Gasser tach in a diesel? - PeachParts Mercedes-Benz Forum

pizzachef · #1 09-21-2007, 08:00 AM

I found a tach/clock combo from a w126 gas powered car and was wondering if its the same as the diesel version? I don't have a tach (I have the sensor and a round thing to plug something in to), so I'm getting a tach amp and the wire leading from it to the cluster from a diesel, but the gauge is from a gasser and before I commit to buying it I wanted to make sure its gonna work.
Thanks for the help,
-Geoff

mbdoc · #2 09-21-2007, 08:12 AM

MB designs their tachometers for the number of cylinders.

A V-8 won't work correctly in a car that has a different number of cylinders.

pizzachef · #3 09-21-2007, 09:30 AM

Quote:

Originally Posted by M.B.DOC

MB designs their tachometers for the number of cylinders.

A V-8 won't work correctly in a car that has a different number of cylinders.

I'm guessing this is for gas powered cars then...so the tach gets the signal from the distributor or something in the ignitioin system as vstech said?

That's good to know...I'll stay on the lookout for a diesel tach then.
Thanks,
-Geoff

Mustang_man298 · #4 09-21-2007, 11:56 AM

Typically gasoline tachs operate by reading voltage pulsations from the power wire going into the primary (low voltage) side of the ignition coil, which sees an inductive voltage spike every time the coil secondary (high voltage) side is fired.

The diesel tachs are set up to read in a similar way, the crank sensor generates a millivolt pulse every time the balancer pin passes by, which is fed to the tach amp that sends an amplified signal to the tach, I don't know if they are interchangeable.

Also one other thing you should know, you say you have the sensor there going to a round plug, but don't origionally have a tach. MB did this on some of their cars for diagnostics, the good thing is you have a sensor bracket and balancer pin. The sensor however will need to be modified or changed. The actual sensor is the same, but the round plug on it is different than what you will need, I have pics somewhere of each, but the plug you need is (trying to remember) either going to be oval or half round, to fit into the tach amp with the other amp plug. You will also need to get a tach amp and bracket for it. Also beware the tachs and amps have 2 different types, depending on year, (I want to think 85 was the cutoff year) they changed when the cars got computerized. I just went thru this process myself for the 82 I'm rebuilding.

pizzachef · #5 09-21-2007, 01:23 PM

Thanks for the tip on the connector...I'll have to make sure to get the sensor connector from the donor car as well. As for a bracket, I have a round thing with a cover on it that looks like where the amp would connect to, its at the bottom of the photo below, near the center. So I'm assuming I can get the amp and screw it onto this round receiver, and run the wire from the receiver to the cluster...and now I'll have to make sure to get the sensor connector from the donor car so it fits in the receiver with the cluster wire connector. And I'll probably have to run a power wire somewhere as well. I think I saw a pinout of the amp on here somewhere.

Once I get all the bits and pieces I'm hoping its not too difficult, I'll post my results.

toomany MBZ · #6 09-21-2007, 07:50 PM

Quote:

Originally Posted by pizzachef

Thanks for the tip on the connector...I'll have to make sure to get the sensor connector from the donor car as well. As for a bracket, I have a round thing with a cover on it that looks like where the amp would connect to, its at the bottom of the photo below, near the center. So I'm assuming I can get the amp and screw it onto this round receiver, NO this will not work! and run the wire from the receiver to the cluster...and now I'll have to make sure to get the sensor connector from the donor car so it fits in the receiver with the cluster wire connector. And I'll probably have to run a power wire somewhere as well. I think I saw a pinout of the amp on here somewhere.

Once I get all the bits and pieces I'm hoping its not too difficult, I'll post my results.

This pic is NOT a 126, (SD). You have a newer system (85) with the small cap. Nothing connected in there. Set ups are different. This is electronic, the tach amp of which you speak is mechanical, they do not interchange. Sending unit is on trans, I think. Good luck BTW.

lietuviai · #7 09-21-2007, 11:04 PM

Quote:

Originally Posted by pizzachef

I see ABS in your car.

vstech · #8 09-21-2007, 09:22 AM

the diesel tach does not care how many cylinders it has, it counts the revolutions from the crank. I do not know if the gasser uses the same method, or if it gets it's signal from the ignition system.

vstech · #9 09-21-2007, 01:31 PM

sheesh!
you have an 85, and a euro... putting in a tach is going to be a challenge. you are gonna need the harnes for the tach itself, as the 85 used a totally different scheme for tach wiring, the euro of course had none at all... find a donor that already has a tach, and pull all the stuff of of it...

toomany MBZ · #10 09-23-2007, 09:30 PM

Quote:

Originally Posted by pizzachef

I found a tach/clock combo from a w126 This is where I got confused. gas powered car and was wondering if its the same as the diesel version? I don't have a tach (I have the sensor and a round thing to plug something in to), so I'm getting a tach amp and the wire leading from it to the cluster from a diesel, but the gauge is from a gasser and before I commit to buying it I wanted to make sure its gonna work.
Thanks for the help,
-Geoff

Your sig, however explains the rest, sorry. I guess you will need the amp after all. IIUC, don't think that cluster will work, as it's electronic, meaning it gets the signal from somewhere else, different plug in back, if you can, get a tach from an early 123. After all that, should work.

mbdoc · #11 09-24-2007, 08:42 AM

You could use a 1984 300DT system tachometer, as they only used a crank sensor & NO EGR computer. The tach read directly from the crank sensor.

I believe the part number for the 1985 tach/clock was the same.

toomany MBZ · #12 09-24-2007, 03:10 PM

My '84 has no amp, the tach works, my '83 has an amp, which I replaced, now that works also. There are two different gauges, with two different hook ups. I removed the cluster from my '82 300 DT, (amp) on the rear of the tach the plug in is a two prong affair with the #230/107/10 with 6000Imp underneath. I have another tach from an unknown car, it has a three prong plug, the middle prong is just plated through, leading me to believe it is a ground, and the #902/74/1 with 14000 Hz underneath. Both of these gauges are clock/tach. I have not pulled the cluster from my '84. I also have a cluster from a 126, the year printed on the back is '83, it has a two prong plug with the #902/29/5 with 6000Imp underneath.

Mustang_man298 · #13 09-24-2007, 11:51 PM

Quote:

Originally Posted by toomany MBZ

My '84 has no amp, the tach works, my '83 has an amp, which I replaced, now that works also. There are two different gauges, with two different hook ups. I removed the cluster from my '82 300 DT, (amp) on the rear of the tach the plug in is a two prong affair with the #230/107/10 with 6000Imp underneath. I have another tach from an unknown car, it has a three prong plug, the middle prong is just plated through, leading me to believe it is a ground, and the #902/74/1 with 14000 Hz underneath. Both of these gauges are clock/tach. I have not pulled the cluster from my '84. I also have a cluster from a 126, the year printed on the back is '83, it has a two prong plug with the #902/29/5 with 6000Imp underneath.

The two pin one is the earlier style and what he needs, the 3 pin is the newer integrated one for computerized setups.