Factory Tach help... Does NOT go to ZERO why? HELP - The 1947 - Present Chevrolet & GMC Truck Message Board Network

72Levi · 12-22-2007, 05:54 PM

Hello All, I installed a factory used tach I bought on eBay and it does not go to zero WHY? The needle does not go to zero, I adjusted the calibration in the back but it still stays around 400 rpm when shut off. I have factory points and coil. I connected it to the negative side of the coil, it works fine except does not go to zero. I think the tach may be stuck or bad, any ideas anyone? I also connected it to 12v keyed on the fuse box.

**nightmare** · 12-22-2007, 06:47 PM

It's probably because there is no power going to it when the truck is off. My aftermarket one does that too. Doesn't bother me though. Does it go to 0 when you turn the key to the on position, but not started?

72Levi · 12-22-2007, 07:02 PM

No it does not go to zero with key on or off, with or without 12v just stays at 400 rpm, ugh! thanks for chiming in.

**nightmare** · 12-23-2007, 02:36 AM

Well shoot, I don't know then. Maybe the tach isn't properly grounded? I'm just throwing out a suggestion.

Here's a bump for ya though, in case someone else has any ideas.

Huck · 12-23-2007, 03:37 AM

the original factory tach's came in at least 4 design's but the common issue is that they are electromechanical based on magnetic pulse. There is a cardboard tube like cover with some foam tape that is supposed to keep the inners clean. You may have some of the foam holding back the needle. You can take it apart to check it out. Just don't get to crazy with it as you can also really break it in the process.

Slammed70 · 12-23-2007, 02:58 PM

Quote:

Originally Posted by 72Levi

No it does not go to zero with key on or off, with or without 12v just stays at 400 rpm, ugh! thanks for chiming in.

Does it even work?

**Bob B.** · 12-24-2007, 12:03 AM

My tach did go to zero when you turned the engine off, but after I had it calibrated it doesn't quite go all the way to zero. I don't care, I would rather have an accurate tach!

12-22-2007, 05:54 PM	#1
72Levi Active Member Join Date: Feb 2006 Location: sa tx Posts: 851	Factory Tach help... Does NOT go to ZERO why? HELP Hello All, I installed a factory used tach I bought on eBay and it does not go to zero WHY? The needle does not go to zero, I adjusted the calibration in the back but it still stays around 400 rpm when shut off. I have factory points and coil. I connected it to the negative side of the coil, it works fine except does not go to zero. I think the tach may be stuck or bad, any ideas anyone? I also connected it to 12v keyed on the fuse box. __________________ 1972 K5 Blazer ALL ORIGINAL paint & engine, A/C, Tilt, 4sp, AM/FM, Tow Hooks, Aux Battery Tray, Tach, Vacuum 2004 FORD FX4 SuperCrew 2005 CTS-V 12 sec family car 2008 Buick Enclave AWD, Nav, & DVD, Wife LOVES it! Last edited by 72Levi; 12-22-2007 at 05:55 PM.

12-22-2007, 07:02 PM	#3
72Levi Active Member Join Date: Feb 2006 Location: sa tx Posts: 851	Re: Factory Tach help... Does NOT go to ZERO why? HELP No it does not go to zero with key on or off, with or without 12v just stays at 400 rpm, ugh! thanks for chiming in. __________________ 1972 K5 Blazer ALL ORIGINAL paint & engine, A/C, Tilt, 4sp, AM/FM, Tow Hooks, Aux Battery Tray, Tach, Vacuum 2004 FORD FX4 SuperCrew 2005 CTS-V 12 sec family car 2008 Buick Enclave AWD, Nav, & DVD, Wife LOVES it! Last edited by 72Levi; 12-22-2007 at 07:03 PM.

12-23-2007, 03:37 AM	#5
Huck Senior Member Join Date: Jun 2001 Location: Shelbyville, KY Posts: 3,261	Re: Factory Tach help... Does NOT go to ZERO why? HELP the original factory tach's came in at least 4 design's but the common issue is that they are electromechanical based on magnetic pulse. There is a cardboard tube like cover with some foam tape that is supposed to keep the inners clean. You may have some of the foam holding back the needle. You can take it apart to check it out. Just don't get to crazy with it as you can also really break it in the process.

12-24-2007, 12:03 AM	#7
Bob B. Senior Member Join Date: Aug 2005 Location: Los Angeles Posts: 1,369	Re: Factory Tach help... Does NOT go to ZERO why? HELP My tach did go to zero when you turned the engine off, but after I had it calibrated it doesn't quite go all the way to zero. I don't care, I would rather have an accurate tach! __________________ 1967 GMC CM-2500 Camper Cruiser, 351E V-6, NP 435 4 speed, Dana 60, and factory A/C. 2012 GMC K-3500 WT regular cab, 6.0L Vortec, 6L90.

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