Hey everyone,
My green 300SD's odometer failed yesterday so I decided to investigate. From what I've learned here the drive gear and one of the other gears fail. Sure enough, this was the case for my 300SD as well. What I didnt see on here was too many pictures so I decided I'd take some and post up..
Step 1) Remove Instrument Cluster from Car.
Step 2) Remove Speedometer section from cluster.
Step 3) Remove plastic backing plate via small screws.
Step 4) Inspect your gear train for damage.
As you can see in my second photo my drive gear is missing several teeth as well as the gear that it meshes with.
Step 5) Source replacement gears. You can either buy them for ~$65 from
Odometer Gears - WELCOME or if you have a spare speedometer see if the gears are compatible. Luckily I happened to have a spare 560SEL cluster with the same tooth count gears so I simply swapped them over.
Installed replacement drive gear:
Finally:
Step 6) Replacing Capacitors.
Since you have the speedometer out, you might as well replace the capacitors. For my 300SD, there were three. The replacement were easily obtained from Radioshack for about $4.50 or so.
To gain access to the capacitors you must desolder the speedo from the circuit board. There are a few connections to desolder, these are indicated below in the picture:
After that you are free to replace the capacitors, the values are as follows: 2 x 220uF @ 6 V, 1 x 47uF @ 16V. RadioShack carried ones that were rated at 35V so we were set.
Here are my replacements installed:
Step 7) Reassembly
After you've finished soldering, just re-assembled everything back as it was. Be sure to re-solder the contacts for the speedo unit to the circuit board and you're all set.