4th gear is 1:1 in the W201 automatics. That's a fact. The only "overdrive" transmissions available in W201 cars are the non-Getrag 5 speeds. The Getrag 5-speeds in the 16V cars use a 1:1 5th gear.

To be sure about the rearend, check the numbers stamped into the rearend housing (assuming the gears have not been changed internally). You can find these numbers stamped in one of the "ears" located at the lower left hand and lower right hand corners of the rearend housing.

Then do the math to figure out the rpm's based on the rearend ratio and tire diameter.

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