Do I need a new speedo...

or can this be fixed?

My speedometer core is turning coming off the xfer case, by the needle does not move. The odometer works and I can bounce the needle by manually turning the back of the speedo.

Not sure how these things work :?, but is it fixable or should I replace it? It only has 5,000 miles on it since it was installed.

 

The odometer is just a gearbox connected to the number wheels. If the cable turns, the odometer should advance.

The speedometer is an induction motor, typically an aluminum cup connected to the indicator needle. There's a spring, like a watch spring, that keeps the needle at zero. Inside the aluminum cup is a magnet that turns inside the cup when the cable turns. The magnet induces currents in the cup ("eddy currents") that oppose the changing magnetic field. This creates an electromagnetic force that turns the cup against the spring. The faster the magnet spins, the more force, and the further the cup turns against the spring.

These things turn on jeweled bearings, just like a watch. Typically they either wear out, or get gunked up with decades of dust and dirt. I'd take the speedo head out and connect it to the cable, and see if the magnet turns when the cable turns.

 

Three places for things to go wrong.
#1 Bad speedo cable. Disconnect from the back of the speedo (unscrews) drive jeep, observe cable end. Is it spinning counterclockwise? Yes? Good sign. Cable is probably ok.
#2 Speedo gear in the transfer case, they get worn out. I don't know about the D18, but they're made of unobtanium for D20.
#3 bad speedo. The speed indicator needle is not directly connected to the cable, works on magnets as far as I can tell. Pretty delicate deal. However there is a tiny hole just above where the cable screws into the speedo, that you can apply a drop (one drop) of oil to. I think this is to lube the gears for the odo.
Does your odo work? My odo works fine, but my speedo needle gets goofy above about 45mph, works fine below that speed. When I first put the cable in, it was goofy at all speeds. Somewhere I read that there are two different length cables, and if the one you get is two long, the speedo will be jumpy. I cut about 1/4" off the end of the cable that fits in the transfer case, and that seemed to improve things a bit. I'm gonna cut a little more off, and see if i can get the thing to work in a reasonable manner over 45 mph.
If you speedo is new, I would tend to rule out a bad speedo, but then again, some of the aftermarket parts are of inferior quality compared to the originals, so anything is possible. But at $100, I would explore all other roads first.
Don't feel bad, I've been fighting this for 6 months.

 

I'm sure glad Billy didn't start this thread... R) R) R)

 

Thanks much - that is exactly what I needed to know. Guess I'll pull the head and do a little more trouble shooting. I just hate pulling the dash to get to it - PITA.

 

Hmmmm. Well, I pulled the speedo head today. Put it on the bench and tested it. When the cable is connected tightly to the back of the head unit the odometer will turn but the speed needle is locked down. If I loosen the cable connection, the speedo needle will turn.

In the jeep with a loose connection, the speed needle works, but it will climb all the way to 90 mph and stop there.

I think the cable connector is touching the brass colored receiver where the cable core inserts on the head unit. This is keeping it from turning freely. Problem is, I don't see how to correct it. Any thoughts?

 

anyone figure this out? My Odometer is working but the speedometer needle doesnt move...

 

I saw the same behavior in the speedo on the '70, and I cut down the length of the core by about 1/4 or a little more. This seems to have cured it.
I think the repro cables available from the vendors are a little long. I got mine from Walcks I think.

Don

 

Tim I have removed my stewert warner speedometer from the dash and took the outer housing off and found a small shaft extending out from a round disk flopping around. One end is not connected to anything. Should it be connect to the watch like spring you mentioned above? Is this what turns the needle? The shaft appears to be larger then the hole I see where it could possilbly have once been connected. May be the small shaft was turned down smaller yet at the very tip??

IF this is broke is it repairable or time for a different speedo?

 

Here's my Stewart Warner Speedometer out of my 1970 cj5, odometer works but speed needle does not move. Number along front face perimeter is 827509 Numbers on the back are 543NXU9 and below this number is another which is SF6457206. The 7 may be a V its really rubbed out.



This is the back of the speedometer as removed from my cj5 jeep. All lights and wiring removed by PO. I would like to see a photo of the back of speedo with wiring and lights in place if someone has one to share.



Is the shaft at the end of the pen supposed to connected to the jewel bearing/watch spring thingy? My guess is yes and this is why the needle does not move.



Is it time for a replacement or can this be repaired. Also what part number for the light sockets.

 

Brem10mm, that speedo on ebay I sent you info on just sold for $36.00 and had the light sockets with it. It was for an 83 but if the gauges didn't match your senders you could put your gauges in it. Did you get this one on ebay?

 

Yes, thanks Walt

 

Anytime.

 

The needle is supposed to be attached to the shaft connected to the aluminum cup. The needle, axle, and cup all should turn freely against the resistance of the watch spring. The speedometer cable spins a pair of magnets inside the cup that create opposing currents in the cup (eddy currents) and form an electromagnetic coupling between the spinning magnets and the cup. The faster the magnets turn, the larger the eddy currents get and the more torque on the cup. The watch spring is calibrated to resist the rotation of the cup; if the spring is damaged or the axle is out of it's bearings, then you will have a hard time making the speedometer work accurately again.

Sometimes all these speedos need is cleaning to work properly again. But, they are rather delicate, and if they've been tinkered with roughly they can be damaged beyond easy repair.

A speedometer shop could probably fix it, if all the parts are there. But I think that's going to be uneconomical. Aftermarket replacements are available, and used ones come up for sale, as Walt pointed out.

 

Speedometer repair shop in Denver. I haven't used their services yet, but I will be. I have several 1956 speedos, I need them to make me ONE good one from them. Two would be better. http://www.deluxespeedometer.com/