Is it possible (realistically speaking) to replace a 4speed auto in a 92 400e with something like a 5spd auto from an S420?

Along with the rear diff swap, this would seem to be a logical way to increase low speed acceleration along with keeping freeway revs down.

Let's assume for a moment a whole donor car could be sourced for all of the needed parts or is there something totally obvious that I am missing?

At this point, this is more idle curiosity than anything else.

Thanks,
Jim

There was a company that made first gear start kits for MB V8s but they're out of business. Maybe someone has a kit to spare.

Sixto
93 300SD

Not feasible, at least in the example - the only way to get a 5 speed from a S420 is a 96+ 722.6 which is a fully electronic transmission.

the 400e is already set for first gear start unlike the 500e and the 300e. That will not make a difference.

Hi again,

The first gear isn't the issue - mine starts in first - with the other diff the overall gearing will be much lower, giving better ingear acceleration all across the board, however freeway cruising will be at much higher rpm than stock in top gear - 4th. Going to a 5th gear would get it back to where it would be comfortable.

Please forgive my ignorance - what is it with a "fully electronic" transmission that makes it impossible to work with the older W124?

Thanks,
Jim

What would you plug it in to? It's part of a broader electronic system including diagnostics that your car does not have.