Tachometer reading low?

KNS · 02-16-2005, 05:25 PM

I recently had my Tach looked at by North Hollywood Speedo. At the time my tach was reading a few hundred RPM lower than it should. NHS checked it out and said it was fine and that it was not uncommon for a Porsche tach to be a little off compared to actual engine RPM. I re-installed it and now it seems to rev slower and is also about 1000 RPM too low (70 mph is about 2500 RPM). I called them and they said to send it back and that they would have another look at it. Does this sound like a problem with the instrument itself or could it be something else?
Thanks.

clevy70911T · clevy70911T's Garage

Can't explain that, but mine sticks when I use defrost. I figure it heats up enough and something expands. I plan on taking apart and lubricating it.

KNS · 02-17-2005, 07:34 AM

Thanks for the reply. I asked North Hollywood about cold weather and "sticky" gearing. The man said that it's all electric, at least the later tachs. Nothing to lube.

RoninLB · 02-17-2005, 08:13 AM

mine is 100rpm slower througout the range. I believe there is a spring that gets weaker with old age?

clevy70911T · clevy70911T's Garage

No, there isnt any gears. I've been inside a tach and there is a metal circular piece the needle spins around to move. It could be lubed, but I'm not sure it will help either of us. My last tach stuck around 1500 rpm and would move past the spot if I tapped the tach face. I drilled a small hole and sprayed some lube in it. It didnt stick there anymore but was very sporadic. This time I'm going to be alittle more careful and lube just the moving parts rather than spray randomly

I'll try this before looking for a used tach.

I'll post a pic of the insides as soon as my camera battery is charged.

Quote:

Originally posted by KNS
Thanks for the reply. I asked North Hollywood about cold weather and "sticky" gearing. The man said that it's all electric, at least the later tachs. Nothing to lube.

clevy70911T · clevy70911T's Garage

Lubing the spindle might help. I wouldn't lube the metal disk whre contact occurs as it might add resistance and screw the signals from the copper coiled thingy. Sound like an expert, huh? hope this helps

KNS · 02-18-2005, 01:54 PM

Clevy,
Thanks for the photo, I see (I think) the spring that Ronin was talking about.

clevy70911T · clevy70911T's Garage

My tach drives me crazy. I just took on a road trip and it stuck with the heat going to the footwells only. I might try to insulate it from the heating ducts behind the dash. Any suggestions are welcome.