Technical mechanical tach comparison

Why are somany surprised !!! I am only in my late 40's , have Seen this since the mid 70's. There's a lot of factors that can lead to tach jumping around .

 

QUESTION
I have a Vertex and a minty Jones tach--I can spin the cable with a drill either direction and tach runs fine--and the Vertex has two outlets so cable can be spun both directions so DOES it matter which tach cable spot you use on the Vertex????

 

Like I said, it's not the needle bounce at idle that surprised me, that's normal. Its that the second tach reads 1000rpm low at 7000. THAT surprised me!

 

i never took one apart. do they work the same way a speedometer does?

 

SW tachs do. The Jones Motrola (Moroso) tachs are not magnetic.

 

any good speedo shop can remove and reinstall the bezel. I have had it done several times.

 

Starting about 1:50 thru 2:05 here.

 

I had a few that the cable was the cause ( needle bounce ) I use a drill while spinning,I moved inner cable in & out bending outer housing in diffrent shape's ,( no grease ) the cleand relube tach then read smooth off idle .
Over the yrs I have afew tach read different, Electric and mechanical Name brands ,
The one on my Flatty reads off above 2,700 & gain the higher it goes .