Diesel tachometer question.

- B
- Bernard Farquart
  
  Contact options for registered users
posted
19 years ago

Tue, Oct 12, 2004 6:03 PM

I am hoping someone can answer a little question for me.

I have a w116 chassis 300sd, the tach worked very rarely, so I found the little round screw-off thingy in the engine compartment and un plugged the top portion, cleaned off the pins with 1500 grit sandpaper, put dielectric grease in the female side of the connector and now have a tach 80% of the time. (I think I need to repeat cleaning)

My girlfriend has a w123 chassis 300d, and when I unscrew her round thingy in the engine compartment, there is no top part under the cover! I only see the female connectors, no plug in part at all. (she has never had a working tach in the eight months she has owned the car)

Is she missing part, or did they change the way things were done in between the two cars?

what do you call that?

Thanks for any help

Bernard

- B
- Bill Pelka
  
  Contact options for registered users
Vote on answer
posted
19 years ago

Tue, Oct 12, 2004 9:58 PM

Greetings,

Depending on the year of your girlfriends car, the fix for the tach can be as simple as a blown fuse behind the glovebox. I have a 1984 300D Turbo with CA Emission Package. If you remove the 2 piece clips that hold the glove box in place, about 8 of them, with a small screw driver blade. Then pry the glove box light out of the way. Remove the glovebox "Box", and that will expose a few relays and black boxes. If you look all the way to the right, you will see a small box with a 10 amp spade type plug in fuse on it. Chances are good that this fuse is blown or maybe just "crusty". BEFORE you button up the "Box", check it out. If that fixes it, button it up and enjoy.

If that is not the problem or the car is of a different build date, repost and maybe we can supply you with a different fix...

=====================

As for your Tach, I have read that you can put a filter from a cigarette to help "shim" downward pressure on the plug. This gives you a tight fit and eliminates an intermittent connection.

-------------------------------

Or it could be the sender...

Bill

- R
- Richard
  
  Contact options for registered users
Vote on answer
posted
19 years ago

Thu, Oct 14, 2004 4:28 PM

I call this a "tach amp" and you need two of them.

I messed around with mine for years cleaning it, fixing it, finally I bought a new one. Save yourself the hassle, get a new one. They always work and at some point you do get sick of fixing them and staring at a dead tach needle.

I know in the past I've recomeneded dialectric grease on tach amps. That was a mistake; in retrospect it never did any good, in fact possibly the opposite. It is an insulator after all.