The Tale of Nervous Tach Needle

[Jeff B.]

I thought I would share my recent quest for a stable tach needle on my 64 in the hopes that it may help someone else, or that I might learn something new from the responses.

During the restoration on my 64, I rebuilt the distributor complete with new main shaft and cross gear, and also had the tach rebuilt and replaced the cable. Still the tach had a bounce, actually more like a jitter of about 50 rpm at idle, but was probably not going to pass the PV. It was consistant in frequency and appeared to be the kind of problem associated with a cable. The cable was new, so I took it back off and lubed it with Cable-ease, but no change. I ordered a second cable, which I wanted to do anyway since I found one with the correct ivory colored sheath. I put that cable on and the jitter changed a bit but did not go away. I took everything back apart and inspected each component and even sent the tach out to be reinspected. Everyting looked great. I made sure the distributor was installed at the correct position, I tried tightening and loosening the cable attachment collars but again, no imporvement. So one evening I had the cable back out and was looking at it carefully. I noted that the small brass collar/stop that was crimped on the cable to retain/position it in the sheath was installed at the tach end of the cable. I could not find any information about which end of the cable it should be on but I had purchased two new cables and they had both shipped this way. So I just decided to pull the cable out of the sheath and insert it the other way so the collar was at the distributor end and ... you guessed it, problem solved and a perfectly stable tach. I assume that since the cable has a directional winding that the collar was being pushed up against the hub on the tach and causing friction. What I don't know is how it was from the factory. Anybody know the answer?

[John H.]

Re: The Tale of Nervous Tach Needle

What I don't know is how it was from the factory. Anybody know the answer?

Jeff -

The original tach cable (like the speedo cable) had the crimped stop collar at the tach head end.

[Jeff B.]

Re: The Tale of Nervous Tach Needle

I was afraid that would be the answer. I wonder if the manufacturers are crimping the stops on the correct end but have the cable directional spirals going the wrong way when the do it? Or crimping the stops in the wrong position so that it causes problems. I would sure like to have a NOS one to try out and compare. Meanwhile, mine is staying in with the stop at the distributor end - the only way it works correctly.

[Stuart F.]

Re: The Tale of Nervous Tach Needle

Very interesting. My 63 has always had a wiggle at idle - from day one. I have had it off several times and re-lubed it as just standard maintenance practice, but it's never changed. I'm so used to it that I'd be lost without it or fear something was wrong. Next time I disconnect it, I'll try changing it. My luck, after 47 years, it will break.

Stu fox

[Jeff B.]

Re: The Tale of Nervous Tach Needle

Well from what John H. says, the way I have it now is different from the stock NOS cable. But something is up here with the replacement cables at least. Truth be told, I actually tried three different cables because I wanted to try a different length as a solution, but reversing the cable in the sheath was the only thing that fixted. I noticed that when you insert the cable with the stop down and the distributor end, the cable itself bottoms out before the collar hits the distributor. And since the cable is supposidly wound so it pushes lube up, the force would be down on the cable. That would keep the cable in this position where the collar does not contact anyting. Like usual, I'm over thinking it but hey, it worked! And it WILL pass the PV, at least that part of the car anyway! Have a nice weekend.