A few months ago, my speedometer needle started jumping around. I ignored it(bad move!)
A month or so later, the needle had stopped moving at all, and the inside of the glass was "dirty" or dusty.
I figured the drive cable had snapped, so I ignored it for another couple of months.
When I finally got around to investigating, I found the drive cable was fine. "Luckily" for me, someone had already taken this unit apart, and the bezel was already pried most of the way open, with just a few points re-crimped. So it was pretty easy to get the Bezel, Bezel Gasket, Glass Retainer, Glass, Glass Gasket, and in my case, the piece of the dial that stays with the bezel(the outer ring) off. I found once I got inside, that some of the "guts" were loose. Further investigation showed that the Field Plate had come loose from the Main Frame(the 3 screws were rattling around in the bottom of the Case).
Here is an illustration, which may help:
Further disassembly showed that the Hair Spring Pin was flopping around in the Rear Jewel Bracket. The Rear Jewel Bracket is supposed to contain 2 pieces of a very hard substance; one of them, which is flat, merely sits in the bottom of the hole in the bracket, taking the end thrust from the Hair Spring Pin, while the other one, which was completely gone in my speedometer, has a hole drilled through it, which the Hair Spring Pin passes through. These 2 "jewels" (which look like a ceramic or glass material to me) are the bearings for the rear of the Hair Spring Pin.
My first thought was to contact someone like Perry Ruiter who rebuilds these things, but my finances are not so great these days, and a quality rebuild was probably going to cost me more than I could afford to spend right now. So I started thinking about how to do the job myself, if only to just get the speedometer working again.
I spent quite a lot of time researching jewels for watches and clocks, and found that the type of jewel I needed, which provides both radial and thrust bearing surfaces, is called a "balance jewel", and it is the most delicate(and usually the smallest) jewel in a watch or clock mechanism. I needed one with a 1mm bore, and the largest I could find was about 0.12mm.
I also contacted the aforementioned Perry Ruiter, who was very helpful with advice, but could not tell me where to find a replacement jewel. He did mention that a friend of his had made a repair using a tiny ball-bearing, and he would ask his friend to contact me if I wished. I said, "Yes, Please!", but the friend was obviously not so inclined, so I started to look further into it.
I found a place that sold 1x3x1 ball bearings (that is 1mm bore, 3mm OD, and 1mm thick) at a reasonable price, so I ordered a few of them. When I got them, I was able to press one onto the rear of the Hair Spring Pin, with moderate finger pressure.
The problem I now had was that the hole in the Rear Jewel Bracket was ever-so-slightly larger than 3mm. I used a small drill bit to ream out the crimps in the hole in the Rear Jewel Bracket, and started pondering-If I had a very thin-walled tube, of 3mm ID, I could press it over the OD of the bearing, and then insert the whole assembly into the Bracket. I had no such metal tubing, but then I remembered that, being in the electronics business, I had quite an assortment of plastic insulating and heat-shrink tubing.
I found a piece of heat-shrink that fit snugly over the bearing OD. I cut a 1mm slice of it, put it over the bearing, and assembled the whole thing....and it works!
It remains to be seen how long it will last, but so far, i am pretty happy with my $10.00 repair.
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