Classic/Antique Car Repair: 1965 speedometer, speedometer repair, outer sheath

Question
my new 65 mustang convertible speedo is erratic.  The needle
bounces across the numbers and doesn't maintain steady
tracking.  Is this the symptom of a bad cable or speedo drive
gear?  As always, thanks for the help.

Answer
There are a bunch of possibilities, the cheapest one to fix is a kinked or dry cable, so try that first. Get some speedo cable lube (it's special stuff with graphite in it) from your local parts store and lube the cable.  To do that, disconnect it from the speedometer head, and pull the center of the cable all the way out.  It is probably filthy, so don't get it on your clothes or the upholstery of the car.

When you have it all the way out, stand up and let it hang from one end - see if it hangs straight, with no bends, and then twist it between your fingers to see if it turns smoothly without whipping around.  If it does, it's OK.  Now put a good bit of the lubricant on it and feed it back into the outer sheath of the cable.  Push it all the way in, turning it as you go - when you get it all the way in it will resist turning.  If you find a place where it resists turning before it is all the way in, your outer sheath has a kink in it, or too sharp a bend.  Find out why - and fix or replace it.  That was probably your problem.

If you can find no problem with the cable, then you need to try lubricating the input bushing on the head.  Feel above the fitting where the cable goes in to see if there is a small hole up there - there probably is.  If so, get some 3-in-1 oil or sewing machine oil, and put one or two drops in that hole (no more!).  Then put it back together to see if the problem is gone.  If not, the head is going to have to come out and be taken to a speedometer repair shop for a rebuild.

Dick