Sometimes you just have to laugh.

A friend of mine with a 1990 560SEL calls me up about a month ago. He says their 110K mile creampuff 560 suddenly lost power, started shaking, and barely made it home from the corner store. I tell him to start with a tune- up as it sounds like maybe it flooded and only runs on a few cylinders.

Fast forward to yesterday- Still same issue, so I tell him to go ahead and tow it up.

Winds up that the engine sounds and seems to run fine, BUT runs like "Whup- Whup- Whup" as the car tries to hop like a Southern California funny car. Further checking shows that reverse works fine, but Neutral wants do do a hopping, lunging reverse, and the forward gears act like there's no trans fluid in the trans, and the car hops forward slowly like it's got a badly bent propeller shaft. In Park, it hops backwards until the parking pawl kicks in, then it does the Jumping Bean trick.

While checking basic settings, I notice that the RPMs aren't changing hardly at all- it REALLY feels like the trans is being quickly and rhythmically shifted between "park" and "reverse".

No vacuum leaks. Brakes are free. Trans fluid level is correct. No leaks. Trans fluid is clean. Drive shaft, rubber discs, joints, and bearings are all good. Propeller shaft and drive axles are dead straight. Shift linkage is adjusted perfectly and bushings are good. The neutral safety/ reverse lamp switch is functional.

It acts like the trans is stuck in reverse... all the time. In Drive, it's a two steps forward, one step back experience. Amazing.

So...

1) Transmission internals are one thing I'm not trained in. And, of course, I have three factory volumes on this chassis and this engine. Guess what they don't cover? Nice.

2) Transmission experts: Is this some common stupid thing that can be fixed? Crap in the valve body? My gut tells me that it's time for a transmission and torque converter transplant. Problem is, you can buy another 560 for less than the cost of doing it right and the shipping on the trans, converter, and cores.

3) I have a buddy with a pretty much junk 1984 380SE. The trans on this car is about the ONLY thing good. Can this be installed in the 560? What are the fitment issues, and what are the downsides to doing this? I know they're two different transmission numbers, but they're the same family.

Ideas? Thanks in advance.

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1968 230S Automatic, Elfenbein
1975 O309D Executive Westfalia Camper Bus, Blau/ Weiss
1972 280SEL 4,5 Dunkelrot
1966 VW Type 34 "Grosser" Karmann-Ghia
1963 VW 1500 Variant Pearlweiss
1969 VW Variant Automatic, Perugruen
1971 VW Squareback Automatic, Clementine Orange
2001 E320 4Matic Wagon- Our belated welcome to the 21st century! Polar White
1973 280SEL 4,5 Sliding Roof "The Bomb", Dunkelblau.