Noisy tach cable - or is it the tach that is noisy?

[California]

I am gradually cleaning up some minor neglected stuff on the YM186D I bought last summer.

The tach cable sounded noisy when I bought it, and the tach needle was jumpy. The cable core looked well oiled so I rubbed it down with a paraffin block. That quieted it for a while. Now there is jarring whine for a moment when I start. I thought the starter might be failing to disengage but then I noticed the tach needle is jumpy again.

I found that the noise is sensitive to where the tach cable is routed. If I could tie it down in just the right location it would stay quiet. But moving it causes the screech and jumpy tach. It seems the racket comes back whenever the cable pushes sideways (or inward?) where it enters the tach. The screech sounds like stripped gears in the tach, and the needle stays past maximum rpm.

Has anyone seen this? Was it the cable, or the tachometer?

Replacing the tachometer cable looks easy but doing the tach would mean removing the steering wheel and dashboard, probably an afternoon project.

 

[kenmac]

When my tach went bad.There was never a noise . The gears would hang up & break the cable..I was sent a new tach ( warranty) no more broken cables.

 

[Roonabeck]

Has anyone seen this? Was it the cable, or the tachometer?

Well, on my Nissan 280zx, I once had a similar symptom with the speedometer. It was jumpy and would tend to peg itself against the maximum reading, and made a scraping/grinding noise. It eventually broke off the indicator needle, so I got a junkyard replacement speedo and took the old one apart one day. The way it worked was there was a magnet that the speedo cable would spin, and there was a similar magnet attached to the needle. When the speedo cable magnet spun, it would try to spin the speedo needle magnet (and the speedo needle would push against a spring). Cable turns faster and MPH reads higher. What happened in my case was something wore down and the two magnets started rubbing against each other inside the speedo. That imparted a lot more force against the needle's magnet than it was designed for, and caused the needle to hit the little stop post on the gauge display and eventually break off.

I don't know how the tach on the 186d is designed, but I imagine it could develop a similar problem. If you disconnected the tach cable from the tach and the noise stopped, I think that would point to the tach itself as the problem.

 

[California]

I think it is the same design tach that you described. And your explanation matches my experience. The racket and pegged needle begin when the tach cable is misaligned. So it seems the tach is worn or rusty inside, making the magnets scrape.

Today with the cable zip-tied in a straight line coming from the tach it worked correctly. So for the moment I'll put up with it because pulling the dashboard on a YM186 looks non-trivial. I wish this thing were as simple as my YM240! It has all that stuff accessible.

Does anyone have a good used tachometer they would like to sell?