I have "almost" everything you'd need to convert to a 5-speed setup sitting in my garage right now, including a recently rebuilt tranny. If you were converting a W201 (190 series car) to a 5-speed, I would have 100% of everything you'd need.

5-speed 190's are not too difficult to come by. 5-speed W124's (your 300D) are much more rare.

Working from memory, the only differences between installing a 5-speed in a W201 and a W124 will be:

1: Front driveshaft - you'll need a W124 5-speed front driveshaft, or a modified automatic shaft. You may need a new front flex disk, depending on which shaft you end up using.

2. Tranny crossmember - the W201 and W124 use different crossmembers. You may be able to modify an automatic crossmember (not sure, but it's possible on a W201)

3. Shifter rods - I'm not sure if the rods are the same length between a W201 and W124.

The items which are the same are as follows:

Tranny, flywheel, clutch, pressure plate, pilot bearing, throwout bearing, pedal cluster, shifter, master cylinder, slave cylinder.

You can typically buy a complete setup for a W201 for under $1000, then your additional costs would be the front driveshaft and possibly the shifter rods and a flex disk.

I hope this may be of some help.

SteveM.

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'93 190E/D 2.5 Turbodiesel 5-speed (daily driver)
'87 190D 2.5 Turbo rustbucket - parts car
'84 Dodge Rampage diesel - Land Speed Record Holder
'13 Ram 2500 Diesel
'05 Toyota 4Runner