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Discussion Starter #1
Hi all. Quick question. Is there a way to wire up a tach. I like the look of the tach with clock in it, instead of the hugh clock. I have an 81 300d. Thanks for the help.
Matt
 

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You'll need a few items. You may have the gray sensor wire from the front crank, but it probably ends in a plug you can't use.
In the pics you may be able to determine what plug end you need to plug into the bracket that holds the tach amp, new ones are available, and the wiring harness that goes to your "new" instrument, this one I don't know about this one. Also, said tach will need the two prong plug on the back, as in pic.
The white car is an SD, '83 with the old style amp, what you need.
The last two pics are from my CD, '84 that has the new style, note no amp. But the 123 has a different bracket, the one you need.
 

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I'm not seeing a wire by the crank. Do you know which side it should be on? She's been taking an oil bath so she's pretty dirty. Is the tach amp the square plug on the bottom of the first picture? I've already scrounged up the tach at the salvage yard and it's got the same plugs as your picture. Will probably take your pics out there with me and try to get the amp and plugs. Thanks.
 

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No, that is not the tach amp, it screws into that round plug that has the female ends. I'm not sure what that square coupling is. The magnetic pick up is on the drivers side near the vac pump, as you're aware, it's covered in "gunk". It's a gray wire, the other end of which you can see going to the bottom of the round receptacle.

This link is for the sensor wire... Select Brand

Tach amp... https://www.autohausaz.com/search/product.aspx?sid=fss0zo45xnm5ko45j3cfxcv2&[email protected]&[email protected] &year=1983&[email protected] & Vacuum&[email protected] Control Sensor

These amps fail routinely, so a used item may not work, or not for long, there are temporary fixes. They are getting more expensive by the year! I bought one 14 months ago, about $70 then.

Your biggest concern is going to be the wiring harness from the bottom of the amp, to the tach itself.

I'll take a pic of the crank sensor, have one in the other computer, later.
 

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I recently replaced the oil pump, helical drive gear, and its retainer bushing/sleeve on my '81 300D. According to my FSM - there's an adapter you can use that threads into the helical drive gear retainer, so that you can use a mechanical tachometer. This may be an alternative to finding the tach setup from a turbodiesel model...

I would also love to have a tach, but can't seem to find any turbodiesel donors anywhere near me. :(
 

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You also forgot that he will need a new harmonic balancer with the stud for the pickup.
 

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Discussion Starter #7
Did the 300D's come with the pickup? I'm thinking that it doesn't have it, not seeing any wires by the vacuum pump, which throws another wrench in my plans. I'll take another look tommorow. Thanks for all the help!
 

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Hopefully not, my 240 had that sensor wire from the crank, no tach, different plug at end, almost a speed-o type.
Not the wire, the stud that sticks up from the balancer at zero degrees that the sensor reads.
 

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Not the wire, the stud that sticks up from the balancer at zero degrees that the sensor reads.
Is there any chance that someone could post a pic of this?
 

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This pic shows that pin, I used white out on the end, have cleaned it off, tach is operating as designed.
Hope this helps, not sure if the 240 had that pin.
 

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AFAIK its not, this is what prevented me from adding it to my Euro NA. Now, that doesnt mean you cant pull the balancer get a stuf welded on and have it re balanced.
 

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Do you have any idea if the balancer from a turbo 617 would fit the NA 617?
Ah yes it should but I believe they are balanced to the specific crank shaft. Could be wrong.
 

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I just looked at my NA OM617's harmonic balancer. It *has* the stud, just as pictured in Rmac58's post above. I guess now it's just a matter of finding the tachometer, crank sensor, amp, and related wiring. :)

It will be nice knowing how fast my engine is spinning when I'm on the freeway.
 

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Can anyone post a pic of where the crank sensor plugs in? Does it plug into the amp somehow?
On the right side of that round plug, female pin #'s 7, 8 and 9, can just barely make 'em out. The gray lead coming up from below ends in that section, the amp, lower left "trash can" looking thing connected via a plastic strap, plugs in, connecting the two.

My previous answer, was thinking the cluster vs the balancer, sorry.
 

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hi guys
can anyone help me to test my tach on 1985 300SD,is there a way to test tach
the rpm sensor ,i am all confused,i got a pick up at eng/trans flange and a pick up at the crankshaft pulley is there a way to do individual test to find out wich one is driving me insane
thanks guys
michael
 

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hi guys
can anyone help me to test my tach on 1985 300SD,is there a way to test tach
the rpm sensor ,i am all confused,i got a pick up at eng/trans flange and a pick up at the crankshaft pulley is there a way to do individual test to find out wich one is driving me insane
thanks guys
michael
That is a different pick up sensor, in post #2 third pic down, that is my '84 CD, same set up as an '85. Note the small cap covering the plug. On the white car is the old style, an amp is involved. The sensor wire for the new style comes off the transmission.
Edit: I don't know how to trouble shoot the new style tachs. But here, the second one down, is the sensor wire for it. http://catalog.worldpac.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.mercedesshop.com/&cookieid=2AE0BZRXJ2AU02UXE3&year=1985&make=MB&model=300-SD-002&category=All&part=RPM+Sensor
 
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