull it back and you'll have access.

 Remove the boot. Remove the two bolts that hold in the jackscrew, they are at the four access holes in the sheet metal.

Once the bolts are removed, you can now remove the jackscrew. It's takes a little work to get the jackscrew out, push down slightly and it'll come out but take it slow. Also, maintain the orientation of the jackscrew. I keep a shop rag handy and marked the top of the main block and both plates on either side with a sharpie. As  N201MKTURBO states, there are very thin shims inside the jackscrew. Don't forget them when you reassemble. 

Double check to make sure your trim is at the same point as when you started by checking your tail cone distance and/or verticle stabilizer. 

As always, get your A&P's blessing before starting and have them check your work.

 

 

 

We DID lose the trim orientation.  It's not a big deal to adjust.  We got it close, flew it, noted the trim position, landed, adjusted and all is well.

As a follow-up, the trim rolls smoothly now.

[Bartman]

FYI

We did spray the trim rocker switch very well with the electrical cleaner.  I don't know how other switches work, but with mine you simultaneously push down to engage, and also must push forward for UP and backward for DOWN trim.  After spraying well and working the switch in all possible combinations there is both a change both on the ground and in the air.  

Prior to spraying with the electrical cleaner I do not remember hearing any noise on the ground.  Now I can hear a relay engage when I push the switch down to the engage position even before pushing for UP or pulling back for DOWN.  We have flown several hours and I have had no further issues with the trim switch.

However, on the ground I can hear the trim motor is not working smoothly through its travel, and at certain positions in its travel it is obviously working harder than at other times. It is not binding up or anything like that so at next annual we will disassemble and clean the entire mechanism as detailed above.