Normal Tach behavior?
Thread Starter
Burning Brakes
Joined: Jun 2003
Posts: 936
Likes: 3
From: Prattville, AL. My Dog Thinks I'm Cool!
Normal Tach behavior?
Can anyone tell me how a mid-year tach is supposed to act? My tach is steady at idle and under acceleration, but when I push in the clutch to shift, the tach needle jumps up then returns back to it's steady state. What gives? BTW I installed a new tach cable with my new mallory distributor. 
Thread Starter
Burning Brakes
Joined: Jun 2003
Posts: 936
Likes: 3
From: Prattville, AL. My Dog Thinks I'm Cool!
Originally Posted by KRUSIN2
The tach needle on my '65 does that too and has for MANY years, likely not a problem...
That's the answer I was looking for! 
The only reason I asked is my brother's 73' doesn't do that and my other Vette's are digital, so I didn't have anything to compare my 66' to. Thanks, Paul 
Last edited by pletner; Apr 17, 2006 at 05:57 AM.
Burning Brakes
Joined: Nov 2005
Posts: 924
Likes: 7
From: Northeast Ohio
Its called tach cable wind-up and it is not normal. At idle the tach cable rpm is obviously lower, at acceleration and at high speeds the internal resistance of the cable to the housing is creating enough friction that it is slowing the cables speed until it "winds-up" a bit and increases cable torque. Finally the cable breaks loose, the tach needle jumps and then settles back down only to start again. Lubricate the tach cable and look for any kinks, obstructions, dirt, etc. in the cable housing. Easy fix.
When it gets bad enough the break away force of the tach can snap off the needle pointer. New pointer are $40 plus time. I'd fix it before it causes more problems.
When it gets bad enough the break away force of the tach can snap off the needle pointer. New pointer are $40 plus time. I'd fix it before it causes more problems.
Thread Starter
Burning Brakes
Joined: Jun 2003
Posts: 936
Likes: 3
From: Prattville, AL. My Dog Thinks I'm Cool!
Originally Posted by SolidAxle
Its called tach cable wind-up and it is not normal. At idle the tach cable rpm is obviously lower, at acceleration and at high speeds the internal resistance of the cable to the housing is creating enough friction that it is slowing the cables speed until it "winds-up" a bit and increases cable torque. Finally the cable breaks loose, the tach needle jumps and then settles back down only to start again. Lubricate the tach cable and look for any kinks, obstructions, dirt, etc. in the cable housing. Easy fix.
When it gets bad enough the break away force of the tach can snap off the needle pointer. New pointer are $40 plus time. I'd fix it before it causes more problems.
When it gets bad enough the break away force of the tach can snap off the needle pointer. New pointer are $40 plus time. I'd fix it before it causes more problems.
