I have a challenging question for you. My 1984 300d with 264000 on the clock had the original engine replaced at 250,000 miles with a good used engine from a 1983 300d. On
my 1985 300cd there is a speed sensor on the
flywheel cover to signal the tach. However the 1983 got its tach signal from the diagnostic plug. Do you know of any practical
way for me to restore the operation of my
tachometer? By the way, I thoroughly enjoy the information that is available on this website!!

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kjcalhoun
Bosch certified DFI Tech
20 years experience
MBCA Member, Southern Stars
1984 300D
1985 300CD

On a more serious note, I don't get it.
Am I missing something here ?

On the fender there is a diagnostic plug that processes the signal for the tach. IF it fails, the tach doesn't work. We have them in the PartsShop to the left of this screen.

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Benzmac:
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM

BENZMAC,

I am confused by your reply. According
to the 123 cd-rom, the 1984 and 1985 diesels
don't get the tach signal from the diagnostic plug, but rather from a speed sensor near the flywheel. I have seen the diagnostic plug mounted tach sending unit on pre 1984 diesels
but the 1984 and 1985 diesels just have a plastic cover. Since the replacement engine is from a 1983, it doesn't have the flywheel mounted speed sensor. Do you think that if I were to put a tach sending unit in the diagnostic plug, it would provide the necessary signal to my tach. It is too expensive a part to buy for nothing. Your help in this matter is greatly appreciated as I hate to have gages and indicator lights that do not work.
Many Thanks

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kjcalhoun
Bosch certified DFI Tech
20 years experience
MBCA Member, Southern Stars
1984 300D
1985 300CD

Good question. I think I would put in the correct sensor and wire it as the 84-85. Sorry about the confusion, I did not look at the year. (brain fart)


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Benzmac:
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM