Lazy Tachometer

[59diamond]

Recently when I first start up my 60 Bugeye the Tach just sits at zero. After I warm up the car it begins to move and acts normally. It is only when the car has sat for a few days that this happens. WhenI drive it around and stop and start the car it doesn't do this. Anybody have any ideas about this?

 

[David_Doan]

That's a mechanical tach that is magnetically coupled. The spring-loaded needle mechanism is sticking. A shot of WD-40 or similar in the hole where the gauge lamp mounts might free it up. Otherwise, take it apart and clean/lube

 

[59diamond]

So I unscrew the tach cable and shoot a little WD40 into the back of the gauge where the tach cable mounts up. That makes sense. What doesn't make sense is if the tach cable is spinning why would the dial not spin right away since it is connected to the cable.

 

[Jim_Gruber]

And Bill didn't you just have this fixed a few months ago? Can you elaborate on what got fixed so folks understand the previous issue.

 

[BustedKnuckles]

What doesn't make sense is if the tach cable is spinning why would the dial not spin right away since it is connected to the cable.

I'm guessing that the tach cable is connected to a magnet that spins inside a cup that the tach indicator is connected to. There may not be any solid connection between the cable and the indicator.

 

[David_Doan]

So I unscrew the tach cable and shoot a little WD40 into the back of the gauge where the tach cable mounts up. That makes sense. What doesn't make sense is if the tach cable is spinning why would the dial not spin right away since it is connected to the cable.

No, pull out the lamp socket at the top of the back and shoot some lube in towards the center. The tach cable is not directly coupled to the needle. The tach cable turns a magnet. The needle is attached to a metal cup that the magnet spins in. In your case it sounds like the needle assembly is binding slightly when completely cold.

A few pics below to help:

 

[59diamond]

Sorry Jim to confuse you. The problem I had before was with my 59 BE, 59 Diamond this problem is with 60 Frog. Shooting some WD-40 through the lamp socket should be easy to do.
Thanks for the Info David.

 

[59diamond]

I shot it with WD-40 through the light bulb socket. It is working correctly now. I am going to wait until tomorrow morning when it is cold and see what happens then.

 

[dklawson]

This is your gauge and your choice of how to service it.

Personally... I would not spray any oil inside a mechanical speedo or tach. The spindle that supports the pointer is supported on the inboard end by a needle bearing. That bearing is supposed to be clean and operate dry. Any lube, even WD-40, will increase the drag on the spindle coupling it "more" to the magnet assembly. This means initially the gauge will read high. As the oil collects dirt and thickens with age you may find that one day the pointer goes all the way around the gauge face and an autopsy will reveal the return hairspring has been twisted into a knot.

You can Google for the 27 page PDF by Anthony Rhodes that discusses cleaning and calibrating Jaeger and Smiths speedometers. The mechanical tachs are the same as speedometers except for their lack of odometer components. The PDF will walk you through how to clean and recondition your gauge.

 

[David_Doan]

This is your gauge and your choice of how to service it.

Personally... I would not spray any oil inside a mechanical speedo or tach. The spindle that supports the pointer is supported on the inboard end by a needle bearing. That bearing is supposed to be clean and operate dry. Any lube, even WD-40, will increase the drag on the spindle coupling it "more" to the magnet assembly. This means initially the gauge will read high. As the oil collects dirt and thickens with age you may find that one day the pointer goes all the way around the gauge face and an autopsy will reveal the return hairspring has been twisted into a knot.

You can Google for the 27 page PDF by Anthony Rhodes that discusses cleaning and calibrating Jaeger and Smiths speedometers. The mechanical tachs are the same as speedometers except for their lack of odometer components. The PDF will walk you through how to clean and recondition your gauge.

There are degrees of right and wrong... His tach clearly already has issues and probably needs an overhaul. A little light weight lube like WD-40 - which also evaporates - is pretty low risk.

One of the challenges of giving advise on forums is that you don't really know the skill set of the OP. I'm sure if you handed a tach and Rhodes' document to 10 random guys on this forum, not all 10 would return with a working tach.

 

[dklawson]

As I said, it's your instrument. Service it as you see fit.

 

[59diamond]

I appreciate everything both of you are saying. I fall in the category of a limited skill set. That is why I asked the question on the Forum. All of my gauges are in good condition and were restored recently. I do have access to people who know what they are doing and I rely on those people when I have mechanical problems. I am aware of the return hairspring in the tach since I buggered up the tach on my 59 BE by using the wrong lubricant.The tach is now working fine. As an aside I originally asked Jim Gruber what I should do and he said I should put it on the Forum and see what answers I got. Davids answer worked and was not a severe solution in my opinion. I don't restore cars I just try to maintain them in good order for my driving pleasure.

 

[David_Doan]

I'm happy it worked for you. If it happens again, I would take it back to the guys that rebuilt it.

 

[Deleted member 8987]

This is your gauge and your choice of how to service it.

Personally... I would not spray any oil inside a mechanical speedo or tach. The spindle that supports the pointer is supported on the inboard end by a needle bearing. That bearing is supposed to be clean and operate dry. Any lube, even WD-40, will increase the drag on the spindle coupling it "more" to the magnet assembly. This means initially the gauge will read high. As the oil collects dirt and thickens with age you may find that one day the pointer goes all the way around the gauge face and an autopsy will reveal the return hairspring has been twisted into a knot.

You can Google for the 27 page PDF by Anthony Rhodes that discusses cleaning and calibrating Jaeger and Smiths speedometers. The mechanical tachs are the same as speedometers except for their lack of odometer components. The PDF will walk you through how to clean and recondition your gauge.

I won't argue on LBC units. But, on old, old US marques, a drop of machine oil (NOT 3-in-one) on the spindle in the spinning magnet makes a speedo last, oh, 50 or more years between rebuilds.
Depending on how much you drive, no oil, as little as 10 years and it's "kicking", with spindle out of line and magnet catching bowl.
All of mine are oiled, the Jag is when I took the speedo apart anyway.

 

[dklawson]

I am glad that has worked for you. I was taught to not oil the bearings as the oil can thicken and it can attract dust and dirt. Again, I'm glad this has worked for you but it is something I do not do.