Tachometer quandry

[Paul71LT1]

I have a '73 coupe that I picked up for a good price with a non-running and unknown engine. It was not running because it sat for 10 years before I bought it. Well I got it running with only a carb (Q-jet) rebuild and new plugs. The carb number matched up to a '79 and the block casting number matches to a 2 bolt main, 400 SB, made between '70 and '80. The presence of the HEI distributor supports the '79 vintage. The issue is that I do not have a functioning tach. My options appear to be to replace the tach with a '75 model, replace the distributor with a '74 or earlier and give up the HEI, or buy an aftermarket electronic ignition with a tack drive. I listed the options from least to most expensive. The car is definitely in the "driver" category so originality does not matter. I have to take the dash apart this winter anyway so the tach swap won't be much more and at $100 for a used one it is certainly the cheap way out, yet I like a mechanical tach for its' responsiveness. I'd like to hear the thoughts of any of you out there who may have some experience in this area.

 

[Robin7TFour]

i have an electronic 75 tach in mine. once i had a filter made for it the sweep was perfect works great!

 

[72VETTE454]

I have a '72 with a gear driven tach, which bounces a lot and drives me nuts. I am told that this is not normal and I may need a new tach drive gear. I replaced my points with an aftermarket Mallory Unilite conversin kit, which was $100, easy to install and works great. I don't know if any of that helps, but that is my story. If I were you, I would go with the newer tach option, mainly to get away from moving parts. Good luck.

 

[resto75]

Robin,

What was your tach doing before the filter was installed. Mine works but reads higher than it should. I was wondering about the tach filter. I don't think I even have one.

 

[Paul71LT1]

Everything I've read on the subject suggests that running without the electronic filter raises the risk of burning out the board in the tach, but it should still be accurate if properly calibrated. Regarding the bouncing mechanical tach of 72VETTE454, that is caused by a sticky drive cable. It's common with speedometers too and they can usually be fixed by cleaning and lubricating. The tach cable has the added problem of a rather tight bend radius which may be causing the sticking. Angle drives are available to eliminate the bend. Try disconnecting it at the dist. end and pulling out the cable to clean and lubricate. I doubt the is anything wrong with the drive gear.