MBWorld.org Forums - 1999 E320 Automatic Transmission... is it F*ed Up Forever?

Hey Everyone! Thanks for all of the posts you've previously left here. I've read through them and learned a lot, but I still have some questions and I'm hoping I can borrow some of your expertise as well!

This is a story of neglect, unfortunately... I'm hoping I'm not too late. I'm helping a friend with an 1999 E320 4matic (I believe it is the W210). She had what seemed to be a total transmission failure while driving about a week ago. The car has been parked since then. After the incident that left her stranded, she told me that the transmission had been shifting sluggishly for the past couple of weeks, but she thought maybe it was just the car reacting to colder weather. :scared: The car is new to her within the last month or so, so the neglect goes far beyond this time period, I'm afraid. Unfortunately, the transmission failure scared her when she was on a busy highway- she couldn't get above 2nd gear- and tried to compensate by giving more throttle. She drove it long enough to get it off the road and into a parking lot at very high RPMs... approximately 3-4 miles of redlining the RPMs. Interestingly, there was never a check engine light nor any external indication of limp home mode-- just a failure to shift. She also mentioned that she may have noticed some smoking coming from the car previously/intermittently, but couldn't be sure if it was coming from her car or other cars around her. Given what I found (see below) I think it is probably safe to assume that the car has probably been smoking.

Today I checked it out for her. I put my OBDII tool on and there were no permanent fault codes, but a pending PO700 code for Transmission Control System Error. I lifted the motor cover and checked tranny fluid with the MB dipstick. At cold temp, there was some fluid on the dipstick, but upon running at temp, it was low-- in fact, about 5 quarts low. It is untelling how long it had been without appropriate the fluid level, but the last transmission fluid change was approximately 80,000 miles ago, and it probably hasn't been checked in at least a couple of years. I added some Lucas transmission fix in addition to the 5 quarts of fluid. Here's what happened:

-The car smoked. A lot. It was definitely a grey-ish smoke that you might expect to see with transmission fluid, but it seemed to be much more than I would expect for spillage, although I know some fluid did run off the side of my funnel-- maybe more than I realized, but it still seemed like an awful lot of smoke. When looking underneath, it seemed that the smoke may have been coming from the exhaust-- then again, it is very near the transmission pan and some smoke did appear to be coming out of the transmission access port (where you insert the dipstick), so I'm not entirely sure if the smoke was coming from the top of the exhaust (like from spillage) or if it was coming from inside the transmission and exiting near the exhaust. Again, she said that it may have been smoking intermittently over the last couple of weeks. Is it possible that the transmission is running way too hot? Is there any way that this smoke could be originating from inside the transmission? The car did not overheat and there doesn't seem to be any problem with the radiator. I then took it for a test drive.

-After adding the fluid, the car appeared to shift up the gears fine (contrary to what happened to her on the day that it failed). However, the downshifting was not as smooth-- particularly from 2nd to 1st when applying the brake. I read the forum about this issue which suggested cleaning the MAF sensor-- this is definitely doable, and makes sense even given the amount of smoke that the car produced today... if this has been consistent, the poor MAF sensor may be a wreck. I did notice that the air filter was in pretty good shape though. The car continued to smoke throughout the test drive. Temperature gauge continued to read normally.

-When I parked the car, I checked the transmission fluid again while running. It continued to smoke (this was after a 10 minute drive and 10 minutes or so of idling, so again, not sure if spillage would continue to produce this much smoke for this long). Transmission fluid was now at an appropriate level, but the color was horrible. Like motor oil blackish brown. I did not see any visible puddle of transmission fluid under the car.

I'm trying to figure out next steps. I'm thinking of draining the transmission fluid and replacing with fresh. Then, after a short while (maybe 100 miles?) draining again but this time replacing transmission fluid, filter, and pan gasket. I can also clean the MAF sensor during this time to see if that alleviates the harsh downshift issue. Any thoughts on this plan? Anything I should be aware of? Also, given the location of the smoke, I wonder if there may be a leak from the 13-pin connector plug O ring that seems to be a notorious issue? Should I replace that as well? Last question-- should I be on the lookout for any other problems, including potential vacuum modulator issues? I am not familiar with these, but I understand that for cars that have them, they can definitely create a smoke situation, so I want to be aware of any alternative hypothesis that you all might have before I endeavor into the "wrong" fix and tackle a problem that isn't the right one!! I'm also hoping I can help her get this issue corrected before any more damage is done. Hopefully it isn't too late already. Thanks SO MUCH for your advice!