C1 tach jumps and screams

[don izzo]

Just finished my car (purchased in a basket) and find that the tach (which I thought I tested prior to installation)jumps around and makes an intermittant screaming sound so I disconnected it. At a local cruise the other night I met a fellow with another 1960 who said his did the same thing so he changed out the cable and it still did it. Then he sprayed WD40 into the cable at the generator end and reconnected it. He states after a short time the jumping and screaming went away and the tach now works great. I wonder if it's not caused by all of the extreme bends the cable takes in its route to the tach? How should I proceed with this, any ideas?

Don

[Bob Simard]

Re: C1 tach jumps and screams

On my 60, this was caused by the grease in the tach head drying out. I had the unit cleaned and regreased at a speedometer shop and it has been normal for several years. Good news, easy fix; bad news, the instrument cluster has to come out.

[Jack H.]

Re: C1 tach jumps and screams

You can check to see if it's the cable before you pull the instrument cluster.... Disconnect cable at both generator and tach end, the drive cable will slide out of the sheath. Clean 'er up and apply fresh lube (graphite is best in my book and small tubes of speedo lube are available at all auto parts stores). Re-insert freshly lubed cable into the sheath, reconnect and go for a test drive. If problem(s) evaporate, you did required maintenance before you 'lost' her!

[Ed Jennings]

Re: C1 tach jumps and screams

Frequently this problem is caused by lack of lube in the cable. Try removing the cable from the housing, throughly clean and relube. There is a special graphite based lube which is available at any parts store, but a lot of folks use ordinary grease. The inner cable comes out from the dash end, but you can probably get it out without removing the cluster. If there is a lot of dry lube in the housing it would be a good idea to run some spray parts cleaner through the housing as well to flush it out.

[don izzo]

Re: C1 tach jumps and screams

Thanks again for great info! it sounds like the guy at cruise night was right on with his suggestion that it is a lubrication problem. I'll attempt to remove the cable and clean and lube, you guys didn't address the question of the many bends in the cable. COuld it be you don't think this contributes to the problem?

Don

[Bob Simard]

Re: C1 tach jumps and screams

My speedo guy insisted that graphite lubes were abrasive on the cable and housing. He used (and strongly recommended) either GM's or Ford's speedo lube. This stuff is a grease and contains no graphite. Based on his comments, I would use chassis lube before I would use the auto center's graphite stuff.

[Ed Jennings]

Re: C1 tach jumps and screams

Don, so long as the cable isn't kinked the bends shouldn't be a concern. Obviously one wants to route the cable to minimize the sharp bends, but the system is designed with the bends in mind. Try the cable first, since it is much easier to correct. If that doesn't do the trick the tach itself may need attention.

[John H.]

Re: C1 tach jumps and screams

If you drive the car in cold weather, chassis grease isn't a good idea, as it gets pretty stiff at low temperature; stick with lubricants made specifically for speedo/tach cables. Corvette Central peddles such a lube called "Kable-Ease" that I've used for many years with good results; I've found that nearly all the repro speedo and tach cables I've bought arrived completely dry, with no lube at all - I pull the cable out of the sheath and lube them before installing them.

It's also an easy job to pull the gearbox off the back of the generator, open it up, clean everything, lube with gray moly lube, and put it back together; you'll probably find "cake" in it instead of lube.

[Craig S.]

Re: C1 tach jumps and screams

Bob - I wouldn't think graphite would be too abrasive for the cable and sheath, many folks have used it. However, I have had trouble at times with the graphite lube causing pulsing and bouncing on spedometers, which may have been related to my particualar cables. If there is any twist or flex in the cable itself, the graphite lube aggrevates this condition as there is no damping affect. Whenever I used the GM spedo cable lube, my problems went away, and it is actually a fairly gooey grease that adds some drag and controls pulsing. However, unlike regular grease, it is designed not to stiffen up at cold temperatures which would cause undue wear to the drive gears, eihter in the transmission for spedometers (plastic) or the steel cross gear in the tachometers. So I am a believer in the lube GM designed for this purpose. Maybe Joe Lucia knows the part number...Craig

[Mike E.]

Re: C1 tach jumps and screams

I've found the problem many more times to be the dried out lube in the head of the tachometer or speedometer than it is the cable. I've used tri-lube (tri-flow?) because it doesn't dry out as easily as WD-40 does.

[Theodore K.]

Re: C1 tach jumps and screams

Don,
I agree with Mike Ernst. The problem is often not the cable but the dried out grease in the head. I have developed a procedure to clean and relube using penetrating oil and vaseline. Did my speedometer on my 57 about 18 years ago and tach this spring and both are fine and steady and quite. The sceaming is probably the cable which is basically a spring getting wound up and then going super fast when it releases. This make the pointer jump as well. I wrote this up for the restorer but it has not been published yet. If you want a copy please send me an email and I will share with you.