My speedo does not come up to speed with the car and when it does come around to pointing out that I am no longer sitting at a light it seems to be reading slow i.e. the speed in MPH matches what is displayed in the KPH reading.
This is just a coincidence I'm sure but is this a cable issue or a speedo issue? Is the cable hard to replace?

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'99 S420 - Mommies
'72 280SE 4.5 - looking to breathe life into it
'84 300SD Grey - Sold
'85 300SD Silver - Sold
'78 Ski Nautique

Speedo problems are very difficult to diagnose. Everything from tire size to the drive gear in the tranny can impact operation. However, if I were you I would replace the cable first as it is significantly cheaper than rebuilding the speedo. And when I did, I'd have a look at the drive gear to make sure it's OK. It isn't hard to do, but you are working in a confined space and it will take some time. If you search here you'll find the exact procedure outlined. If that doesn't solve your problem, you'll have to have your speedo rebuilt. Someone here does them, again, a search will tell who. Good luck.

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1982 Mercedes-Benz 300CD
1982 Mercedes-Benz 240D - stick

Thanks for the input.
I kind of figured that I was going to have to do the cable I was just hoping that someone else might have experienced this phenomenon before and give me a definitive answer as to the problem. I hate replacing things without a complete diagnosis.
It seems that it must be connected as i do get a reading it is just very slow in coming up and then does not read teh actual speed but about 15 mph under teh actual speed. I doubt the highway patrol will let me off because of this one so I guess I'm going to havet o bit ethe bullett and fix it.

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'99 S420 - Mommies
'72 280SE 4.5 - looking to breathe life into it
'84 300SD Grey - Sold
'85 300SD Silver - Sold
'78 Ski Nautique

I have heard from a friend, that he sprayed some brake cleaning fluid down the cable from the top end( after removing the end that goes into the meter) This will loosen the gunk and then spraying some graphite lock spray of silicone oil in there.
He fixed it this way and it worked for him 2 years until he junked the car.

Just give it a shot.

MVK

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One penny saved is three penny earned.

1985 300D Turbo 179,000miles