The Cessna 120-140 Association Forum

Need help, I'm missing something. With the jack screw fully retracted (as short as it can possibly get) and the push rod attached (elevator in neutral position), my trim tab is in the +2 deg position and upon jack screw full extension stops at +49 deg. No where near the +6 / -33. I have the travel, just not the right starting position. Can anyone provide the c/l to c/l of the pivot holes in the push rod. What am I missing. BTW the jack screw full travel is 1.50" @ 15 full turns and the push rod was laying in a box (unattached) when A/C was purchased. Thinking it has to be the wrong push rod.

It's difficult to measure as the forward rod end is inside the leading edge of the elevator. I'm estimating almost exactly 12".

You clearly have enough "travel" in the system to accommodate the proper range, it's just getting the proper range. If I was at your airplane and could see the trim tab, trim tab actuator, cable stops etc I could probably sort it out quick. If your rod length is off, then perhaps post some pictures.

I'll try to post some photos. My rod is 12" center to center. Jack screw is positioned correctly, I have not yet dropped the chain over the sprocket. I can get my finger in and spin the screw to draw the cyl back to the stop (flange bumps up against the cyl wall). I can get the same effect if I hold the gear still and spin the screw back where it protrudes from the stabilizer. Thanks for the help, will keep you posted

Out of curiosity, what position is the elevator in when you are making the measurements? IIRC, it needs to be faired with the horizontal stab.

Houston we have ignition! Started all over again, did not use the method in the club 140 maintenance book, started setting trim tab to full down limit (mechanically) and worked backward ... then I spotted what I had done. After rounding the last two pulleys I managed to flip the cable/chain 180 deg. Rotating trim wheel forward was lowering trim tab, not raising it (I was hitting the gear & jack screw stops). Had a heak of a time confirming rotation was back 180 and not forward another 180 (wrapping cables around each other) very hard to see/feel down in the stabilizer. Always figured the problem was me, I just couldn't see it at the time.

Are you saying the cables cross in the stabilizer? I recall they're supposed to cross in the tail cone. from there they should run straight, IIRC. The only reference I'm aware of is Figure 48 in the parts catalog. There are similar illustrations in Section 9 of the 100 Series Maintenance Manual.

My trim cables now look like the IPC. They don't really "cross" in the tail cone, the outboard cable rises at a faster rate so it goes around the top pulley. When looking down the tail cone they will look almost parallel (gently converging), from the side with X-ray vision: inboard cable to bottom pulley, outboard to the top pulley. I had managed to rotate the chain 180 between the last set of pulleys and the jack screw gear. Great idea to look at the IPC ... DUH. Beats the hell out of what "looks right". Sometimes we get ahead of ourselves, so it's good to hear another perspective. Thanks

6468 wrote: ↑Wed Oct 30, 2019 5:02 pm They don't really "cross" in the tail cone,

Yeah, you're right. They diverge from parallel, but don't actually cross.

First-time 140 owner here, going through my first annual inspection. Looking into the tail-cone, I see that the elevator trim cables cross as they run from under the battery box back to the pulleys at the rear-most bulkhead. Is this correct?

I think they are supposed to cross under the horizontal stabilizer, but It's been a long time since I actually laid eyes on that part of the plane.