The International Cessna 170 Association

My tach has been jumping all over, eventually wrapping all the way to max (about 4000 RPM probably) and making an awful noise when it's pegged..

I pulled out the inner cable, it came out just fine. Didn't see anything wrong with it, so we lubed it and put it back in. Same issue.

Replaced the tach with a new Mitchel yesterday, and it's also jumping all over the place at higher RPMS. So now I'm a bit stumped. AI wants to try a new cable.
Whats interesting is that at lower RPMS, both tachs seem to work, its higher RPMS where it gets jumpy.

make sure there isn’t any kinks in the outer cable or sharp bends . plus the square drive end is square. I had one once inner cable end wasn’t square and slipped at high RPM [jumpy] . Plus the inner part of the outer cable might have worn internally so it grabbing on the inner cable at high RPM.

BrianW wrote:My tach has been jumping all over, eventually wrapping all the way to max (about 4000 RPM probably) and making an awful noise when it's pegged..

I pulled out the inner cable, it came out just fine. Didn't see anything wrong with it, so we lubed it and put it back in. Same issue.

Replaced the tach with a new Mitchel yesterday, and it's also jumping all over the place at higher RPMS. So now I'm a bit stumped. AI wants to try a new cable.
Whats interesting is that at lower RPMS, both tachs seem to work, its higher RPMS where it gets jumpy.

Certainly sounds like cable issues.

Tach cables are directional either left lay or right lay depending on the direction of the Tach.
Have your A&P look at Spruce 10-16800 R or L as an example to see if you have the correct cable.