Hello. My name is Robin. Recently my boyfriend gave me his 300D Diesel Mercedes. I used the car to make a trip to Bakersfield for some personal errands. On the way back, I noticed that the trip odometer was showing some possibly inaccurate mileage reading. By the time I realized that it had broken, I was just about home. Later that day, my boyfriend and I had to run a few errands around town, when he realized that the main odometer had also broken. The speedometer still works properly.

I am hoping that this is something that I can fix. Also, I am fairly new to doing maintenance on vehicles, but I am doing my best to learn how to maintain this car. I hope to gain any feedback from this posting. Thank you all for your time!

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85 300D Turbo Diesel, Sedan. Federal Emissions. 283K.

Here is what you need

http://www.dieselgiant.com/repairyourodometer.htm

Welcome to the forum,

Read that link and you can decide if you want to tackle the job yourself. The odometers in these all seem to fail sooner or later. Fixing them is not that hard, but it's detailed work. Plan of spending an hour or two. If you find the gears are broken, there are some sources to buy replacement gears.

Well, there are some posts that describe how to buy little plastic gears and install them.
I recommend you learn how to remove the instrument cluster. its simple.
Remove the under dash panel, hopefully without cracking it then there is a oil line that requires a 10mm wrench (a short wrench is better than a long one) its on the back side of the oil gauge. Loosen the nut holding it on, blind of course, using your feel (its easy, trust me!) then loosen the nut all the way till it comes out. Place an open plastic bag over the open line and tape it on to catch any small oil drops that might come off it.
Do not start the engine while it's off!
Now push the instrument cluster from the back until it comes out. Don't try to pry it from the front, that's a recipe for broken plastic!
Unscrew the speedometer drive cable.
Now it should come out far enough to see and remove all the wires, noting where they go, the individual wires to the lamps I mean, then the big electrical connector. The wirtes have to goi back to the same spot if you want the right indicators to light when its all back together.

Now carry the while thing over to Palo Alto Speedometer. Let them remove the speedometer and oil it and check for broken gears etc.
If you want to splurge, ask them to replace the trip odometer wheels with a new set and then they will be nice and bright and easy to see!

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'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!

Thank you all for replying to my message. I did notice today that both the main and the trip odometer are trying to roll over again. I'm not fully sure what to make of this, though I am starting to think that whatever is powering both of these, is slowly going out.

I read the web site that I was given a link for. The web site was very interesting, and it looks like something I can handle. I'm curious if anyone might know how much these parts could cost to replace? Thanks again!

They do that. For a while mine would only slip if it got very hot. These guys sell replacement plastic gears for $25 each:

http://www.odometergears.com/subpages/cable.html

If it's just slipping, the gears may be OK. Sometimes the the main drive gear for the odometer slips on the shaft. If can be fixed with a drop of glue (very carefully) or by making the shaft rougher and forcing the gear back into place. It makes more sense when you are looking at it apart.

I just fixed mine last week. Car had 297000 and the odo's stopped clocking miles.

Using the DieselGiant guide I got it apart and easily detemined that the grey colored potmetal gear that is first on the shaft was the culprit.

But I have a few notes that someone might want to consider:

1. The idea is to get the grey gear to bind onto the shaft.
DieselGiant says to use loctite down on the shaft.
I roughed the shaft with a file, but also put some JB weld into
gear hole and then reamed it out to create a press fit on the shaft.
2. To get the gear out I used a drill bit to hold all the number gears,
following in as I removed the long metal shaft so they did not all fall out.
Hope that makes sense.
3. I did have to remove one end of the shaft that had the small toothed
gears that click over the next higher wheel. (To create room to get out the grey wheel).

Small jewelers screwdriver set helped (got it at the dollar store).
Patience, patience. I did the job over two days.
Slip joint pliers helped as I pressed each shaft out and back in.

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80 300D 340K Owned 30 yrs
83 300SD 440K Owned 9 yrs - Daily Driver 150mi/day
02 Z71 Suburban 117,000
15 Toyota Prius 2600 miles
00 Harley Sportster 24k
09 Yamaha R6
03 Ninja 250