Note that my bezel (black) is already a little rough. This speedometer has been opened once before by me. The bezel has cutouts that match those mounting arms on the sides of the speedometer. Remember to clean the glass/plastic. Use cotton not paper towels.

This series illustrates the steps in fixing an odometer that doesn't work. The speed was registering just fine, but the miles had stopped moving.

The first photo is the process of unbending the front bezel. The bezel is crimped in place, and that is how you get into the speedo. You must unbend it a little bit at a time, and work your way round. I've found that I can usually get the speedo apart with about 1/2 of the front bezel uncrimped. If you work carefully this can be done with very little damage to the bezel. You won't see the back when the speedo is installed.

To crimp the bezel back, reassemble everything, and again carefully work your way around the bezel pushing the crimped part back down.

 

The front bezel and glass are off. The fule gauge is still attached.
Fuel gauge removed. It has 2 screws, and an electrical spade plug to a resistor-thingy. The resistor-thingy is a little black box with a single screw. I'm not sure what the resistor is for. I opened up the box and found a light bulb inside. I'm guessing it compensates for some current flow or temperature issue.
The fuel gauge plugged into the resistor-thingy.

Before removing the speed needle, very gently lift it over the stop. Not it's resting position. It is spring loaded and must be pushed back onto the speedo shaft exactly in this resting location. Otherwise the speed will be off.

I forgot to note the resting position, and now I have to open up my speedo and calibrate it. That will be difficult, and error prone. My plan is to first calibrate the speed with the mile markers along side the highway. (I think it currently reads 70 mph at an actual speed of 45 mph). I'll use a variable speed motor (my drill) to make 70 read 45.

 

Inside you'll probably find that the gear on the end of the odo drive shaft is slipping. In this photo you see the long odometer worm gear, with the small odometer drive gear below.

 

 

An enlargement. In this photo I had tried epoxy on the odometer drive gear. It did not work.
The cup shaped driven part of the speedo. The speed needle is at the other end of the shaft with the silvery cup.

The thick donut shaped thing is a magnet. It drives the cup in the photo above. The faster it spins, the more the magnet drags the cup, the needle moves. I've heard this referred to as an "eddy current motor."

The white shaft is a worm gear that drives the worm shaft that actually turns the odometer numbers.


Here, the odometer drive has a replacement brass gear from a salvaged speedometer. While I had the odometer apart I was going to reset the odometer (since it han't worked for years). It looks like I forgot two digits. This is a tedious step, and I wasn't about to repeat it just because the mileage was 66000 instead of 00000.

If you have to remove the odo central shaft, first the second shaft has to come out. It is crimped at both ends. I just filed off the crimped par on one end, allowing it to slide out.

It is a good idea to study the odometer function before taking it apart. The small gears on the second shaft are tripped by a tab on the numbered wheels. One rotation of the numbered wheel trips the small intermediate gear, and that indexes the next larger number by one digit.

 
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