Author Topic: Tachometer Drive  (Read 3366 times)

gcw206

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Tachometer Drive
« on: February 28, 2021, 16:05:43 »
Could not any information on this Forum.
I have a 1969 280SE W111 Coupe.
I have installed Pertronix Ignition, a stock MBZ "Red Coil" and resistor, and Bosch W9DC spark plugs.
All worked fine until a few days ago.
Sometimes (but not always) at right around 2000RPM, the tachometer will "jump" ahead.
I went to lube the cable drive, but found that there is no cable drive on this model.
I assume the tach is driven electronically off of the coil?
Where should I start the trouble shooting?

ja17

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Re: Tachometer Drive
« Reply #1 on: February 28, 2021, 17:23:02 »
Yes, yours is driven electronically off the coil. I am not sure if your conversion is causing the problem?
Joe Alexander
Blacklick, Ohio
1969 Dark Olive 280SL
2002 ML55 AMG (tow vehicle)
2002 SLK32 AMG (350 hp)
1982 300TD Wagon turbo 4spd.
1963 404 Mercedes Unimog (Swedish Army)
1989 flu419 Mercedes Unimog (US Army)
1998 E430
1974 450SLC Rally
1965 220SE Finback

gcw206

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Re: Tachometer Drive
« Reply #2 on: February 28, 2021, 18:51:38 »
No, she worked fine for over a year; this just started happening about a week ago.
Think I will check all of the wiring and the fuse situation, maybe something loose?

wwheeler

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Re: Tachometer Drive
« Reply #3 on: February 28, 2021, 18:59:08 »
I know when I had my 280SE tach rebuilt by Palo Alto, they added something to help reduce erratic movements. So possibly the electronics in the tach are going South. I would contact them and see what they say if you cannot find anything. These don't last forever.
Wallace
Texas
'68 280SE W111 coupe
'60 220SE W128 coupe
'70 Plymouth Roadrunner 440+6

gcw206

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Re: Tachometer Drive
« Reply #4 on: March 21, 2021, 12:38:20 »
Hello,
It was suggested that I might have a bad/loose ground somewhere in the tachometer wiring system.
I was advised to run a ground wire from the distributor housing to a solid ground, and see if that helped.
I did just that, and it seems to have solved the problem. 
No more erratic tachometer readings after about 6 hours of driving.
Thanks; this is a great site.
Galen

wwheeler

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Re: Tachometer Drive
« Reply #5 on: March 21, 2021, 13:50:04 »
Interesting. That was a good tip. Grounds can be one of the most difficult electrical items to troubleshoot.
Wallace
Texas
'68 280SE W111 coupe
'60 220SE W128 coupe
'70 Plymouth Roadrunner 440+6

gcw206

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Re: Tachometer Drive
« Reply #6 on: October 26, 2022, 18:33:05 »
Hello,
Update to the Update;
1.  The added ground did not do the job;
2.  Tach started jumping again;
3.  I checked all grounds, signal wire spacing, etc;
4.  I added a 10K-1W in line resistor to the tachometer signal wire (check out You Tube).
Works great (so far).
Galen

wwheeler

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Re: Tachometer Drive
« Reply #7 on: October 27, 2022, 02:40:32 »
If I remember correctly, Palo Alto speedo added a resistor to the tach when they rebuilt my W111 tach. I cannot be 100% certain, but seems like they made some alteration.
Wallace
Texas
'68 280SE W111 coupe
'60 220SE W128 coupe
'70 Plymouth Roadrunner 440+6