The Odometer is dead in my 1987 300TD wagon. I have another working one with almost the exact same mileage, but it is from a Gas W124.

I have put this into the diesel and it seems to work, but it is about 20% off. Reading about 48mph when I am actually going about 60mph (using my GPS to check it).

I have not found anything that says exactly what the differences are between the Gas and Diesel speedo setups if there is any. This speedo could be bad.

Are there known differences between Gas and Diesel Speedometers?
I would guess that the only differences would have to do with the cable somehow, because I cant find anything online that shows different parts for the two different types.

I am going to try and rebuild the odometer on the original speedometer and I also have a 1994 gauge cluster from a Diesel sedan that I will try to put in. I think that the later gauge clusters have better light distribution.

Could it be that I can just measure the gears and replace them with ones from here to get the correct ratios:
Odometer Gears - Mercedes-Benz - E class (124) 84-95 Mech.


I guess I just did not really put it together that the gears have subtle size differences and that may account for a Diesel / Gas difference.

Just guessing.

Hopefully someone much smarter than me can be definitive.

the diesel has a 2.65:1 rear diff ratio that the speedo is geared for.
the gasser (300 series, not v8 ) would be a 3.27ish:1 rear ratio, so your speedo would read low speed, and low miles driving in the Diesel...

__________________
John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

Been There Done That

See this spreadsheet for what will work (thanks gsxr)

http://www.w124performance.com/docs/mb/other/differentials.pdf

__________________
The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech

I just replace my in my 87 300TD and I used one from a gasser a 95 E320 same gear ratio works fine

That is correct, there are several gas powered Gen II 124s with that same 2.65 rear end so the speedo will cross over to the Gen I 124 Diesels.

That is what I did to fix my car.

__________________
The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech

I've successfully swapped the instrument cluster in my 1987 300TD with the one from a 1994 E320 gasser. I had to keep the original '87 tachometer and fuel gauge, but speedo was a direct replacement. Tested with my GPS and speed is accurate. I would recommend using the housing from a later model as the illumination is much better.
I also transplanted the '94 instrument needles to the fuel gauge and the tach as mine were faded and yellow. Now all are bright and orange.

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1987 300TD (wagon)

For posterity:

- the F-O-T gauge cluster is identical between 124 gas and Diesel
- As mentioned before the speedometer in certain Gen II gas 124s will cross to a Gen I 124 Diesel
- Tachometers will not cross between gas and Diesel, the Diesel ring gear pickup has 144 pulses/rev and the gas has 3 pulses/rev (from the ignition system). The gas tach will be buried at 7k as soon as the engine starts spinning. BTDT on that one too.
- The housings are interchangeable and as mentioned the Gen II housing has much better illumination.

Extra credit:
- If you get the F-O-T from a gas car with the Economy gauge, it can be converted to a boost gauge, or hook it into your transmission vacuum line.
- The later 5-pin temperatature displays can be adapted to serve in the place of the older 4-pin displays. Be sure to save the 5 pin connector from the donor.

__________________
The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech

I've fixed a couple of the temp displays by upgrading to the 5 pin.