Hi all,

Although my day job has been crushing as of late, I've made petty good progress on my '87 300TD manual transmission swap.* Right now I'm down to the crank seal and my biggest question is what to do about the driveshaft. I fell out of touch with someone on the forum who may be able to hook me up with a preassembled rear-to-rear DS and I regret that. However, I just can't decide whether to (1) install a rear-to-rear driveshaft with a W201 flange, or, (2) have a new driveshaft made with a W124 flange. The 717.412 trans I'll be using already has a W124 output and, frankly, the price for a new one-piece driveshaft isn't as spendy as I thought.

But here's my first question: how do I get the reverse lights to work? The switch for the reverse lights seems to be in the manual shift mechanism, but there are no corresponding wires coming from the car. I think the reverse lights for the auto trans I removed are switched by the big, circular connection on the left side -- I'm sure someone will correct me if I'm wrong.

Second question: When I R&R the pedal box, how do I wire things to ensure pushing in the clutch disengages the cruise control? My wagon has working cruise and I'd like to keep it that way!

Appreciate the help -- funny thing, but even though I deal in words all day, I like pictures. By all means, snap and send photos if you think they'll help!

Corvo Gold

*What will make your life easier when removing the trans without a lift are SUV jackstands and an ATV jack. I already had both since they're great for R&R'ing flat engines (see userID for more details).

The w124 and w201 use the same DS flanges. The small, medium and large flanges are dictated by engine torque.

The brake/clutch assembly has a couple of switched built into it for criuse control deactivation. Don't remember the details, it's been 5 years now.

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The reverse light switch is on the shifter. The harness from the auto shifter should plug right in. Not positive for your application, but this is the case for later cars.

For the CC, the clutch switch needs to go in series with the brake light switch.

What kinda quotes were you getting for a custom drive shaft and in what material?

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#dontdealwithkahlil

Okay, figured out some things:

Turns out, a reverse switch came with the 5 speed conversion stuff I bought -- it was hidden inside a little baggie. Even more fortuitously, the person who removed the stuff from a junked '87 190 2.6 included a length of the two wires that plug into the switch. One of the wires is grey and yellow and the other is black and yellow.

Underneath the car, the neutral safety switch has four wires going to it. One of the wires is grey/yellow and the other is black/red. I'm thinking I can tie grey/yellow to grey/yellow and black/yellow to black/red. I see where the connections are under the dash, but I think it would be easier to route the wires from the console to the NSS via a small hole drilled into the trans tunnel. I would snip off the end of the NSS to make the connection complete.

The other two wires in the NSS are the purple neutral safety wires. I think I can connect them without issue. I wouldn't have the neutral safety feature, but I can live with that.

Let me know if there's something I'm missing. I still need to figure out what's needed to make depressing the clutch shut off the cruise control.

The price I was quoted by a local race shop for a steel one-piece driveshaft is $2-300. The proprietor offhandedly remarked that a carbon fiber driveshaft would be about $1,000 more

Corvo Gold

The MB engineers already thought of all this, remember that a high percentage of 124s were factory equipped with manual transmissions.

There is a 4 pole connector X49/2 for the auto transmission NSS harness located under the carpet on the drivers side of the transmission tunnel.

There are 4 wires
1: Black/red - power from Fuse 7
2: Gray/yellow - to reverse lamps and the rear window wiper control relay
3: Violet - start signal from key
4: Violet/white - to starter solenoid

From X49/2 the wire disappears through a grommet down underneath the car where it plugs into the NSS.

The auto transmission NSS closes a contact between pins 1 and 2 in reverse, and another contact between pins 3 and 4 in park or neutral.

The manual cars came with a plug on the other end of the shifter switch harness, that put the reverse switch contacts between pins 1 and 2, and then jumped pins 3 and 4 since there is no starter interlock on a MT car.

I would pull the NSS harness off the auto transmission back up through the grommet hole in the tunnel. Then I would modify the harness as follows:
- clip off the plug going to the transmission.
- Separate the wires.
- Join the violet and violet/white wires close to the interior connector.
- splice the black/red and gray/yellow wires to your shifter switch connector.
- seal the grommet hole in the tunnel

For the clutch pedal switch, I would dig around under the dash for a 2 pin connector that would be taped back to the harness and would have a jumper plug stuck in it. If the wires are black/red/white and black/white then that may well be your clutch switch connector. The black/red/white should ring back to the brake pedal switch and the black/white should ring back to pin 8 on the cruise control amp connector.

If you can’t find this connector, then you’ll have to do some modifications. On the brake pedal switch there is a single black/red/violet (power from fuse 5) and on the other contact there are multiple black/red/white wires. You’re going to have to unsolder these wires from the brake pedal connector and then figure out which of these wires is going to pin 8 of the cruise control amplifier connector. The wires that did not ring out to the cruise amp get soldered back onto the brake pedal connector (they go to your tail lights and the alarm system).

You will need to wire your clutch switch between the brake pedal connector and the wire you rang out to the cruise amplifier. If your switch does not have a connector, visit the dealer and get the proper connector. Solder two wires to this connector.

One wire will go to the brake pedal switch where you removed the black/red/white wire from. The other wire will be attached to the freed black/red/white wire going to the cruise amp.

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The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech

Jay_Bob,

Thanks for the great information and fine ideas -- I need things explained to me precisely since my automotive ambition often outstrips my mechanical instincts. I will investigate after work today if I haven't collapsed from exhaustion.

Part of my confusion is that I don't have the full reverse switch harness (it came to me cut off), and, as it turns out, no clutch switch is attached to my MT pedal box.

Again, many thanks.

Corvo Gold

I don't see how Flex discs are going to work with a single piece driveshaft because the front and rear DS halves are at slightly different angles with a U joint in the middle. Are you going to convert to U joints at both ends? Also the flex disks help protect the 5spd from shock loads. Mercedes never offered a 5spd manual om603 turbo from the factory anywhere in the world. This 5spd is not designed for the torque of the om603t. I think a single piece DS will shorten the transmission's life.

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Corvo Gold, do you still have this wagon? I currently own a 5 speed swapped 87 300TD. I am wondering if i got your car? lol