For a long time now the tachometer on my 300 TDT works intermittently.
When it does work, it works perfectly. Sometimes it will work for
hours, sometimes it will not work for hours, sometimes it will work for
just a few minutes and then stay dead for a long time and vice versa.
I know about the ribbed small barrel shaped unit on the drivers side
fender under the hood and also the sender unit that is down by the
front crankshaft pulley.
Does anyone have a guess as to which one of these is the likely
There is no apparent pattern to the problem. Bumps don't affect it or
anything else I have been able to notice. Once when I used a pressure
washer under the car it came on when I started the car afterwards and
it had been dead for a while before that, but I haven't been able to
repeat that, even when I really targeted the sender for cleaning.
This was addressed in an earlier thread, the guy with the
winning answer said to pack some material, [foam]? under the
cap thing on the fender. Trying to remember..., take the
cap off, and somehow the thing it screws down onto needs
lifted up, ie. the foam under it. now you screw the cap
back down, and the connection is made better somehow.
Worked for a bunch of us!! Good luck.. -Gar
Very high probability it's the ribbed barrel thing, which is called the
tach amplifier. Not sure exactly what's in it, but it's likely no
more than a transistor or two and a couple of caps. Like most of the
rest of the electronics of this vintage, it ain't worth crap. And when
it goes, it leads to erratic tach behavior. In fact, I need one
myself, as mine is starting to act up. The original lasted about 22
years, the replacement from MB maybe 4.
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