Speedometer problem

[Bonnewagon]

I have a nice 1978 only silver speedometer that I scored cheap. Now I found that it may be defective. If I insert a speedo cable and spin it with my fingers, the needle pegs. Other speedos I tested I can use a drill to spin the cable and the needle gets to a speed, then hovers there, like normal. This one seems to be unable to disengage at any speed. How do these things work? Is there some sort of viscous coupling inside? Can it get thick and stick? Is it purely mechanical? Is there a fix for this? I think the odometer is stuck too. The speedo on my Bonnewagon I was able to get inside and re-set it all to 00000. This one I can't move any of the dials. Can that cause the needle problem? I am sure the MPH and ODO are connected so maybe that issue is causing the other? I am stumped by this.

 

[Bonnewagon]

I consulted my enginerd cousin. He says cable driven speedos are made with a magnetic coupling. The cable spins one part, and the needle is connected to the other part. There is no physical connection between them. So as the cable part spins, and magnets spin the needle part. I started to take this one apart and right away I found that the odometer is jammed. I need to be careful as this is very delicate stuff.

 

[SS_Malibu]

Good Luck Sir. Let us know the outcome.

 

[Bonnewagon]

Well, he was right. There is a cup inside attached to the speedo cable . There is another cup that is attached to the needle. Spinning the cable spins the cup, and you can see the other cup follow along, magnetically. There is also a clockworks for the odometer that is driven by the shaft under the cup. Oddly, the magnetic cups were fine, it was the worm gear for the odometer that was jammed. Along the bottom of the odometer dials, there are anchors sticking out that engage a rim to keep them from turning. As the dials rotate, the number 9 spot turns the next dial one number. To make it easy to assemble, the factory added a punched paper strip that holds the anchors steady while you assemble the dials. [Yes, you NEED that!] The paper had broken off, and piece of it found it's way to the worm gear, jamming it up. Once I cleaned that out, all was well. While I was at it, I removed the dials to re-set the odometer to what my Bonnewagon was supposed to be. [ One year at inspection time the odometer reading was input wrong. Now every year the State says my mileage is less than it was the year before and flags me. We keep adding mileage just to get it to pass. Time to fix that] I removed the dial assembly, and changed the numbers to make NY State happy. I had to punch out a strip of paper to hold the anchors in place while I inserted the assembly back into the speedo. NOT easy to do, even with the paper. Now I can put the whole thing into the Bonnewagon. With my current one, the trip odometer is not working. This one works and is a bit shinier too, so I will use it. Being a one-year-only item, these are pretty hard to find. This was not too bad a job. Just be patient, and don't force anything. The yellow paper is what got tangled up, the white paper is what I made. The cup under the number dial will spin effortlessly if all is well.

 

[pagrunt]

To make it easy to assemble, the factory added a punched paper strip that holds the anchors steady while you assemble the dials. [Yes, you NEED that!]

Decades ago when I had my '79 Monte I replaced the original speedo with an extra '80-'85 one. When I was swapping out the odometer drums, both had that paper retainer break. So an extra laminated infantry field data card was used to make a new one. It was way stronger. Wish I still had a few of them for that purpose.

 

[Bonnewagon]

I thought about using something more substantial too. But then I realized that the slotted anchors on the dials engaged that low steel ridge. Once in place, the retainer is redundant. You just need something to hold the anchors in place while you fidget with getting the dial drum into place. If anyone is contemplating doing this, you should know that the numbers that will appear in the speedo window, are 180° from the anchors. When setting the numbers be sure they are directly opposite the anchors, or the wrong numbers will be in the window.