Referencing this thread: Mechanical to Electronic Speedometer Conversion

I am in the process of doing an OM606 swap and then a 722.6 swap. I am getting all of my ducks in a row so there are little to no surprises when I do the swap.

The 722.6 does not have a mechanical speed output so the speedometer will need to be swapped for an electronic version. I have an ASR speedometer from a W124. The ASR isn't a big deal if you do not care about a useless idiot light that will never light up(unless you wire it for something else).

The speedometer is fully electronic. I need to determine how the 400E's speed output works any knowledge will be beneficial to me and any other W124 owner that does a 722.6 swap.

I will be going back to the junk yard to figure out the 400E in a week and grab any and all parts necessary.

OK, I think this is your answer. I found what I was looking for in the wiring diagram for the 380SL. In a completely different file, I found the following.



The white and brown wires from the impulse transmitter (aka VR sensor) go directly to the speedometer module and connect on pins 1 and 2. I don't have a spare cluster to look and I don't have a picture of the back of the cluster, but my memory is that there is one connector with 2 pins and another connector with just 1 pin, which I would take to be the VR sensor and the output to the cruise control respectively.

Assuming that they didn't change things substantially between 85 and the year of your donor cluster, I'm quite certain you'll find a two pin connector with white and brown wires.

You should have the VR sensor on your transmission, so it's as easy as running a couple of wires.

You can easily test it on the bench by using my test setup - Mechanical to Electronic Speedometer Conversion



If you use a hole saw like I did as a test platform, just be careful.

Attached Thumbnails

 

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Current Stable

• 380SL (diesel)
• Corvette C5
• Manx
• Baja Bug
• F350 Powerstroke
• Auburn Boattail Speedster replica

Here is more information for you. The image below is the transmission wiring harness on a 380SL. A is the VR speed sensor, G is the connector to the cluster.



Toward the bottom of this page MBenz engine swaps you'll find more info.

My guess is you'll find something very similar when you dig into your donor car... if you even need to, I think you said you had the connectors.

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Current Stable

• 380SL (diesel)
• Corvette C5
• Manx
• Baja Bug
• F350 Powerstroke
• Auburn Boattail Speedster replica

On my 606 swap I opted to use a very low mileage rebuilt 300SDL trans, which has the electronic signal generator in the tailshaft. I'm planning to run an E420 speedo head along with a Dakota Digital signal calibration box to configure the speedo for my 2.65 diff ratio.

Nice solution.

The brown and white wires come from the VR sensor on the transmission - any idea what that black-red wire is for/from?

Attached Thumbnails

 

__________________
Current Stable

• 380SL (diesel)
• Corvette C5
• Manx
• Baja Bug
• F350 Powerstroke
• Auburn Boattail Speedster replica

Nice set-up, you could actually have a speedometer that reads correctly instead of MB-style overtly optimistic type

Has anyone considered just putting a small electric motor to spin the mechanical speedometer in proportion to that coming out of VSS?

Brilliant! I should probably be able to do the same once I figure out the 722.6

FSM indicates that it goes to Fuse #5 in the fuse/relay box

Power lead and another brown for ground? My gauge has an ASR light so there is an additional plug but its essentially the same gauge. I have the center plug with a single green line and then the same plug to the left like yours.

Mine has ASR as well. The green line to the center post is for the Hall sender (cruise, outside temp, etc.)

Which should be the same connector on the '87. Nice, this jut got a little easier in my mind.

you can also swap tailhousings on the transmission if its from a similar gen trans. I did it on a 123 trans for a 126 and will do it to my w124 trans for my w126

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1981 300SD 512k OM603

Speed sensor from the 400E transmission. I traced out the wiring and the sensor leads to a massive plug behind the ash tray and then smaller gauge tan and while wires go to the cluster where in the plug the tan and the second tan wire that matches with the black/purple with red dots are soldered together for the ground. The white and black/purple/red go to their respective pins on the gauge.

So, looks like all I have to do is take the black/purple/red and feed it to fuse #5. Fabricate some sort of mount for the sensor, and weld or use some super strong adhesive and set up the triggers on the driveshaft




Hmmmmmm. The diameter is 22mm



Speed sensor from a 400E. The diameter of the O-ring is 23mm and it would mount perfectly in the above hole if it were to be bored out and the post drilled and tapped for a bolt.

Now the question is what is behind the metal of the case. If anyone knows let me know before I decide to go to the junk yard, pull a 722.6 and take it apart.
--update--

Looks like I wont have to go take a transmission apart



http://www.bulkpart.com/Merchant2/graphics/Catalog-pdf/722-6.pdf

There is a trigger wheel!

http://www.youtube.com/watch?v=iB50x9VmhB8
My Russian isn't up to snuff but towards the end of the video, 4:36, the case of the transmission slides right off when the nose is flat on a surface. Leaving the clutches, drive gears, etc in place on the input shaft.

INTERESTING!!!

Here's a thread that may help with some ideas.

Mechanical to Electronic Speedometer Conversion

Here's my bracket and driveshaft "trigger wheel"





Note, I've swapped out the transmission such that I don't need the external bracket any more, but I left the driveshaft alone, in case I ever need to switch back to the original tranny.

__________________
Current Stable

• 380SL (diesel)
• Corvette C5
• Manx
• Baja Bug
• F350 Powerstroke
• Auburn Boattail Speedster replica

Thats my plan B if there isn't a trigger wheel on the end of the transmission. I'm trying to make my 606/722.6 swap look factory.

I'm also certain the sensor goes directly to the spedo with no computer before the gauge. Looks like I'll have to bench test it with a 12v battery and make a trigger wheel


I think what I've found is the park gear.