1997 E420 Transmission Shift Quality Deterioration
 

1997 E420, 56K miles, manufactured 3rd quarter 1996. Equipped with 722.6 electronic transmission - fluid and filter renewed 18 months ago at 50K miles, using M-B parts.

Over past couple of weeks, the transmission's shift quality has started to deteriorate.... to the point that the 2-3 and 3-4 shifts are now rather drawn out and accompanied by an almost head-jerking completion of the shift. Shift quality can be tempered somewhat by modulation of the accelerator pedal.

Prior to this, shifting has been asymptomatic and the transmission has required no service since new, other than fluid renewal.

Quick inspection reveals proper fluid level, with no evidence of leaks.

Any ideas? Control unit failing? Or is this one of the early 722.6s that will require an overhaul?

Were there software upgrades required for these early W210 electronic transmissions?

Without a way to monitor the transmission oil temp, there is no real accurate way to measure the fluid level. However, without a leak, one would wonder why the fluid level would change. In addition, MB seems to actually more concerned about overfilling than underfilling, as the case is scavanged of oil to increase efficiency. But it is important to be certain the oil level is correct. You should also examine the color of the fluid to make sure it isn't cloudy looking, as a bad trans oil cooler will cause coolant to get into the ATF, which can lead to this problem (harsh shifting).
I would also ask if the correct ATF was used, the special trans oil MB sells specifically for the 722.6.
Gilly