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There has been a bit of talk on resetting a speedometers odometer to zero again or any other mileage setting your looking for. So since I'm resetting one to 00000 for a cx500D that I'm building I thought I might as well take pictures of the steps it takes and post them here for you all to refer to. The speedometer I'm doing is from the custom style with the separate gauges. The same process works for the Std. style as well. But it's a lot more difficult to reassemble the two halves of the Std. style gauges than it is to do the type I'm showing here.
OK, here's the specimen I'm resetting. The chrome band that connects the two halves needs to be cut to get the assembly apart. I've seen people pry up around the back side of the ring to get them off but I prefer this method. It looks much cleaner in the end. I'm using a Foredom with a flex shaft that has a very thin cutting wheel on it to cut the band. But there are other ways to cut the bands.
With the band cut you will need to use a thin knife or scrapper to pry the two halves apart. Be patient and don't force it too hard. These have been pressed together for 30 years plus and need to be coaxed slowly.
After the two halves are apart you need to take out the two screws that hold the main unit into the back half. Sorry I forgot to take that picture. But the screws are next to the drive unit that the cable goes in.
Now you need to remove the screws that hold the face plate on. Be careful not to slip. The face is plastic and you don't want to break it.
Now comes the tricky part. Getting the needle off. They are pressed on pretty tightly usually. If you try to pry it off between the plastic face and the needle you take a chance of marking things up or breaking the needle. What I do is to put a screwdriver UNDER the plastic face plate just under the needle and twist it to pop off the needle. Be careful where you place the screwdriver though. You don't want to pry against any plastic parts like the rollers with the #'s on them.
While I'm writing this I thought that the reset procedure COULD possibly be done without pulling the face plate and needle off. I'll give that a try on the next one.
Now on the side you'll see a copper clip holding a spring and plastic collar in place. Push this off with the edge of a flat screwdriver.
Here is what the clip looks like.
Next you'll see the second clip that holds the numbered rollers together tightly. Take this clip out too.
Now is where you can reset the rollers to the # you choose. Start from the left side by sliding the roller to the left. This disengages the gearing in them and allows you to roll it. Be gentle. They tend to want to catch as you turn them if they are not pushed totally away from the adjoining roller next to it. When you get the one moved to the # you want, slide the next one over and rotate it to what you want. This is done with each roller one at a time from left to right.
When your done with all of them you'll end up with a gap between the tenth # roller. This one is engaged to a metal gear and isn't worth trying to move.
Now you can reverse the clip removal steps and put it all back together. When I'm done I always test the unit with a drill driven in reverse to make sure it all works for a mile or two. Believe it or not you can also reverse that by running the drill forward before you put the needle and face back on.
OK, here's the specimen I'm resetting. The chrome band that connects the two halves needs to be cut to get the assembly apart. I've seen people pry up around the back side of the ring to get them off but I prefer this method. It looks much cleaner in the end. I'm using a Foredom with a flex shaft that has a very thin cutting wheel on it to cut the band. But there are other ways to cut the bands.

With the band cut you will need to use a thin knife or scrapper to pry the two halves apart. Be patient and don't force it too hard. These have been pressed together for 30 years plus and need to be coaxed slowly.

After the two halves are apart you need to take out the two screws that hold the main unit into the back half. Sorry I forgot to take that picture. But the screws are next to the drive unit that the cable goes in.

Now you need to remove the screws that hold the face plate on. Be careful not to slip. The face is plastic and you don't want to break it.

Now comes the tricky part. Getting the needle off. They are pressed on pretty tightly usually. If you try to pry it off between the plastic face and the needle you take a chance of marking things up or breaking the needle. What I do is to put a screwdriver UNDER the plastic face plate just under the needle and twist it to pop off the needle. Be careful where you place the screwdriver though. You don't want to pry against any plastic parts like the rollers with the #'s on them.
While I'm writing this I thought that the reset procedure COULD possibly be done without pulling the face plate and needle off. I'll give that a try on the next one.

Now on the side you'll see a copper clip holding a spring and plastic collar in place. Push this off with the edge of a flat screwdriver.

Here is what the clip looks like.

Next you'll see the second clip that holds the numbered rollers together tightly. Take this clip out too.

Now is where you can reset the rollers to the # you choose. Start from the left side by sliding the roller to the left. This disengages the gearing in them and allows you to roll it. Be gentle. They tend to want to catch as you turn them if they are not pushed totally away from the adjoining roller next to it. When you get the one moved to the # you want, slide the next one over and rotate it to what you want. This is done with each roller one at a time from left to right.

When your done with all of them you'll end up with a gap between the tenth # roller. This one is engaged to a metal gear and isn't worth trying to move.

Now you can reverse the clip removal steps and put it all back together. When I'm done I always test the unit with a drill driven in reverse to make sure it all works for a mile or two. Believe it or not you can also reverse that by running the drill forward before you put the needle and face back on.