Repairing the odometer on W123

My odometer started playing pranks more and more often and finally got out of order. In the first time I managed to make it work by resetting the daily mileage. So I decided to repair the whole system.

First of all, after disassembling the dashboard I decided not to remove the arrow – it was fixed pretty tight. This will be useful for those who won’t be able to remove the arrow as well. That’s why there is that small pin everywhere on the photos, although I could have removed it.

First of all you need to make sure that the gearwheels inside of the odometer are able to spin. To do it you should unscrew the two screw-bolts that hold the drive mechanism (photo 7).

And detach the parts (photo 8).

Now the plastic gearwheels do not block the odometer from rotating anymore and it can be checked. Spin the yellow gearwheel forth to ensure that the mileage indicator increases its value. After that reset the daily mileage to zero and twist the gearwheel back – “9999” should be displayed in such situation. If much effort is needed to reach this value, or if nothing changes at all, then the problem is in the silumin gear that can’t rotate properly.

Before starting the repair you will have to remove the brass bushing that is located on the gearwheels axis. It is fixed tight so to remove it you will need to use small pliers and take off the bushing by twisting it left and right. Take it easy as the plastic gearwheels stopper the axis rotation (photo 4).

Here is how the odometer operates.

The yellow brass gearwheel is fixed on the axis. Inside of the body there is a silumin drive gearwheel. It can rotate on the axis but much effort is needed for that. All other gearwheels with numbers can rotate around freely.

After receiving the drive torque from plastic gearwheels the yellow gearwheel rotates together with the silumin one. The change of values is the result of the cooperation of gearwheels with numbers and the locking gearwheels.

These are small gearwheels that have full and half gear-teeth. Each time a gearwheel with number makes a full twist around, a number on the gearwheel to the left if increased by one. This is done by the locking gearwheels. This won’t happen until the number on the gearwheel reaches 9.

In my case the silumin gearwheel started sliding and the odometer refused to function properly. The thing is that the gearwheel receives the maximum resistance during rotation when the number change from 9 to 0 takes place. If this happens on several gearwheels at once then the first gearwheel has to cope with the resistance that is increased due to the bad lubricant in other parts, so it starts rotating on the axis without spinning other gearwheels, and the odometer does not count the mileage anymore.

Do disassemble the odometer you need to whittle down the external end of the axis first (photos 3 and 1).

The flattened part should be whittled down enough for you to be able to push it out of the body with effort. This is pretty important – after you are done you can be sure that you will be able to disassemble this entire part once again later on.

For example, the cable has broken and you need to correct the odometer values so that they display the actual mileage. Or if you want to change the mileage displayed for any other reason. That is what I have done after purchasing my car (I bought a used one) – I have set the odometer values to zero and now it displays my actual mileage from the day I have bought the car, not the total one. We don’t trust those numbers anyway but it’s more convenient for me this way.

Remove the axis and take off the gearwheels. Place them aside.

The next step will be removing the counting unit. When pushing the axis through you can feel the silumin gearwheel resistance. Take off the gearwheels with numbers. They are identical to each other. When pulling down the silumin gearwheel you can feel great resistance in the other parts of the axis. On the place where it was originally located the resistance is lower due to the wear-out of the axis. After removing the silumin gearwheel you can see that there is a ward in its body around the axis. It should be squeezed a little bit to ensure the gearwheel can be put on the axis with greater effort.

Now let’s start assembling it all together.
Before putting the silumin gearwheel on the axis you need to deoil the latter as well as he hole in the gearwheel. This will increase the friction to the maximum. Put on the gearwheel as well as the plastic ones – one by one. Don’t loose the small gearwheel that connects the daily mileage odometer (photo 10).

The next step is: putting on the locking gearwheels. After setting the mileage wanted insert the lockers. To prevent numbers from spinning while assembling the device you can fix them with a piece of a sticky tape. Help yourself with a small screwdriver when putting on the small gearwheels. The gear teeth and the grooves should be placed strictly in a row the way it is shown on the photos 5 and 6.

Push the axis into the body and check the mileage. The position of each number should be in a direct line with each other. If they are not, push out the axis and adjust the corresponding gearwheels with numbers. Make sure the odometer functions properly by spinning the yellow gearwheel. If everything is ok, grease the whole mechanism with an aerosol lubricant and wipe the numbers after done.

Grease the drive mechanism as well (photo 9).

Proceed by inserting any ferrule that is fixed on the small electric motor instead of the cable. Twist it a little bit and get rid of the streaks. Assemble the speedometer and connect the electric motor. Check whether both the speedometer and the odometer are functioning properly.

I would recommend you to reset the daily mileage for several times and repeat the test.

If you have removed the arrow while disassembling the device, you should put it on the way it is shown on the photo 11.

You need to pull the arrow counterclockwise and it should return to the original position by itself. After that carefully throw the end over the block stop. Don’t fix it too tight on the axis – make sure it is installed properly first.

Here are a couple of more views of the daily mileage odometer (photos 2 and 12).

Provided by Vladimir Schegolev aka kit123

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2 Responses

  1. Great write-up! I’ll have to do this soon to my own speedo.

  1. October 29, 2016

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