Thread Rating:
  • 0 Vote(s) - 0 Average
  • 1
  • 2
  • 3
  • 4
  • 5
Modify an m104 tachometer to work with an om603?
tjts1 Offline
GT2256V
***


Posts: 120
Joined: Sep 2012
Location: The slums of Beverly Hills
#1
Modify an m104 tachometer to work with an om603?
The tachometer on my 87 300d died and I wasn't able to fix it. I have a spare 94 e320 cluster which I was planning to use parts from for the improved lighting. For shits and giggles I plugged the e320 tach into my 300d and it pegged at 7k as the engine was idling. The 300d reads rpm off the starter gear and the e320 reads off the 3 timing windows built into the flywheel.  Has anyone successfully modified a gas tach to work in a diesel? The car already has an M103/M104 flywheel from the 5spd swap so I guess one option would be to move the crank sensor or add a second crank sensor so it can read the 3 timing Windows. 

I appreciate any experience or ideals with the problem.

EDIT: Looks like one guy was able to do it on a 190d but I can't find any details. 
https://www.youtube.com/watch?v=iSLWW2ePaDg
[Image: 208104.png]
(This post was last modified: 01-09-2017, 10:27 PM by tjts1.)
01-09-2017, 10:18 PM
Find Reply
Tobulus Offline
GTA2056V
**


Posts: 98
Joined: Jun 2015
Location: Germany
#2
RE: Modify an m104 tachometer to work with an om603?
I did that once, wait till today evening when I get home
01-10-2017, 04:21 AM
Find Reply
maxypriest Offline
Holset
****


Posts: 259
Joined: Nov 2012
Location: Norfolk, England
#3
RE: Modify an m104 tachometer to work with an om603?
I used the W wire from the alt into a Dakota Digital devise and then into the tach.
Works for me.
W124 om606 HX40 finished and it's a beauty 450bhp/456ft-lbs
01-10-2017, 06:37 AM
Find Reply
Tobulus Offline
GTA2056V
**


Posts: 98
Joined: Jun 2015
Location: Germany
#4
RE: Modify an m104 tachometer to work with an om603?
You dont need any additional devices to connect a gasoline tach to either the generator or the engine speed sensor
01-10-2017, 07:09 AM
Find Reply
barrote Offline
Superturbo
*****


Posts: 1,248
Joined: Dec 2011
Location: Portugal
#5
RE: Modify an m104 tachometer to work with an om603?
talking in tacho´s .... odo´s shouldn´t be that hard too, anyone know how to hook a 616 gear box speed sensor to a w124 cluster? or the ABS speed sensor .....
thanks
FD,
Powered by tractor fuel
01-10-2017, 07:48 AM
Find Reply
Tobulus Offline
GTA2056V
**


Posts: 98
Joined: Jun 2015
Location: Germany
#6
RE: Modify an m104 tachometer to work with an om603?
Look at my project-thread for speedometer-informations

Here is information about tachometer-adjustment:

All the w124 tachometers I have seen shared the same board layout. Newer versions have a modern style, green board, the older ones have a brown board. But the layout is basically the same. They are all built for different rev signals, but basically the only difference is how many pulses the tachometer gets per crankshaft rotation. Also they are very tolerant to what sort of input signal you feed to it.

There are several resistors and capacitors on the board, you are looking for a small non-electrolytic-style capacitor. In the picture, it is shown in the lower right corner, the green one. This capacitor defines, how much the needle responses to each signal impulse. The higher the capacity, the greater the response. On this board, it is a 4.5nF capacitor for signal input from starter gear sensor (144 pulses per crankshaft rotation). As you can see, I soldered a bigger capacitor parallel to it to increase capacity by 47nF. I did this to modify this tachometer for signal input from generator terminal W.

   

The dimension of the components on these boards are different from version to version, I recommend to look for the smallest capacitor on the board.

There is also a variable resistor on that board to fine-tune the instrument. With this resistor, you can put an offset to the instument. This is for fine-tuning only.

Grüße
01-11-2017, 03:17 PM
Find Reply
tjts1 Offline
GT2256V
***


Posts: 120
Joined: Sep 2012
Location: The slums of Beverly Hills
#7
RE: Modify an m104 tachometer to work with an om603?
Grüße
Thank you very much, this is exactly the information I was looking for. Did you try multiple capacitor values before arriving at this solution? Do you think matching the capacitor value of the original 6k diesel tach would be a good starting point?

I think I found a burned resistor on the diesel tach so I'm going to try replacing that one, then give the gas tach another try if that fails. 
Cheers
[Image: 208104.png]
(This post was last modified: 01-12-2017, 02:44 AM by tjts1.)
01-12-2017, 02:43 AM
Find Reply
tjts1 Offline
GT2256V
***


Posts: 120
Joined: Sep 2012
Location: The slums of Beverly Hills
#8
RE: Modify an m104 tachometer to work with an om603?
I was able to fix the 6k diesel tach by replacing the 2 electrolytic capacitors and 1 burned up 51ohm resistor. The Caps are 50v 1uF and 100v 10uf. The 10uF cap was short circuited internally. There was no resistance across the 2 pins. The new caps are on the right and the blue resistor on the left. I used a 2w vs 1w originally. EDIT: I also replaced the little black diode in the upper left hand corner because I had one on hand. The new blue resistor still gets warm to the touch which is probably not good but the old 1w resistor survived 30 years so the 2w resistor I installed should last at least as long. 
[Image: NVIB48q.jpg?1]

After the fix I found that the tach was reading about 200rpm too low so I adjusted it with the potentiometer built into the circuit board.
[Image: 4jl9ONV.jpg?1]

While I had the 300D and E320 clusters apart side by side, I swapped the E320 outside temperature gauge and plug (mine was broken), light tubes for improved lighting at night and orange needles. Mine were faded to yellow.

[Image: 7n0dvCz.jpg?1]

Ignore the 7k tach lol
[Image: ctrwzjz.jpg?1]

Light tubes. These carry light from the back of the cluster to the front. They can be swapped out by drilling out the plastic pins holding them in place. The 87 one is on the left, 94 on the right.
[Image: FoMyylO.jpg?1]
[Image: 208104.png]
(This post was last modified: 01-16-2017, 08:22 PM by tjts1.)
01-16-2017, 08:17 PM
Find Reply
hents99 Offline
GT2256V
***


Posts: 128
Joined: Nov 2014
Location: Estonia
#9
RE: Modify an m104 tachometer to work with an om603?
Very good thread. 

Mercedes Benz (VDO) Outside Temperature Display Repair:


https://www.youtube.com/watch?v=CHpzMeb1L0c
------------------------------------------------------------------------
http://www.elbe.ee - MB performance parts. 
W201, C126, W463 STD, W140
01-17-2017, 02:56 AM
Website Find Reply
mrfajita Offline
Naturally-aspirated
*


Posts: 3
Joined: Apr 2016
Location: North Colorado
#10
RE: Modify an m104 tachometer to work with an om603?
This may be the answer to my tach problems, also Hents99 I may have to try to repair my temperature display as well
'77 300D, 617.912, HY35 15psi, 3" side pipe, maxed out stock MW pump
'87 300TD, 603.960, questionable mods from the PO including a ghetto 3" straight pipe
Today, 01:19 AM
Find Reply


Forum Jump:


Users browsing this thread: 1 Guest(s)