96 E300D Transmission
 

Hi,
Just finished fixing up a 96 E300D that i bought. The transmission shifts just fine when driving normal, but when i rev the car up to 5000 rpm it shifts rough into the next gear. It does shift smooth when the car revs up to 4000 rpm. The only time is shifted hard was when i red-lined it. I know that the any car shifts hard when red-lined but it seemed a bit too rough.

Also, if worst case, how much for a rebuild?

My transmission behaves in a similar way and I believe it's designed that way. The harder and quicker shifts protect the transmission at higher speeds and loads. I find that if I ease on the throttle before the transmission upshifts at high RPM's, it's a lot smoother. Keep in mind this was the last year of the vacuum-control transmissions which by today's standards are quite primitive. The newer, electronically-controlled transmissions are more intelligent and can shift smoothly and consistently in any situation.

I wouldn't worry about a rebuild, but I would drain the transmission pan and torque converter, replace the filter and refill with a synthetic ATF if that hasn't been done lately.

Check the fluid level as well. A low level will cause abrupt very hard shifts.

I would say don't redline it and enjoy your properly operating transmission, but I am somewhat of a simpleton........
The fluid/filter change never hurts.

Here's another thought: try adjusting the transmission's vacuum modulator. It's on the driver side of the transmission pan. On the older models like my '82 300D the modulator made a big difference in shifting speed and smoothness. On my current '96 it seems to make no noticeable difference in normal driving but I do feel some improvement on those high-RPM, full-throttle shifts. Give it a try. Turn CCW to make the shifts smoother.