Odometer Repair

Odometer Repair

Here's directions I once copied from the archive. But shoot, why not just send the thing to Rick Borth at Overseas Speedo? He won't soak you, and what he sends back will work perfectly. A Possible odometer fix. (For older mechanical, i.e. not electronic, speedos made by VDO) Symptom: No odometer movement or erratic operation. Read this entire document before proceeding. I claim no responsibility for the validity of this advice. Resetting of a odometers mileage is illegal. Blah blah blah

Remove the speedometer.

Remove the back plate. Notice that there are two sets of number wheels, the trip odometer and the main. Notice that at one end of the main there is a grey aluminum gear/cog.

Push on this cog. Does it spin easily? If so this is you problem and you may read on. If not you must look elsewhere.

This cog is press fit to the shaft and should turn with the shaft. First the shaft, and the gear on its end, must be removed. The number wheels and the cog must be supported while the shaft is being removed. THIS IS IMPORTANT! If the assembly is not carefully supported you will lose you mileage and it will be difficult to reset it.

Find a rod the same diameter as the shaft. Maybe a coat hanger section? I used a piece of welding rod. Begin by prying (gently) the rod out at the gear end. AT THE SAME TIME feed the section of rod into the other end. As the original shaft is pushed out it is being replaced by your replacement rod. Maintain constant pressure ?inwards' by the replacement rod or all is lost.

Hopefully at this point you have the geared rod removed and the temporary rod holding the number wheel/cog assembly in place. Locate the part on the rod where the aluminum cog rides. Sometimes there is a polished band where it has been slipping. (For years?) This section of the rod (~1-2 mm) needs to be ?roughed up' in order for the cog to turn with the shaft. I used a pair of locking vise-grips to knurl the shaft. Be careful! It only needs a little. Too much and reinstallation will be difficult.

Replacement is the opposite of removal. The temporary rod is pushed out by the original. Watch the numbers as you reinstall to make sure they are correct and also not stuck half way in-between a digit. (My ones place is like this but heck if I am taking it apart again!) When the knurled section gets to the cog it will take some force to get it to slid through. A small hammer helps. (Egads!) Or if used wisely, large channel locks. I have done this fix many times with great success. For the sake of redundancy, here's another:

[This was copied from a procedure for Porsche speedo's; is said to work for MB's as well though. (JK, 7/18/00)]

Separate the face and the "guts" of the speedometer from the housing--they should fall right into your hand. The numbered rollers and some gears are housed inside a U-shaped piece of metal. When the car is rolling, the drive cable turns. This torque goes through some reduction gears, and turns a gear on the outside of this U. The gear turns the shaft it rides on, which goes through one set of rollers to turn a silvery pot-metal gear that is on the same shaft. This gear is what causes the rollers to turn. The problem typically is that the pot-metal gear is now loose on the shaft, and does not turn when the shaft turns. Verify that this is the case for your unit. You can use the reset cable to turn the speedometer input. It will take quite a few turns to see any movement out of the odometer. Use the tape to tape the rollers in position. Pull the outer gear and shaft out of the U. Make a note of where the pot-metal gear rides on the shaft. Be sure not to let the rollers get loose! Next, use the pliers or the punch to knurl the shaft at the place where the pot-metal gear rides on it. Dirk Bergstrom tells me he used a scribe to put grooves along the length of the shaft at that spot. The object is to make the shaft rough enough that the gear will not spin on it. Now put the shaft back into the U, through the rollers, and through the pot-metal gear. Optional: Put some glue or epoxy on the gear-to-shaft joint. Be careful not the glue the shaft to the U or the rollers! If you've really got the shaft roughened up, it may take some real pushing to get it back in all the way. Test the works using the reset cable. Again, it will take lots of turns to move the odometer a small fraction. Next, put the guts of the speedo back in the "can". Screw in the two slot-head screws that hold the guts in. Place the glass bezel and trim ring(s) back over the end of the can, and carefully bend the edge of the ring over the lip on the can. You do not have to be *too* careful, since this rear part of the trim ring will be sitting flush against the dashboard face. Now you can put the speedometer back into the car, hook it up, and test it for real!