Add a Tach? - Page 2 - PeachParts Mercedes-Benz Forum

bgkast · #16 10-09-2006, 08:14 PM

VDO and other manufactures have a tach that receives a signal from the alternator. These would work on these engines, but they must be calibrated and they will not easily fit in the stock location

winmutt · #17 10-09-2006, 08:27 PM

Quote:

Originally Posted by dieseldiehard

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.

Ok. I'll get back to you

mobetta · #18 10-09-2006, 09:29 PM

Quote:

Originally Posted by Mark DiSilvestro

Incidentally, that 300CD color matches my 240D. Can anyone tell me if the W123 300CD hood and front fenders will fit a W123 sedan?

Happy Motoring, Mark

AFAIK, all 123's are the same front clip, the CD's have longer doors, and the TD's and Long sedans have longer rear doors.

Mark DiSilvestro · #19 10-10-2006, 12:09 AM

Quote:

Originally Posted by bgkast

VDO and other manufactures have a tach that receives a signal from the alternator. These would work on these engines, but they must be calibrated and they will not easily fit in the stock location

I think I'd just get a 300D instrument cluster, rather than try to find someplace to stick an external tach. Then I'd also get an undamaged cluster housing, and spare speedometer parts, in case my current speedometer repairs don't last.
I might take another look at that coupe fender too, as my right front is starting to re-rust through the PO's bondo job.
But first - those upper control arms.

Happy Motoring, Mark

rs899 · #20 10-10-2006, 07:31 AM

Mark-

The 300CD fenders will fit fine, but the earlier W123s (not sure when the cutoff was) had their fenders "glued" on by the wonderful undercoating they used on the bottom. You will need to have them torched off, probably ruining the paint. The later cars had a plastic inner fender and no goo- so they come off without a fuss.

Rick

WD8CDH · #21 10-10-2006, 10:55 AM

Quote:

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.

It's every other revolution but the big problem will be the very tiny signal will be next to impossible to detect. It would be much easier to buffer the signal from the rpm sensor on the crank pulley.

Mark DiSilvestro · #22 10-10-2006, 07:16 PM

My 240D already has a crank sensor.It would be nice if the harness is already set up for a factory tach, but without a wiring diagram, I just don't know.

Happy Motoring, Mark

SUNRG · #23 10-19-2006, 08:24 AM

Quote:

Originally Posted by 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

which transducer size should i order for my '81 240D - 6mm or 1/4"?

does anyone have a picture of an install location?

i want to get two of these one for my 240D, and one from my TDI - just for the hour meter feature for tracking maintenance intervals.

TIA & cheers

SUNRG · #24 10-21-2006, 10:30 PM

Quote:

Originally Posted by SUNRG

which transducer size should i order for my '81 240D - 6mm or 1/4"?

FWIW - '81 240D = 6mm transducer

mobetta · #25 10-22-2006, 12:55 AM

if all you want is an hour meter, go to napa.

WD8CDH · #26 10-23-2006, 08:36 AM

If you get a cluster from a 300, you will probably have to swap in the speedo from your 240 to keep it accurite. The 300 has a different rear end ratio from the 240

Mark DiSilvestro · #27 10-23-2006, 06:43 PM

Quote:

Originally Posted by WD8CDH

If you get a cluster from a 300, you will probably have to swap in the speedo from your 240 to keep it accurite. The 300 has a different rear end ratio from the 240

That's good to know, as I'm now considering the possibility of swapping in a 300D differential, to tone down the roar my 240D makes at 65 mph! There's a blue '80 300D down the street that the owner wants to get rid of. He's offered it to me for free if I'll get it out of his driveway. The body looks good, exept for the L F fender which the owner replaced and is still in primer. Unfortunately, it's been sitting 5 years since the tranny died. In addition to the usual problems from sitting too long, water leaks have eaten up the floors/sills under the front seats. This morning I went to have a closer look at the car. The floor/sill on the driver's side had been crudely patched and needs to be re-done. The passenger floor looked OK but when I tugged on it, the passenger seatbelt anchor ripped right out of the sill! The engine isn't frozen but lord knows what sort of horrible sludge is now occupying the diesel fuel injection system. And of course it has the dreaded Chrysler climate control servo! So I'm wondering if it's even worth fixing up or should I just grab it as a parts car?

Happy Motoring, Mark

DeliveryValve · #28 10-23-2006, 07:58 PM

Quote:

Originally Posted by Mark DiSilvestro

That's good to know, as I'm now considering the possibility of swapping in a 300D differential, to tone down the roar my 240D makes at 65 mph! There's a blue '80 300D down the street that the owner wants to get rid of. Mark

I believe you would still have to match the speedo with the differential. The auto trans W123 300D 1980-81 used a ratio of 3.46/1 and they usually didn’t come with a tach in the cluster. The 300D Turbo which does have a tach in the cluster from 1982 thru 1985 uses the ratio of 3.07/1 and some in 1985 use a ratio of 2.88/1. But correct me if I am wrong.

Richard

Mark DiSilvestro · #29 10-24-2006, 12:01 AM

Quote:

Originally Posted by rmarzan

I believe you would still have to match the speedo with the differential. The auto trans W123 300D 1980-81 used a ratio of 3.46/1 and they usually didn’t come with a tach in the cluster. The 300D Turbo which does have a tach in the cluster from 1982 thru 1985 uses the ratio of 3.07/1 and some in 1985 use a ratio of 2.88/1. But correct me if I am wrong.

Richard

Well, I was thinking (and this is starting to get complicated now!) that I could remove my 240D's 3.69 differential and speedometer, then swap in the '80 300D's 3.46 differential, with it's matching speedometer (Don't want to kill all my power with the 2.88 or 3.07 gearing) then I could swap in the tach & clock instrument from an '84 300D turbo.
I would still need to know if the '84 300D tach will work off the 240D crank sensor, and if the 240D's instrument harness is even wired for a tach, and if not, what I would need to add as far as tach wiring or any other control unit or circuit to make the tach functional. Or should I just leave well enough alone?

Happy Motoring, Mark

DeliveryValve · #30 10-24-2006, 12:20 AM

Quote:

Originally Posted by Mark DiSilvestro

then I could swap in the tach & clock instrument from an '84 300D turbo.
I would still need to know if the '84 300D tach will work off the 240D crank sensor, Mark

Just make sure that the '84 tach is not from a California Version vehicle... They have three prongs and is controlled by a so-called computer through a sensor of the flywheel.