450 SL transmission problem
 

I recently purchase a 1977 450SL with 170,000 well maintained miles. On my way home with the car from Kansas City to Arkansas, I noticed that the car stopped upshifting from 1-2. It will shift by letting off the accelerator. Also, on the 2-1 down thift there is an audible thump in the transmission. It goes into reverse fine though. The transmission fluid is brown so I ordered a gasket and filter set and plan to change and see if that helps, I've also read that the B-2 piston on these models is a problem. Any suggestions?

thanks.

450 SL tranny
 

I'd say your starting on the right track by changing the fluid. That could make a big difference. Be sure they (you) change the torgue converter fluid too. I believe the B2 piston affects reverse first. Not sure, anyone? It's referred to as catastrophic transmission failure. That's enough to scare the **** out of ya.
sbr
'79 450SL
milanbraun/palomino
76,000mi.

Brown fluid - very bad sign. Depending on how often the fluid was changed you could cause the tranny to fail by changing the fluid. I have it from several dependable sources that if the tranny has not had regular fluid changes, when you put fresh fluid in, they often fail within a few months of the change.

The B2 piston is not used for reverse at all.

Its my guess that you are in for a rebuild soon.