CRG Discussion Forum

Camaro Research Group Discussion => Maintenance => Topic started by: CantRepeat on September 03, 2021, 04:52:46 PM

Title: Tach accuracy
Post by: CantRepeat on September 03, 2021, 04:52:46 PM
I noticed that the factory tach in my 67 spins crazy numbers that I know aren't accurate. IE it will spin up to and past the 7k mark.

Is there anything to check or something to look at the fix the accuracy of the tach?
Title: Re: Tach accuracy
Post by: 69Z28-RS on September 03, 2021, 08:45:26 PM
GM installed factory tachs have NEVER been accurate...  which is why so many S-W tachs get installed when the driver cares...
Title: Re: Tach accuracy
Post by: CantRepeat on September 04, 2021, 10:07:59 AM
I can understand a couple hundred RPMs but but spinning up to 7k when it's probably closer to 4500 seems a bit much.
Title: Re: Tach accuracy
Post by: 69Z28-RS on September 04, 2021, 11:37:30 AM
they are bad about 'overshoot' in acceleration (revving), but are probably pretty accurate unless the rpms are changing rapidly... (ie. when driving at a constant speed in a gear)
Title: Re: Tach accuracy
Post by: Mike S on September 04, 2021, 02:40:55 PM
 Are you still using points or an aftermarket electronic ignition module? 
My 67 tach displays approximately 150 RPM's higher than what the engine is running at but its movement is smooth at all RPM's and using points.
Recently I had intermittent stalling and when it was running between stalls the tach would be bouncing and way off in RPM's vs. motor speed. I eventually found the cause to be a loose post nut on the coil that went to the points.

Mike

Title: Re: Tach accuracy
Post by: Stingr69 on September 05, 2021, 02:33:21 PM
You can have the tach repaired.  I sent mine to "Gary the Tachman" and it has worked fine for decades.   www.tachman.com
Title: Re: Tach accuracy
Post by: CantRepeat on September 06, 2021, 08:08:31 PM
Are you still using points or an aftermarket electronic ignition module? 
My 67 tach displays approximately 150 RPM's higher than what the engine is running at but its movement is smooth at all RPM's and using points.
Recently I had intermittent stalling and when it was running between stalls the tach would be bouncing and way off in RPM's vs. motor speed. I eventually found the cause to be a loose post nut on the coil that went to the points.

Mike

On the advise of a post here I switch to this breakerless ignition.

https://www.lectriclimited.com/breakerless-se-electronic-ignition-conversion

Seems to work rather well.
Title: Re: Tach accuracy
Post by: CantRepeat on September 06, 2021, 08:08:59 PM
You can have the tach repaired.  I sent mine to "Gary the Tachman" and it has worked fine for decades.   www.tachman.com

Thank you for the link. I might just send the tach off over the winter and get it checked out.