Installing an aftermarket tachometer on my 1986 250TD

[Romans 250TD]

Good Day.
My 1986 250TD wagon's instrument cluster has a large clock where the large tachometer with a smaller inset clock normally goes.
What's involved in adding an aftermarket or better yet factory tachometer in my diesel vehicle? Does anybody have a list of parts that I need to acquire or is it not worth the effort? I must own the only 5 speed manual vehicle with no tachometer. I'm at a loss with how to hook one up as my vehicle doesn't really have a distrubutor as with fuel injected gasoline vehicles.
Thanks in advance, Roman

 

[jberks]

Hi,
I can't tell you where to hook it up, but we put one into a 250 petrol back in 1980 and you will need to change the plastic screen in front of the clocks as the clock/tacho unit has a setting knob that comes through (like the speedo) and there won't be a hole for it. Though I guess you could always drill one. I suspect the wiring is already there, as it tends to be with these things.
Just thought - is this a 123 or later ? They changed around '86 and I don't know the later one.

 

[Arnie]

The tachometer on Diesel cars uses an inductive sensor on the front engine crankshaft pulley. The sensor is fitted on a small bracket and registers a notch on a thick disc behind the pulley as it rotates. I don't know if this sensor is used for other things too (possibly idle-speed control on the later, electro-mechanical injection pumps), or if it's just for the tacho. If just for the tacho, you may need to fit the whole lot- not expensive, but probably a bit fiddly. The notched disc and the bracket should already be there, but you will need to add the sensor, the wiring and of-course a Diesel MB tacho (petrol tachos are calibrated for 4 or 6 cyl engines and work a bit differently, as you mentioned.)

 

[numbnuts]

The tachometer on Diesel cars uses an inductive sensor on the front engine crankshaft pulley. The sensor is fitted on a small bracket and registers a notch on a thick disc behind the pulley as it rotates. I don't know if this sensor is used for other things too (possibly idle-speed control on the later, electro-mechanical injection pumps), or if it's just for the tacho. If just for the tacho, you may need to fit the whole lot- not expensive, but probably a bit fiddly. The notched disc and the bracket should already be there, but you will need to add the sensor, the wiring and of-course a Diesel MB tacho (petrol tachos are calibrated for 4 or 6 cyl engines and work a bit differently, as you mentioned.)

Why would you want to fit a tachometer to a diesel especially a merc diesel its not as if you are going to blow your engine because the pump is governed, its not a racing car so you don?t have to keep the revs up to achieve performance so why go to all that bother of fitting one not unless you are a boy racer in that case just keep it in the gears until you feel the car isn?t getting any more power then you know its time to change gear never mind about fifth gear your engine won?t reach maximum revs