I tinkered with idea of trying to match up the ODO to reality. The one I replaced it with has more showing, so it would have to go backwards. I found when you spin the gear backwards (as if you're going in reverse) the ODO it will reduce mileage only up until the "3" displays in the rightmost digit position. It won't go any lower. Something starts free-wheeling at that point, so it seems at most you can only reduce an ODO by maybe 9 miles. I wondered if this was just my sample, or if this was general case?

It kinda makes sense if it is a design feature because most people 1) don't care about ODO reduction while backing up, and 2) don't drive backwards continuously for more than a little bit, and 3) prevents fraudsters from burning out drills to make false readings.

I looked at ways of lifting or accessing gears and tumblers directly, but the unit is all packed in there quite nicely... and many approaches would in fact require removal of the dial and faceplate, and possibly lifting the plastic gear cage up out of the metal housing... and ... given my recent needle breakage and feeling low on spare speedometers, I thought not.

But if you want to post a helpful how-to-rollback-your-odometer DIY page for Mercedes owners, I'd read it and try. So would said fraudsters so maybe not a great idea. PM me instead!

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Cheers!
Scott McPhee

1987 300D