i've been trying to coax my tach to work. i've been through the archives listings mentioning the cigarette butt trick. i opened the round plastic thing on my '84 300D turbo and there was nothing in the top of the lid. it did not appear that anything was supposed to be plugged in there. (at least not in my car) i found a post leading me to that conclusion, but my question remains, what the heck is that thing for and what do i need to do to make the tach work?

It sounds like you got the cover off, but you did not pull the tach sending unit out. Pull on the piece that is under the cover. once you pull it off you will see the pin connections.

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2001 Dodge Ram 2500 Cummins Turbo Diesel - 4x4, auto, 3.54 gears, long bed
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'92 300D 2.5 Turbodiesel - sold
'83 300D Turbodiesel - 4 speed manual/2.88 diff - sold
'87 300D Turbodiesel - sold
'82 300D Turbodiesel - sold

Apparantly someone has removed the tach sender unit from the case. If it is completely empty that has to be the case and you will have to purchase a new sening unit.

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Richard Seaman
1982 300D Turbo 198k
1987 420SEL Sold
1993 400SEL 123k
MBCA Desert Stars

i checked my performance products catalog and it lists the tach sending unit, but only up to '83 models. this leads me to believe there is something different going on in my '84. can anybody confirm?

my tach is still working after a month, after I cleaned connections put dielectric on them and a heavy rubber washer on top the unit before screwing the cover back on I also pray over it if it flutters.....
William Rogers....

[Edited by william rogers on 03-19-2001 at 08:22 PM]

84 and 85 300D/SD have "nothing in the top of the lid". I find only a female connector with a cap.

David

thanks for confirmation. i wonder what that female connector is made to plug into. what should i do to try and fix the tach on this car?

someone has removed the unit under the cap, looks like all you have to do is buy that unit and plug it in ,I think they sell them on the parts section of this web site.I belive that the plug is also used to plug in a dinostic
machine.
William Rogers.......

T.D.C. Sender Unit part # 001 153 84 28 @ $32.27 ea.

From FastLane...

The TDC sensor is in the engine, and sends pulses to the TCD sender which converts them to RPM for the tach. Otherwise, the plug can be used by a MB dealer to plug into their diagnostic computer.

Replace this part, and your tach should work.

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Scott Longston
Northern California Wine Country...
"Turbos whistle, grapes wine..."

thanks for your help. i'll give it shot.

OLD TOPIC, NEW TWIST.

I have read the numerous post on tach repair. I will check out the sending unit for loose pins, and try to butt and/or washer trick. However, the problem my car has is that the RPM reading goes to "0" when I put the tranny in reverse In all the other gears (PARK included), the tach seems to be working fine, although at times it is a little slow to respond. Is there some type of sending unit or connection on the tranny that I need to checkout?
The car is an '83CD-T. Thanks for your help.....

Marks88

When I was driving my car in reverse, the speedometer went to zero too, shouldn't the techometer be the same way?

David

be459,

What type of vehicle do you drive? I always thought that it would not matter, which gear the car was in, that the tach still should register positive RPMs.
I have two other vehicles, '97 Camery and '88 300E. Both car's tachometers maintain positive RPMs through any gear selection. I have had my 300 CD-T only few weeks, maybe I've just noticed the "0 reverse thing", recently. Is this a standard thing with 300 CDS?

Marks88

Mark,

It is just a theory. When I am driving my car in reverse, I am looking at the street thru the rear window and cannot see the speedometer or the techometer.

David