Calling all Tach Guru's, Help !!!!

[Dan Owens]

Guys,

My tach is doing weird stuff. Works fine for days on end, then all of a sudden it dies and drops to zero. Sometimes it starts to drop in RPM on the dial but then comes back up again. Doesn't seem to matter what RPM or weather condition. It sometimes comes back on it's own. If I tap on the glass faceplate it pops back to life (everytime) and will work for seconds, mintues or days. The fact that I can tap on the gauge face and have it come back to life leads me to believe that it's in the gauge. Anything inside these things that need to be cleaned or adjusted? I've pulled the plug on the back and cleaned the contacts and put on dieelectric paste on but it still does it randomly. Shift light now works great though after not working for about two years!

[Dan Owens]

What no one have an opinion or smart ass comment on this? Guy's where's the love?

[Nitrometano]

May be can be a ground problem or bad contact problem.

[rotorhead]

I had weird tacho problems in my 88, it was due to a bad voltage regulator. The car's voltage was not being held to 13.5v and was varying as high as 22v under revs. The tach would bounce all over the place. It is easy to check just measure the voltage across the battery terminals with the engine running. It was a simple job to replace the regulator.

[POKDUB]

Dan,
I have my tach apart at the moment. The old circuit is bust, I have built a new one using an electronic breadboard and various components, so I have a reasonable knowledge about its heart.
From your description I would suspect either a broken internal connection, dry solder joint, or the needle movement is physically imparied somehow. I think a close visual inspection will identify the problem. Have a multimeter handy and check continuity

Depending on the model, taking the tach apart can be difficult. You may need to bend back half of the rim in order to disconnect the back housing. Take it easy.

[Lorenfb]

Send it to Pelican before it gets destroyed!

[scottb]

If Pelican can't help with a rebuild/repair, send it to North Hollywood Speedo.

[Dan Owens]

Okay Guys, Now that's the kind of love I'm talking about.

Thanks everyone for your input. Pokdub, thanks for your input too since you seem to be up to your eyeballs inside the thing. That's way past anything I'm capable of so it's off to someone else or find a new/used one.

Anybody got any idea what the comparison between rebuilding this one and finding a used one would be?