I am totally new to this forum, except that I have read and been helped by several posts in the past relating to my 2005 E500.

A few months ago the transmission started hesitating when first put into gear. This went on as a minor irritation, but eventually left me stranded in a parking deck. Had the car towed to my mechanic, who kept it for two weeks, only to tell me he could find nothing wrong with it- it went into gear perfectly and drove fine. Hmm...how could that be? I took my son with me to pick up the car, and when I got in to drive it home, it would shift easily into gear, but the transmission would not engage exactly as before. Then a thought occurred to me: which of the two keys had I been using, and which had I left with the mechanic? Since I had both keys with me, I switched keys and Voi Loi! it shifted into gear perfectly! The problems was apparently within the electronic key. The 'faulty' key has never worked since, even with battery replacement.
Now fast forward 6 months. Started noticing hesitation in the transmission when first shifting out of park a few weeks ago. Now my one good key (even with new batteries last month) has done the same thing, leaving me stranded (at home thankfully) once more.
I've tried resetting the transmission per instructions involving the accelerator, which I either didn't follow correctly or had no bearing on my problem (which I cannot test since the car will not move).
Does anyone have suggestions on resetting the key or is there something else that can be done?

 

Well, I had the car towed into my local MB dealer. They pulled the trans pan and then informed me that I needed a whole new transmission. When I asked them specifically what was wrong with it, they said 'we won't know unless we tear it apart', and the only physical evidence was that the oil was 'dark as motor oil'. I had them put the car back together, and had it towed to my local non-MB specific mechanic that I've used for years.

Doing more research, it looks like others have experienced similar problems which turned out to be the Transmission Valve Body. Thoughts?

 

Dark transmission fluid is never a good thing.


You can change it then run it a little bit and send a sample to be analyzed and that might point in the right direction.
It is either really burnt (slipping clutches) when could be a valve problem, but may be too late to fix.
OR it is a lot of clutch material, meaning there is probably little left on the clutch that failed. (Maybe caused by a valve problem).


Never drive a car with a transmission not feeling quite right. It only adds to whatever damage is happening.

 

Agree; yucky fluid is no good and leads to a variety of symptoms.
Agree; easy and cheap to change it and see if it helps. It just might!
Sounding proverbial here; "Never pay the big bucks for a new tranny until you spend the little ones to see if that does the trick!"

I think HVAC guys (home and auto) have the same knee jerk reaction as the "won't know the problem until I rebuild your transmission" guys. In AC, it sounds like this: "I don't know what's wrong with it. Must be the compressor!" Just like the transmission, they want to replace the most expensive part first because they don't know any better way to troubleshoot the problem.

I have a '97 Ram truck. Once I took it to the shop because the AC went out. They kept it for a day and then told me the 'compressor' line. I was young and naive, so I said okay, but also requested that they see if they could fix the horn that was also on the blink. They said they would take a quick look at that before I left the dealership. In 10 min they came back and said the horn fuse was blown and that (since they are on the same circuit) when they replaced the fuse, the AC started working again! Remarkable! They were willing to replace the compressor, but the problem was a $0.10 and serviceable part! Jeeesh!!!

At risk of offending purists, my advice would be to buy a manual oil extractor ($70) and $125 worth of Shell equivalent ATF. After three pump-out and refills, you'll have changed almost 90% of the fluid and have an indication about the problem for <$200 and you'll never have to get dirty or under the car to do it. (I have the bad radiator in my '03 E500 and do this to my 5 sp tranny once a year. I could do this twice a year for 10 years and still not be up to transmission replacement funding levels!)

 

Dirty (dark) transmission fluid can damage your transmission but it doesn't necessarily mean the transmission is toast. Burnt fluid which can be a dark reddish brown has a very distinctive (stinky too) smell to it. If your mechanic smells it he will know. If the fluid is burnt, your transmission is beyond hope and it needs to be rebuilt/replaced, changing the fluid will help no one but the store that sells it ti you. If your fluid is just dirty but not burnt, drop the pan, clean it and do a tranny flush/service and get that sucker going again. Hope a burnt tranny is not the case, and I am glad to see that you hauled it out of the dealership, they more than likely would try to sell you a new tranny even if its just a bad solenoid, sad but true.

Good luck and keep us posted!

 

Burnt fluid does not mean the trans is toast any more than (and probabaly less than) otherwise discolored fluid.


The issue is finding the cause.


Clutches can get hot enough to burn fluid without losing too much material.
On the other hand if they have disintegrated into the fluid, even with enough cooling to dissipate the heat, that particular clutch is toast. (and no one does one clutch, so it is a full rebuild.)

 

Not sure I understand your post. A bad transmission does not mean every single component is bad... clutch discs are metal discs covered in a material that will in time wear out, specially if overheated but the disc does not disintegrate.
When it comes to clutch discs, the packs can contain good and bad discs, but one would have to be dumb to tear an auto transmission to replace a couple of discs so your analogy makes no sense. At the end even if only half of the discs are bad, any transmission guy will agree that the tranny is toast and needs to be rebuilt, not a lot of options there, saying otherwise will be misleading information that will give the OP false hope.
There is a HUGE difference between discolored fluid and burn fluid. Burnt fluid has lost most (if not all) of it's needed properties, and at that point the transmission has operated on burnt fluid damaging more than just the discs (Pump, seals, etc,etc) Also, if it is is burnt, the chances of discs being good or usable are slim to none. If you think you can replace burnt fluid from a transmission and keep it running for any period of time you are daydreaming.

 

You can certainly overheat the fluid and get it to the point where it is discolored and has the very noticeable "burnt" odor without doing permanent damage to the transmission.

Yes, continuing to run that fluid will most likely result in damage.

On the other hand, a transmission valve or sensor failure can cause excessive wear on one or more clutches, darkening the fluid (without the burnt smell).

In the first case fresh fluid is all you need (provided the conditions that overheated the fluid don't continue to occur)

In the second case you probably need a rebuild in the very near future.

In this case it seems he noticed a problem and then continued to drive for months, so I would guess that whatever the original issue was, his transmission now has multiple problems.

Looks like a used trans is about $2,500 plus whatever a good Indy shop charges for an R&R, filter/fluid change and whatever MB specific programming is required. (I have heard there are dealer only settings, but that is second hand)

 

Hey guys I have a 1999 S420 that's been running fine and all of a sudden I drove her today and I heard a slight grinding noise so I parked then came back and now she won't engage any gear at all.

 

Goingback2Cali you should post on the W140 forum for the '99 S420