1993 w140 300sd transmission sluggish forward and reverse. What to look for?
 

I will start by saying the wiring harness and vacuum system are both in horrible shape.



I have no idea what controls this transmission but I'm pretty sure the W123 and W124 would still drive fine without any electronics or vacuum just with very harsh shifts.



This thing requires a lot of throttle to get it to move in either direction.



Where should I be looking?

Hard to say without driving it. The w140 is a big, heavy car, so it could be nothing. My 1991 350sd and my 1993 300sd, both with the OM603.97 rod bender engine drive quite different. The 600lbs in the w140 makes a difference, even for the 3.5L 603.

A lot of throttle doesn’t mean much, and again could be normal.

First and foremost I’d want to know if I’m getting boost. Do you know how to pull codes on this car? Go on eBay and buy a $38 code reader led box… understand the edc codes especially. The. Start figuring out about boost. Have any? Enough? Ideally install a boost gauge via the nipple on the manifold and a three way rubber fitting. There’s a good chance thst the vacuum operated wastegate is affecting boost and thus slowing things down…

How are the fuel filters? Once driving at speed on the highway, will it do 80MPH with ease on flat land? Any smoke?

There seems to be a transmission issue of some sort. It takes around 3k+ RPMs to get it to budge forward or backward and it's just crawling at that.

The engine seems to run fine, but with how it is now, there's no way it will go on the road at all. I would guess 10mph would be top speed and I'd guess it would be damaging the transmission and redlining it to get that 10mph.

Yeah that isn’t right. I’d avoid driving it until you have it figured out.

I would want to re check fluids, and it’s probably worth a pan drop to see what is in there. Possibly a clogged filter, or filter that the media has failed. Beyond that it could be the pump, torque converter, clutch packs, etc.

Are you sure it isn’t stuck in some higher gear and the TC is just shearing the fluid like crazy?

Turns out it was low on fluid. I had checked it when the car was purchased (was a non runner) and I thought it looked ok. It barely drove off the trailer when I was able to get it started. Checked it first thing in the morning and it wasn't registering on the dipstick. Put about 20oz of fluid in there and it now drives as it should. Why it was low will be the question but hopefully it's a slow leak.