Hello fellow enthusiasts,

I have a question concerning my 1985 MB 300 SL (euro spec) which apparently decided to stop tracking miles. A local mechanic said that there is a sensor that is located under the car next to the transmission that may be at fault.

Please advise if you have any suggestions and or part number to help me solve the problem.

Thank you.

 

I had same thing with an 83 diesel. Found that it was the nylon gears on side of the speedo housing, which are easy to access and remove with just 2 screws.
Unfortunately I checked today and the replacement gears (3 about size of a quarter and another much smaller one) are very expensive, like $70/set or more.

so unless you can find these cheap, or have a different problem, a wrecker might be the best bet. I got an instrument assembly from a pick-a-part for a 8-cylinder gas (yours I think) that looks the same but the odo is running about 15% too fast. It was running way fast until I pulled a little plug-in component out of the back.

They are mechanical but are run by an electrical signal.
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Thanks, I guess Im going to have to bite the bullet and have the MB dealer give it a look and quote me the job.

 

I imagine it might be a hell of a lot more than $60 or 70 if the dealer does it.
If you don't mind spending that sort of money ($60 or so) the nylon gears I think are the way to go, since it's quite a simple job and you retain the setting of your existing odometer. I just resent having to pay that much for things that are worth about $2.

Btw this was for the 300SD which has the elecitrical speed input (probably like yours), not the 300D style which I think has a mechanical cable coming in to the back of the odo/speedo. If yours has the cable input I think that is usually much easier to fix for free with a bit of super glue.
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Thanks for the input. I unfortunately, dont have the guts to take my dash apart to try and fix this due to my limited experience. Paddo, you say its a simple job? My speedometer is indeed mechanical. Maybe there is a link that can help me gain some courage (diagrams) to take this thing apart and fix this thing?

 

I think I found one for the cable odometer on this forum the other day. Search odometer and you should find it.
Can you get your instrument panel/ speedo/dash assembly (0r whatever it is called) out? That's often the hardest part esp if you haven't doen it before. Should be instructions in this forum somewhere.

If yours in fact does have the mechanical cable input, there should be a sort of worm gear on the side of the unit that looks like it comes off pretty easily. I'm going from memory of seeing the post a couple of days ago and didn't pay much attention coz it is not the type I have.

Anyway it said something about getting some locktite or super glue and using it to lock the worm gear on the shaft (after cleaning with solvent) because it comes loose. Then reassemble and it should be fine. Sounded very simple but best laid plans of mice and amateur mechanics etc. If you can't find the post write back and I'll try to find it.
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Ok here's the link:

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

I hope it isn't the problem that the one in the link has since that looks tricky.
Hopefully it's just the little brass gear that runs off the long nylon worm gear.
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Thanks paddo, I'll look into it and see if I can come up with the courage to do this job myself.

 

Haven't done one of the cable driven ones myself, just mine which is driven by electrical signal. I have read somewhere that the most common problem is the little gear that runs off the worm gear coming loose, which I think is extremely easy to fis just by dabbing a bit of locktite or super glue into where it goes on its shaft. So definitley worht taking it out and having a look I'd say.

In my case I might begrudginly invest the $70 or so for the plastic gears since I imagine every one off a diesel would have the same problem or be about to any minute - and I could then keep my existing odo reading. But yours should be free apart from time and possible scraped knuckles when extracting it from the dash.
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