This weekend I swapped my speedometer in my 420sel for one from a 84 500sec. I know that the SEC had 14" wheels and now the speedometer and odometer wll be innacurate. Is there another way to correct this other than getting 14" wheels or new gears in the instrument cluster? I know some cars you can change the gear in the cable at hte transmission. Is this possible on my merc? Thanks.

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1984 300SD Orient Red/ Palomino
1989 560SEC
2016 Mazda 6 6 speed manual
1995 Ford F-150 reg cab 4.9 5speed manual

First of all speedometers are designed for the differential gear ratio. Are both speedometer made for the same ratio? There should be a sticker or stencil onthe back of the gauge that has the ratio look for something that says 2.88 or 3.07 etc. What size tires does the car have? It could be that the outside diameter is the same between say a 14 and 15 inch rim size if the 15 inch is a lower profile tire. If the speedometers are designed for the same gear ratio and the tire diameters are close you should be OK. If the speedometers are for different gear ratios, you can get an adapter that will go on the transmission sender or you can have the speedo rebuilt. There are places that specialize in MB (VDO) units.

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"I have no convictions ... I blow with the wind, and the prevailing wind happens to be from Vichy"

Current
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'74 Jeep CJ5
'97 Jeep ZJ Laredo
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Bruno '81 300SD
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'92 Subaru
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'71 Buick GS conv
'67 GTO conv
'63 Corvair conv
'57 Nomad

Well the gauges came from an 84' 500SEC. It was at Pick-N-Pull with no wheels so I'm assuming it had 14" wheels and I have no Idea what tires it was calibrated for. I'm not totally sure that the odometer and speedometer are off, but I checked the spped and mileage vs a handheld GPS and they are not synched. It's not a big deal, but I would like to get the speedometer correct. I guess I'll pull the cluster back out and see if it matches the original one. The new one had a sticker that said it was repaired and calibrated by some company in Houston,TX. My tires I believe are 205/65R15

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1984 300SD Orient Red/ Palomino
1989 560SEC
2016 Mazda 6 6 speed manual
1995 Ford F-150 reg cab 4.9 5speed manual

It doesn't matter anymore as that odometer quit working this morning.

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1984 300SD Orient Red/ Palomino
1989 560SEC
2016 Mazda 6 6 speed manual
1995 Ford F-150 reg cab 4.9 5speed manual

126 odometer's have a common failure of at least one of three gears. you can buy just the gears from this guy at www.odometergears.com

I bought a set for a 500SEL in the past- they came quick and he even called me to verify, real nice guy.

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1980 500SE/AMG Euro
1981 500SEL Euro
1982 380SEL
1983 300TD
1983 500SEC/AMG Euro
1984 500SEC
1984 300TD Euro
1986 190E 2.3-16
1986 190E 2.3
1987 300D
1997 C36 AMG
2003 C320T 4matic

past: 1969 280SE 4.5 | 1978 240D | 1978 300D | 1981 300SD | 1981 300SD | 1982 300CD | 1983 300CD | 1983 300SD | 1983 380SEC | 1984 300D | 1984 300D | 1984 300TD | 1984 500SEL | 1984 300SD | 1985 300D | 1986 300E | 1986 560SEL | 1986 560SEL/Carat | 1987 560SEC | 1991 300D 2.5 | 2006 R350

Thanks. I will rebuild my unit.

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1984 300SD Orient Red/ Palomino
1989 560SEC
2016 Mazda 6 6 speed manual
1995 Ford F-150 reg cab 4.9 5speed manual

Here's a how-to for the electronic speedometer version
http://www.peachparts.com/shopforum/showthread.php?t=206598
...and for the older, mechanical version
http://dieselgiant.com/repairyourodometer.htm

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1986 560SL
2002 Toyota Camry
1993 Lexus

Cool, I was gonna need to dig up that info as soon as I get my gears, and I suppose I'll do white face gauges at the same time.

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1984 300SD Orient Red/ Palomino
1989 560SEC
2016 Mazda 6 6 speed manual
1995 Ford F-150 reg cab 4.9 5speed manual