Don't think I have ever seen a 240D with a tach, but the 300SD did use the balancer triggered crank sensor for the tach signal through 1984. The 1985 unit (still a 617.95x motor) used a crank senor off the flywheel located in the bellhousing. Engine speed at this time became a signal used in A/C and emission control and sensors similar to the developing gas technology were used.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

The knowledge on this forum is amazing. When under the car replacing the clutch I will see if i cannot get it re-attached just to see if the tach works again, I doubt it will but might be worth a shot.

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Currently
1991 Mazda Miata 174000
1991 Subaru 189,000 Winter beater

got rid of:
1984 VW Vanagon 195,000
1976 350SE Euro 185,000 KM
1973 280SE 4.5 (boy do I regret that)
1980 280SE European W126 4 speed manual (miss it)
1989 BMW 735iL 119000 (good riddance)

I have a 1985 190D 2.2 Auto with the TDC bracket in the glovebox. Do I need this sensor? My tachometer works. Is this thing just for diagnosis? Is it required for IP timing?
Let me know!