How I Fixed My 1984 Vanagon Odometer

After months of thinking that my odometer didn’t work because of a broken or worn-out gear, I finally decided to see if I could learn which gear was bad and look into getting a replacement. What I found was that no gears were worn out. One gear was slipping on its shaft and was easily tweaked to stop the slippage. Now all is fine. Before you go on to my fix, first read a couple disclaimers:

This worked for my odometer. Depending on what’s wrong with it, it may not work for yours. Your mileage may vary. Try this at your own risk. If you break something, that’s your responsibility.
This is not intended to show you how to roll back the mileage on your odometer. That is against the law. It will be easy for someone to see that your odometer has been tampered with after doing this fix, if someone has the gumption to remove it from the instrument cluster and look. For me, since I will never sell my van, this is not a concern. I simply want an easy way to tell when to change the oil, etc.
Your state department of motor vehicles probably requires that you report a malfunctioning odometer.

Getting to the odometer

Remove the instrument cluster

Pull the cover off by reaching to the back of the cover, feel for two indentations for your left and right hands then carefully pull up and toward you. There are several little fingers on the lower front of the cover that are easily broken. Carefully pull until they come out and set the cover aside.
Note the brake fluid reservoir. How weird is that?
Pull the speedometer cable from the back of the speedometer by squeezing the tabs and pulling.
Four Phillips head screws hold the cluster to the dash. Carefully remove those screws. They break easily. You might need to remove some of the headlight/defroster switches to get to the front two screws.
Remove the switches from the cluster. Each switch assembly has two tabs, either on the top and bottom or on the sides, which must be squeezed together.
Remove the connector to the blue plastic circuit board from the bottom of the cluster.

Remove the speedometer/odometer from the cluster

Four screws hold the speedometer to the cluster on the corners. Remove them carefully.
Set the rest of the cluster aside and bring the speedometer to a clean work space.

Remove the cover of the speedometer by removing the two screws on the back.

What’s Inside the Odometer?

From the top this is what you’ll see:

There are two shafts. One holds the Number Gears and is driven by a white worm-gear from the speedometer part. The worm gear is the long white cylinder on the lower right. It’s driven by the reddish gear at the bottom and drives the shaft for the Number Gears. The other shaft holds the Small Plastic Gears that mesh with the Number Gears. Here’s a diagram:

The Small Plastic Gears are loose on their shaft. They can spin whether or not the shaft is spinning. The same is true of the Number Gears. The Metal Gear and the Worm-driven Gear are fixed to their shaft so that when one turns the other does too.

Here’s how it works:

· The worm gear is driven by the red gear from the speedometer.

· The worm gear turns the Worm-driven Gear

· The Worm-driven Gear turns the shaft (red in the diagram)

· The Shaft turns the Metal Gear

· The Metal gear is keyed so that, once per complete revolution, it turns the first Small Plastic Gear

· The Small Plastic Gear turns the first Number Gear one notch (1/10^th revolution)

· When the first Number Gear makes it all the way around (after ten revolutions of the metal gear), it turns the second Small Plastic Gear, which turns the second Number Gear one notch.

· And so on.

What was wrong with my odometer?

Here’s a diagram of what was wrong with my odometer:

The whole shaft (red) had slipped to the right so that the Worm-driven Gear was no longer being driven by the worm gear. My first attempt at fixing it was to simply push the shaft back to the left. This actually worked for 9.9 miles then it got stuck again. The shaft had slipped back out to the right.

This time I roughed up the left end of the shaft and put a dab of JB Weld on it to keep it from slipping back to the right. This time it worked for 69.9 miles. I could see that the shaft slipped as far as it could, but the Worm-driven Gear was still meshing with the worm gear, so something else was wrong.

So I oiled everything in there with 3-in-1 oil (like for sewing machines), pushed the shaft back over just for good measure, and tried it again. This time it didn’t work at all. More investigation became necessary.

How I fixed it.

First I took everything apart to see how it worked. I removed the shaft for the Small Plastic Gears (the blue shaft in the diagram). It is pinched on each end so it won’t come out of the housing. I used Vice-Grips to “un-pinch” one end enough so that I could pull it out. The Small Plastic Gears will go flying if you’re not careful with this. They are all the same, so at least you don’t have to worry about keeping them in order. Make sure you get the end of the shaft rounded enough so that it pulls out with ease. If you try to force it, who knows what’ll happen.

Once the first shaft was out, I could easily pull out the shaft for the Number Gears (well, I had to remove the blob of JB Weld first). All the Number Gears are the same. If one of yours is worn and that’s the problem with your odometer, you can always move it to the last position so it will only try to turn every 100,000 miles. Same goes for the Small Plastic Gears.

I could then see how everything fit together and realized that the metal gear really shouldn’t be spinning on the shaft. I laid the gear flat on a hard clean surface (my kitchen table), placed the tip of a Phillips head screwdriver in the center of it, and gave it a good solid whack to make four little indentions in the hub of it. It did this to both sides. Now the gear won’t spin on the shaft anymore! It’s not too snug to get back on the shaft, but once it’s been pressed into place, I’m pretty sure it won’t spin.

Putting things back together is a bit of a trick. First put the Number Gears on their shaft, one at a time as you push the shaft into the housing. The last one to go on is the Metal Gear. Make sure it goes on the correct way. The little teeth on it have the same configuration as those on the Number Gears. If you look at the picture above, the gears all have teeth all the way around on the left side, but only two teeth on the right side (when looking at them upside down, as in the picture). You’ll have to tap the shaft into the Metal Gear and the rest of the way into the housing.

The next part is the hardest part. Start the shaft for the Small Plastic Gears into the housing; then one by one put the Small Plastic Gears onto the shaft, meshing them with the Number Gears, and making sure the correct numbers stay lined up in the window on the front of the odometer. Note the orientation of the Small Plastic Gears. The skinny end goes to the right (as in the picture). This takes a while, but eventually you’ll get it. Once the shaft is all the way in, double-check the numbers in the window on the front of the odometer. They should be centered in the window. If they are half-in, half-out, you’ll need to adjust them. Once all is well, re-crimp the end of the shaft and you’re done.

I tested mine throughout my experimentation by putting a square bit in my cordless drill and using it to drive the speedometer. At top speed I got about 80mph right there on my kitchen table. It doesn’t take long to go a whole mile at that rate. I can’t remember the size for the square bit, but I know it wasn’t the smallest one.