PS..How I fixed my tachometer... no tools needed!
 

1982 300D White 200K+(?)

I forgot to mention how I fixed my tach with no tools. I also learned this from the MBZ.org site. I removed the sending unit under the drivers side hood on the fender by unscrewing by hand. You now must separate the screw cap from the sending unit. The video from repairFlix.com says you have to saw the top off, but I have done this with 3 different ones this week and needed only hand pressure to separate the top (this made me very popular at my MB club this weekend... fixed 2 of 3 tachs this way!!!)
With a bit of coaxing and twisting, the cover of the sending unit comes apart revealing a layer of white silicone stuff which protects the circuits.

The "fix" consists of placing a bit of sponge or foam in the cap (a cigarette filter was suggested...) thus providing extra pressure on the pins when screwed down. This fix may work for one of two reasons... either you have a cold solder joint under the silicone, or the contacts are improved by the pressure. Either way it will work or it won't.... Hope it does for you, it did for me.

Thank you all for listening.

Mr Goodfahrt

Non-smoker tach fix....
 

I couldn't get foam to exert enough pressure on mine.

You don't have to smoke or find (and/or touch, yuk!!) a cigarette butt if you use one of those yellow, 3M brand, wire nuts under that cap.

I used the insert as a pattern to cut a circle of corrugated cardboard which I placed between the cap and the circuit board. When I put everything back together I gave the pins a quick shot of contact cleaner and it worked perfectly thereafter. I kept a couple of spare cardboard circles in my toolbox for when the one in the car lost its tension.

There was a long thread on the butt trick several years ago, I did it on my SD but it will quit again and again,some people take them apart and resolder cracked solder joints .I ended up just getting a new unit from FastLane as I like having a working tach...........
William Rogers.......

tac
 

yes, I did the butt and foam trick and it works sometime..I will just get a new one..

can somebody post the part number of this sending unit?

I'm thinking of placing a tach on my diesel ride, (since it doesnt have one). What other things do i need aside from the tach/clock and the sending unit??

a piece of cork cut from a wine bottle stopper worked great for me.i was able to slice the cork in different thickness to get the size that worked best.the fix left me a little intoxicated

I fixed my tach too. It's a cheap, temporary fix, but putting a chunk of styrofoam on the top of the silicone surrounding the pins and dabbing some dielectric grease on the end of the pins has made the tachometer last longer than it ever has as I can remember, which is 2 days. I'll post later on updates if needed.
-Joe

The only permanent fix is to re- solder the connections on the trace side of the board.