(‘68 427 L68)
Another tach issue popped up today. When I first got this car the tach worked when it wanted too and when it worked it just bounced around. Then eventually just went dead. I found that where the cable engaged the tach drive on the distributor it had been wallowed out/ stripped. A new cable and stainless tach drive got it working like new again. That was over a year ago. Now today I went to fire the car up and I noticed the tach not move for the first second or two the engine started but then it was normal. That was my only warning I had an issue. About 40 minutes into the drive the needle dropped dead, no bouncing, nothing. And there it stayed so I think its safe to say something just let go.
I haven’t done anything yet but my first diagnostic step will be to disconnect the cable from the tach drive on the distributor and hook a cordless drill to it to run in reverse. If the tach works that side is good and I’ll focus on the distributor end.
Ok, like I said, haven’t done that yet but I replaced the tach drive with an up graded stainless version and properly greased it. I also inspected the gear on the distributor shaft with a bore scope and the teeth were perfect. I’m inclined to to think in the way the tach failed this time it’s going to be the tach itself that went and its going to fail the drill test, what do you guys think ? Does this sound familiar to you ?

 

I think without even looking it could be anything. Those distributor gears are known to fail, cables can break. The tach itself can fail.
I think you need to have a look.

 

Use a drill motor to see if the tach needle moves. If you have to pull the dash, be smart have the tach along with the speedo Professionally Serviced. Removing and reinstalling the drivers dash was horrible, the worst repair that I have done on my 73.

 

If you’ve seen what I’ve done with this car, I’ve been thru repairing and rebuilding nearly every area of it.
Pulling the dash, again, doesn’t seem like much in comparison. One thing thats in my favor is that this doesn’t have A/C so theres fewer ducts in the way.
Not saying it won’t be involved but I’ve already replaced all the center gauges and radio having the center and right side out. Had the steering column apart as well. What I figured on doing is it is the tach itself I’d just replace the speedo (with cables) and tach together with ones from Zip. The odometer hasn’t worked since I’ve owned the car. I know I could just replace the odometer related parts but I figure my time is worth something so I don’t mind spending a little more to buy a new unit that I can install and be done with it. I had replaced all the gauge bulbs with new when I was in there last but they don’t seem bright enough so I might replace them with leds as well.

 

Lt.
Do you think the (most likely made) Chinese Tachs will work for more than six months? You could look for a NOS Tach on EBay, but the cost may be a little steep. The units are easily repaired, but I would only trust a shop that knows what they are doing. My local shop quit doing the mechanical gauges as the owner of the shop, is not working everyday. Unfortunately the young guys only want to work on the electronic gauges.

 

Ya I do, I get what your saying but where do you think all the parts are coming from when you send them out to a repair shop to be rebuilt… China.
So what’s the difference ? There are no secret stash’s of spare parts anymore for a 56 year old car. The gauges they sell are GM licensed so hopefully their quality control is a little better.
Getting them rebuilt gets the same Chinese parts but takes a longer turnaround time.
I’d rather have replacements in hand ready to go in so it’s all fresh in my head in how it all came out rather than wait a month to get them back and have to refer back to notes and pictures.
* A quick check of eBay has 2 Tachs both double the price and both low redline small block versions. Mine is the 5,600 redline version.

 

Ok, got my answer. The tach cable snapped. That cable was replaced last year so why ?
Maybe I shouldn’t think too much about it and be thankful its the least expensive thing to replace to make it right.
when I unscrewed the cable from the distributor the drive came out with it so I got to reinspect the gears and they look fine.
The drill confirmed the issue was on the cable and tach side so with the drill still attached I contorted myself under the dash, disconnected the cable and the cable turned, shouldn’t, then it pulled out slightly, shouldn’t do that either so I just pulled it out and came up with about 8” worth. Should be an easy fix.

 

Do you have the distributor correctly clocked to avoid stress on the cable. Chevrolet came out with a bulletin early in C3 production involving moving the wires in the cap one position and reclocking distributor.

 

Its not coming off it at an odd angle, I don’t know.
it was cold yesterday, thinking now I might have used the wrong grease on the cable when I installed it. Oops

 

There is specific speedo/tach cable lube – it appears to be a graphite suspended in a very low viscosity liquid carrier. If not replacing a cable, drip about a half dozen drops in the distributor end and the spinning of the cable will send it up the sheath toward the gauge. In your case, when you get the new cable ready to install, give the cable a coating and then remove any excess before sliding it in the sheath. If too much lube, it'll wind up inside the gauge mechanism and foul it.

 

That’s how I did it the first time. I don’t know how to explain this but maybe besides being a cheap $20 part maybe it’s cheaply made ????
I don’t know but at least it’s an easy repair.
fingers crossed it lasts longer this time around.

 

I have a dry graphite powder that I use...
Years ago it was called "Dry Slide", and I still have the same bottle my dad had from the 70's...
.I am not sure if it is still called that ...or if it is still available. But I am sure you can still get graphite powder...

 

We’ll now I’m waiting on a new cable to arrive and have been thinking, if I did use too much lube and the mechanism is fouled what should I do to correct it ?

 

Nothing at the moment, sure you don't want to remove the tachometer unless necessary

 

Yes, get a new cable first. Spin the cable with your finger tips before installation. Get a feel for it with zero load. Then after installing to the tach. Spin the distributor end of the cable with your finger tips. Does it feel like it spins freely without drag? No drag? All good. Feels sticky, binding? Oh ****.

 

You’ve got that right !

 

It’s raining today so I’m limited to what I can do on the various projects I have lined up. The cable is on the way so what I thought I’d do is to take a part of the broken cable and use it to spin the tach. I’ll do it like you say by hand first then with the drill in reverse. The cordless drill I have will only spin it to about 1,500rpm but it will show some life readings in the tach.
Gonna cross my fingers that it spins freely.

 

Update I installed a new cable and yes the tach itself spins easily. Instead of grease I used a little light oil. Firing it up it works as it should, but will it last ?
So I ordered a 90 degree adaptor to bring it away from the distributor in a smooth curve. Ok yesterday with it in hand I went to install it and its not going to work at all so I put it back together the way it was without the adaptor. Car runs great, tach works great but will it last this time ???
I’m going to hope the issue was the grease I used on the cable being too thick and freezing temps causing it to snap. If it does snap again it’s a $20 replacement and the last one lasted almost 2 years. This isn’t a perfect outcome but I’m just going to cross my fingers now with it and concentrate on bigger things like getting the wipers to work.

 

This is a great thread! I am converting mine back to the original distributor and this info will save me having to do this job twice. Original owner pulled the points out and went HEI and bent the ignition brackets to make room for the large cap.

Good luck with the wipers. Cheers

 

Do you have the distributor properly clocked? Chevrolet released a bulletin concerning the tach cable and repositioning the plug wires in the cap. Google for a paper by Lars Grimsrud on how to install the distributor and page down for the reclocking of the Corvette distributor.