Speedo question

No, not the swim trunks! The speedometer...

Ok, I've got what I think is a mid/late 60's CJ speedo. The trouble I'm having is that the needle keeps bouncing around pretty violently. I've taken the cable and really cleaned it out with brake cleaner, same with the housing. I "lubed" it with dry lube. It turns free by hand, and did improve the bounce some, but not completely. My question is this...do the cables wear out? What I mean is do they develop a rotational "spring" to them?
Also, the speeo mechanism appears to be a magnetic deal, it doesn't appear to be something that could wear out, but I'll ask, can the speedometer itself wear out, magnets get weak, etc?

You help is appreciated!

 

I replaced the speedo with a NOS head after the needle snapped in the bushing going through the face, I also replaced the cable due to running to close to the V8 exhaust pipe. With both of these items new I still get a bounce below 20mph. A couple of mechinacs told me the tcase gear might be the problem. I haven't taken it apart to find out yet though.

 

I've had similar results. Never had a problem until one day I the speedo cable got toasted next to the exhaust pipe. Replaced the cable, but have always had that "bounce" before 50mph since. So I doubt it's the speedo or the trans case.

 

Question. All of your speedo's go up to 90mph, or a different speed? I haven't taken mine above 45, but it has a fair bit of "bounce" to it at all. From what you all are saying, it's not really a big concern, right?

 

I wonder if that mechanism can get clogged with grease/oil/dirt that got gunky. It's supposed to spin pretty freely, and indeed mine did appear to do so, but I imagine any oily type lube may have the potential to foul that up. I didn't do any cleaning to that part of the speedo while I had it out, and I'm not particularly inclined to remove it from the dash after just getting it together. Maybe one of you brave souls can take yours out and clean the magnetic doohicky out with brake cleaner and see if that solves it? Let us know how it works out!

 

As I recall, speedometers use an induction motor to turn the needle. The cable spins an aluminum cup. Inside the cup is a pair (?) of magnets that are connected to the indicator needle and are spring loaded by what looks like a watch spring. The magnets and needle rotate on an axle on precise cup bearings. The magnets create eddy currents in the cup which drags the magnets (and needle) along, at a force proportional to the speed of the cup. I think the main problem would be the spring breaking or dirt clogging up the space between the cup and magnets.

If you can get the thing apart without destroying it, cleaning would have to help. Not many moving parts...

 

You might try cleaning out the cable sheath too.

I've used Slipicone to lube the cables; others have used plain grease.

 

Actually, an update. Cleaning the cable and housing with brake cleaner and then dry lubing it worked fine. I guess it needed a few miles for all the dry lube to work in. Drove it about 50 miles today, and the bounce is 99% gone!