69 tach problems
I'm having problems with the tach on my car. The needle bounces real bad ( I don't even think I can call it bounce) . On hard acceleration the tach needle will bounce radically ( between 1500 and 2500 rpm) usually between 2500 to 3500. It also bounces quite a bit when shifting but not as bad. The car has about 100 miles since a complete frame off resto. No parts were not restored or rebuilt. The tach and all other guages were restored by Roger Scott at corvette insturment service. The cable is new and lubed with no kinks or sharp bends. The distributor was completly gone through by Dave fiedler at TI specialties. I'm not sure how the tach mechanism works but am thinking the problem is in the tach. does any on e have any suggestions? Thanks for any input
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Re: 69 tach problems
Joe , when the tach "fails" it is like it looses its "connection" and rpm s fall and then its reconnected and starts working again but thats when the bouncing startsComment
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Re: 69 tach problems
I have seen a short cable do that, but most times its the speedometer head that needs service.Comment
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Re: 69 tach problems
Make sure that the cable is not kinked or the radius is to short near the distributor. They make a after market 90 degree bend if the radius is to tight. This is a common problem.Comment
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Re: 69 tach problems
One of the things that most folks don't know is that a pre-1975 Corvette tachometer, while being mechanical drive, is NOT DIRECT DRIVE. Mechanical direct drive tachometers are used for some racing applications but I don't know of any stock application for them. Consequently, a Corvette tachometer uses a damping mechanism and that's usually where this type of problem lies.In Appreciation of John HinckleyComment
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Re: 69 tach problems
joe, I know that the tach has some sort of "dampening" but not sure how it works. the rebuilder tried to explain it to me but I didn't really understand how it works. He said there is some sort of magnet arrangement . I'm just trying to rule out any other problems before pulling the dash out. I' sure you know what a pain that is. Thanks BradComment
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Re: 69 tach problems
If the distributor is properly installed following the directions in the shop manual, and the drive gear of the distributor is properly installed (no directions in any Chevrolet publication, but lots of posts here) the tachometer cable will be an almost straight shot into the IP grommet and into the tachometer. There is a difference in distributor orientation between midyears and C3s and if a mechanic who only knows C2s installs a C3 distributor you will have tachometer drive and other alignment issues. That 90-degree device was designed to solve these self-created problems. If the distributor is installed properly, that 90-degreee device is a solution looking for a problem.TerryComment
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Re: 69 tach problems
Brad, A couple of other things to look at, Is make sure the tach cable is attached correctly to the tach at the back of the dash, and I had a case where my tach cable had not been lubed, I removed the inner cable and lubed with some white lithium grease, this took care of my bouncing cable.New England chapter member, 63 Convert. 327/340- Chapter/Regional/national Top Flight, 72 coupe- chapter and regional Top Flight.Comment
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Re: 69 tach problems
Ed, pulled cable out of housing and greased it with speedo cable grease and had no improvements. As I said in original post its not really a bounce but a Huge jump. Thanks BradComment
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Re: 69 tach problems
Brad you mentioned in your post having a new tack cable. This may not be a problem solver, but the formed ends of the cable may not be making a firm enough fit to keep from losing their grip in a connection point. A electric drill that can turn both directions could be used on the distributor end of the new cable to test your tach for operation if the fit of the cable is questioned. I can't say which direction it will need to be turned.Comment
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