Trim travel question

[grbamford]

Gents,

I have noticed over the last few flights that it seems my trim gets stuck in a forward position in cruise. When I begin to trim aft for landing, it is almost as if it has stripped on the jack screw. After a number of turns it seems to catch up and trim normally. Any ideas?

Greg

[Jeff J]

The cable is likely slipping. There should be a tension adjuster on it somewhere. My PA20 had one above the headliner. My Cub has one in the tail just in front of the jackscrew. I couldn’t change the trim on he PA20 unless I slowed to 80-90 mph first until it was adjusted. Cable and/or pulleys could be worn as well.

[PA-16]

You may be able to just reach up put some pressure on the cable as you crank the handle to see if it is slipping, if it is it will grab once you put a little pressure on the cable.

[Stephen]

Every year at annual, I clean my jack screw, cable and pulleys. Then grease and oil. There is big difference. I would inspect it and clean it first.

[dgapilot]

Early airplanes have a single groove pulley system with an adjustable idler. Later ones have a dual groove pulley with a spring loaded idler.

The single groove system is subject to slipping if the pulleys get warn, the jackscrew is caked with old grease or if the cable gets oil.

You may have worn pulleys, dirty or warn jackscrew, or oil on the cable. Start by cleaning, then adjust the cable tension. If that doesn’t help, you will need to replace the pulleys. The system can be converted to the dual groove pulley system. Parts will run between $200-300, and there is welding involved, so best done during fuselage recover. You will need approved data to do it as there is no STC.


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[Steve Pierce]

Every year at annual, I clean my jack screw, cable and pulleys. Then grease and oil. There is big difference. I would inspect it and clean it first.

Ditto, no adjustment unless a Clipper or very early Pacer. The old grease gets hard in cold temps and the trim cable starts slipping on the pulling as it tries to turn.

[Gilbert Pierce]

After getting all the caked grease out of my jack screw many rears ago I have used nothing but PS2 to lubricate it. Have never had to clean it since. I squirt a little PS2 on every 3 months. I use white water proof Marine Lubriplate grease in the front and rear grease grease zerks.
It was converted to double groove pulleys in 04 with a new everything back there. No issues since.

[krwill]

After getting all the caked grease out of my jack screw many rears ago I have used nothing but PS2 to lubricate it. Have never had to clean it since. I squirt a little PS2 on every 3 months. I use white water proof Marine Lubriplate grease in the front and rear grease grease zerks.
It was converted to double groove pulleys in 04 with a new everything back there. No issues since.

This is just about what I did. Cleaned out the caked grease with break clean with a wire brush and greased with new. Still had problems. Cleaned it all again and sprayed with Corrosion-X, no problems. Every oil change I hit it with a couple sprays and so far so good.

-Ken

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