Add a Tach?

[Mark DiSilvestro]

I noticed some of the 300D cars had a tachometer. Is there a way to add a tach to my '82 240D?
Thanks

Happy Motoring, Mark

[rs899]

I am not sure it has been done before, but , in theory, it could be done on an '82 or '83 240D . The inductor that reads off the crank pulley is used on the 300D for the tach. This is used for pollution control on the late 340D. If you get the rest of the circuit from a 300D, it should be possible to create a tach on yours (if you disable the EGR). I do not believe anyone here has ever done it

[Mark DiSilvestro]

While with the PO, someone (probably his teenage son) pried the clear plate from the front of the instrument cluster, then crudely attempted to glue it back on. I thought I might pick a 300D cluster from a salvage yard, solve my 'glue' problem and, in the process, upgrade to a tach.
Well, my 09/81 240D does indeed have some sort of TDC sensor on the crank balancer, but of course the '82 240D wiring diagram in my Haynes manual doesn't show it. My Haynes does show a TDC sensor hooked up to an 'overload protection control' in the '81 300TD wiring diagram, but no tach circuit. So for now, my 240D will have to remain tach-less.
Regardless, many thanks for the info.

Happy Motoring, Mark

[ThosDoran]

Mark,

If you ever follow up on that sensor keep us posted.

I'd love to add a tach to my 240, even better if I can use one out of a 300D.

T

[Wallknight]

Good luck finding one from a 300D that actually works.

[ThosDoran]

Hmm, good point.

BTW, where are you in Western PA? Went to high school in Grove City. My sister still lives there.

T

[Mark DiSilvestro]

Originally Posted by Wallknight

Good luck finding one from a 300D that actually works.

I was looking at the owner's manual, just after I got this car last month. The page for the dash showed a tach but no details like '300D only'. I guess, for 'only' $20,000, one didn't get a tach or right side mirror on a 240D.

I might just go ahead and get that 300D instrument cluster anyway, just to get one that isn't glued together, though after removing the P O's supplemental duct tape, the damage on mine isn't too noticeable.
And I'll have some spares for the speedometer and other guages.
Then I can decide whether to install a non-functioning tach/small clock or stay with the 240D's large clock.

Happy Motoring, Mark

[mobetta]

maybe not quite what you are looking for, but here is an aftermarket diesel tach for $65. from what i've read you can order one w/ lighting, and they work well. doubles as an hour meter.

http://www.tinytach.com/tinytach/diesel.php

[winmutt]

Interesting. Couldnt you use the millivolt method of IP timing as a tach? ..... I'll have to look into this..

A pulse sensor attached to a GP that could calculate rpm based on pulse/60 ya?

[pleiades]

I guess, for 'only' $20,000, one didn't get a tach or right side mirror on a 240D.

My 300CD doesn't have a right side mirror either. It's a coupe thing, I think?

[dieseldiehard]

Originally Posted by winmutt

Interesting. Couldnt you use the millivolt method of IP timing as a tach? ..... I'll have to look into this..

A pulse sensor attached to a GP that could calculate rpm based on pulse/60 ya?

Nope! that won't work, you need to generate impulses from the crank/pulley and feed them to an instrument to display RPM

If you want a tach, buy all the stuff involved off a wrecked car and wire it up. I added one to my '79 300TD when I installed a turbo engine, its not a huge job.

The only thing I don't have is a working cruise control. If I ever get time I will install the electronic cruise instead of the vacumn cruise that was OE.

[mobetta]

the tiny tach uses a impulse from the inj. lines , similar to some diesel timing lites. for the money, i dont think it can be beat.

[winmutt]

Originally Posted by dieseldiehard

Nope! that won't work, you need to generate impulses from the crank/pulley and feed them to an instrument to display RPM

If you want a tach, buy all the stuff involved off a wrecked car and wire it up. I added one to my '79 300TD when I installed a turbo engine, its not a huge job.

The only thing I don't have is a working cruise control. If I ever get time I will install the electronic cruise instead of the vacumn cruise that was OE.

Why from the crank pulley? The cylinder is going to fire once per rev right? The GP is going to generate some juice due to heat (per millivolt method) right? I fail to see how it wont work.

[dieseldiehard]

Originally Posted by winmutt

Why from the crank pulley? The cylinder is going to fire once per rev right? The GP is going to generate some juice due to heat (per millivolt method) right? I fail to see how it wont work.

Fires once every rev? really?

Well, without going into the physics of how heat at the GP's is non linear parameter and varies according to external events (weather, how long the engine has been running, etc.) and what we want is a display that consists of an impulse meter that integrates engine revs into a linear (analog or digital) disply, its simple - it won't work. Or they would have done it already.

[Mark DiSilvestro]

Originally Posted by pleiades

My 300CD doesn't have a right side mirror either. It's a coupe thing, I think?

In the two salvage yards that I visited, the one 300CD at the first yard and all five of the 300D at the second, had come with right hand mirrors, though some were broken or had already been removed. I found no 240D in either yard. I would have gotten the RH mirror from that 300CD but it was damaged, so I got one at the second yard, from the same '84 300D that I got my driver's seat and back seat. Also, there was another 300D at the second yard that had an electrically adjustable RH mirror!
Incidentally, that 300CD color matches my 240D. Can anyone tell me if the W123 300CD hood and front fenders will fit a W123 sedan?

But for now, no more cosmetic stuff, as I must try to install the new upper control arms this week.

Happy Motoring, Mark