I have a 1975 tachometer in my BB restomod. I used it to get rid of the gear driven cable drive tach used up to 1974? When going thru the gears under hard acceleration, it is about useless because the needle flops up and down, bouncing until finally settling once I am near the top of the rpm near the shift point. Is this just part of using this tach or does some one have a fix?

It has an MSD distributor 8365, tach pick up single wire.
Has anyone tried the in line 10K ohm, 1/2 watt resistor?
08/27/2022, UPDATE, After traveling for a couple months to escape the cold weather and finishing up on multiple house repairs, I got back to the "hobby" car. I put an inline resistor (10K x 2). Shortened it, soldered 1/4" male and female spades on each end, covered it with shrink rap. It absolutely works. Steady as can be. I believe it eliminates the MSD coil interference. I am sure a tach filter would have worked also. Thanks for the suggestions and advice. Sorry if it was a "dumb" question to begin with. Didn't mean to frustrate anyone.

 

Was a new filter added when swapped? The filters were mounted to the top of the intake on 75 and up, just left of the dizzy.
Most likely though its probably the board on the back of the tach.

 

OMG I'm biting my tongue...

 

When the electric tach in my 77 went crazy, a number of years ago now. I first tried a new tach filter, cheap and easy.
But it did nothing. I got a new tach board from one of the vendors. The replacement boards are definitely a upgraded part. Yes you have to pull the whole bloody dash apart. put in the new board. And it's working fine to this day.
My money is on the board going out.
And no, it shouldn't bounce all over. And no I have never heard of putting a resistor in line with the tach.

 

wow what a great car and color...

OK .. I cannot speak to the MSD part.. BUT you have a PITA to get the tach out compared to my 79..
YMMV and if you want the cliff's notes version go to post 140...!!!!!!!!!!!!!!!!! thousands miles later still works PERFECT
https://www.corvetteforum.com/forums...uestion-2.html

 

Check your tach ground and the rest of your cluster grounds. Not sure how your 75 is but I know on my brothers 68 the ground attachment point on the drivers a-pillar/birdcage was definitely messed up. Basically in my case the ground from the OEM was a 1/4” sheet metal screw run into the steel of the birdcage/a-pillar. Of course this had worn the hole all stupid over the years and getting the screw tight without rounding off he hole out more was almost impossible. I’m sure this was causing an intermittent grounding issue at that connection and causing just calamity in general in the grounding. I fixed it by drilling the hole out and installing a steel rivnut in the a-pillar/birdcage. No more grounding issue there.

Also check your birdcage to frame ground. If this is wonky you can get some weird stuff too. In the case of my brothers car I found an area near the front of the cage that was exposed that we used as a new grounding point. I either drilled and buzzed a nut onto it with my welder or used another rivnut (not sure anymore). Drilled and welded a 1/4 square nut onto the gusset of one of the body mounts and connected the two with approximately a 12” ground strap from Napa. The clip on style ground IMO is just plain silly.

No ground issues and the tach (converted) is as steady as could be. Tach is fed by the MSD box in our case.