Automatic gear box jumping out of gear?

[Chris Atherton]

Hi, I have a 2005 w211 e320 cdi Avant-garde with an auto box, and on 2 or 3 occasions I have been driving at about 50 or 60mph when I have lost drive, and the engine has gone to maximum revs, and I have started to slow down on the motorway (quite frightening). I tried taking my foot of the accelerator, but when I put it back there was still no drive, as if it was in neutral, or perhaps in first gear, which was having no effect because of the speed I was going. Each time it has happened I have come to a stop, but then the car is alright again when I drive off. Has this happened to anyone else? There are several other things wrong with the car as well, and if this is a serious fault I may have to scrap it!

 

[Larkone]

Is it low on ATF?

 

[brandwooddixon]

It could be a number of things, but unless someone has experience of exactly the same problem I would think that getting codes read would be the first step.
I would suspect the gearbox electroplate. They tend to be susceptible to oil contamination.
Depending on the vehicle any replacement may need to be coded to the car, in which case you will need an MB specialist.
You mention other issues are present with the car, I think that a trip to a specialist to get codes read and the ATF checked would be the first port of call.
Anything else would be guesswork.

 

[LostKiwi]

It could be a number of things, but unless someone has experience of exactly the same problem I would think that getting codes read would be the first step.
I would suspect the gearbox electroplate. They tend to be susceptible to oil contamination.
Depending on the vehicle any replacement may need to be coded to the car, in which case you will need an MB specialist.
You mention other issues are present with the car, I think that a trip to a specialist to get codes read and the ATF checked would be the first port of call.
Anything else would be guesswork.

This all day long.

 

[rifiki]

Sounds like electroplate, had similar problem years ago.
Before you start throwing £££ at it get the code read using MB STAR diagnostics.

 

[MinionBob]

Check the fluid level first. a cheap DIY job at £10 for a dipstick. Needs to be done warm, and that is a good 20 mins driving...

 

[ajlsl600]

This all day long.

Part integral to gearbox durr! Normally designed?? To be full of f oil, suseptable to oil contamination. Wot a f shock. I sure wud not want a trip off planet in f all made by benz and prob any other car maker!!

 

[rich.g.williams]

Hi, I have a 2005 w211 e320 cdi Avant-garde with an auto box, and on 2 or 3 occasions I have been driving at about 50 or 60mph when I have lost drive, and the engine has gone to maximum revs, and I have started to slow down on the motorway (quite frightening). I tried taking my foot of the accelerator, but when I put it back there was still no drive, as if it was in neutral, or perhaps in first gear, which was having no effect because of the speed I was going. Each time it has happened I have come to a stop, but then the car is alright again when I drive off. Has this happened to anyone else? There are several other things wrong with the car as well, and if this is a serious fault I may have to scrap it!

Yes the mechanism for this to happen is for the modulation pressure solenoid to turn full on bringing modulating pressure (and hence working pressure in the transmission) right down, as soon as working pressure is too low the hydraulic state of the gearbox can become indeterminate and drift into a pseudo neutral (selector lever is still in Drive). Shift pressure may also be implicated.

Strategy is first to search for any stored ETC (TCU) codes and there should be some, they may explain what happened.

Blaming the conductor plate or ATF seepage or ATF level up front is over simplistic (shame) it could be a solenoid or symptomatic of other problems.

Next strategy is to open the sump and look at the oil quality and look for any metal particles in the sump and around the magnet, some iron filings around the magnet is ok, heavy chunks on the magnet or spread around is not.

If the ATF is especially mucky its worth servicing the valve body, cleaning the solenoids and conductor plate, replacing the filter, refilling with new ATF and see if problem persists. If it does then maybe swopping the conductor plate is a good idea.

Given this situation be aware that the hazard here is the small possibility that the transmission could shift randomly down to a low gear and likely lock the back wheels so best to discontinue regular use of the car until the issue is completely resolved.