The International Cessna 170 Association

Replaced the trim cable pulleys in the aft section of the fuselage. Checked to make sure that the cables were not twisted by following them all the way to those pulleys. When working the trim wheel in one direction, the cables twist. When working it in the other direction, they untwist. What causes this and what is the fix. The concern of course is that they rub together which will result in premature failure.

Is this problem new? Have you recently replaced the entire system of cables..?? or have you replaced only the “pulleys”?

It’s difficult to understand exactly what you mean when you write “twist/untwist”. Do you men they wrap around each-other in a spiral..?? … or do you mean that each spins on itself as it travels back-and-forth…?

The former certainly should not occur if properly routed. The latter might occur if they were not (first operated) in a “relaxed” state when installed.

Did you clamp the limit-blocks before operating them back-and-forth ..?… thereby perhaps unintentionally placing a twisting-strain on the cables..? (Pay close attention to the installation of the limit-blocks as this is a tricky matter for some installers.)

(Also, Turnbuckle-ends at illustration 17 & 19 should not be allowed to twist as the tension on the cables are adjusted by the barrel (item 20). And the “swage-ball” within the “U”-clevis should accommodate any need to relax that side of the circuit…prior to taking-up the tension during installation. Friction will build-up on that “ball” as the cable-tension is brought-up to specification which will limit its’ rotaion-ability. If the cable is not relaxed prior to tension being finally “set” then any strain might result in a tendency to “twist” upon itself.

However, the two individual cable-circuits should NOT twist-around each-other. This would be a routing error. (and likely occurring during installation of those limit-blocks.) I discovered exactly this situation during a “pre-buy/annual inspection” of a 206 I once bought. It had apparently been operating with twisted trim cables for years.

Problem resolved. When I first inspected these cables, the cables rotated around each other as the trim was adjusted. One cable was actually over the other. I took the turnbuckle apart and rerouted the cables so that they were now parallel with each other. However, the pair still rotated as trim was being adjusted. Previous post suggested holding both ends as the turnbuckle was being tightened and that surely worked. Did that and now they run parallel with each other. Thanks for the input. And yes, I inspected the cables to make sure that the previous rubbing did not cause undue wear on the cables and they are ok.