Replaced the alternator - now the attitude indicator tumbles

[Kyle Wolfe]

OK, I'm perplexed. I had a draw showing on my ammeter. So my FBO checked and sure enough - a bad alternator. They replaced that. And from my review of posts on this site, I also told them to replace the tach drive seal while the alternator was off. They did that.

Went to fly tonight to check everything out. Immediately upon start up I noticed that my attitude indicator was tumbling. I had good/normal vacuum. I've got an O300D with a vacuum pump.

I didn't fly for fear of damaging the gyro. It continued to tumble. No way to cage or stop it - only a setting knob for the attitude reference.

I ran the a/c for a couple of minutes and shut it down.

I'll talk to my FBO tomorrow, but any ideas why the gyro keeps tumbling? I can't think of any tie in to the vacuum system and the alternator or tach drive seal. Any ideas here guys? Just an unlucky coincidence?

And I wish I was able to get to Reklaw!

[GAHorn]

As long as the alternator change-out didn't involve a forgotten vacuum pump hose clamp, etc. , .... there is unlikely a connection. (But I'm with you. Following any work, an unexpected failure is always suspect. Hope this isn't going to prevent you from coming to Reklaw! Operating the airplane with a gyro un-erected will not harm it if its a 3-1/8" pictoral gyro.)

[cessna170bdriver]

Kyle,

I would also guess it's a coincidence, but it's worthwhile to check all connectons on the back of the engine. If a loose hose fitting was the culprit, you should see a drop in your vacuum reading. Another possibility might be a dirty inlet filter. The vacuum gauge will read normal if the regulator is working (higher than normal if it's not), but you'll be getting insufficient air flow through the instruments.

If the vacuum reading is normal and the filter is OK, and the gyro is still tumbling, the gyro could be on its last legs. I have a 14-year-old RC Allen attitude gyro that oscillates fairly wildly in pitch and roll when it's cold outside, but otherwise works normally. I have a replacement gyro, and figure to replace it at next annual.

Miles

[Kyle Wolfe]

Thanks Miles and George for the replies.

Replaced the filter. No dice. Pulled the gyro and it appears that it failed. Am getting some options and prices for rebuild versus replacement.

No realationship to the alternator change. Guess I should have bought a lottery ticket last week as well!