Gearbox starting to die ?
 

Hi
Today while I was driving at around 60KPH my C320 2002 suddenly did a shock movement as if it hit a wall for two seconds, I kept monitoring the car and I noticed that this was happening at lower speeds when the gearbox changes gears, so I did switch to tiptronic since I thought maybe the car computer is not switching gears properly, while in tiptronic and without switching gears the RPM suddenly jumped up to around 7. So I switched back to regular automatic gear, after that I noticed two issues.

1- The car would not switch back to tiptronic no matter how much I tried, I.e. the LCD display always showed D
2- While in a traffic jam, and while switching from N to D, each time I would switch to D the car would jump forward "sorry for the expression English is not my native language, the car felt as if it was hit from behind each time I switched from D to N" this happened without any abnormalities in RPM ?

During all of this the computer board did not signal any problems.

So when I got home I turned of the car, after a few seconds I turned it on again and moving from N to D was as smooth as ever and tiptronic worked again.

OK I hope I did explain it in a humanly understandable way :). So what is going on ? Gearbox tear and wear ? Gearbox Oil ? Gearbox seats ?

Any hints ?

Thanks

very very common problem, youll need whats called a conductor plate..which is on top of the valve body, there will probably be a code for turbine speed sensor stored in the trans control unit. or you could need a shifter assembly. those are the most common problems.
ofcourse there could be something other than those 2 items like the valve body, but unlikely. also sometimes the trans control unit can get transmission fluid that leaks up into the control unit via the wire harness which can have similar symptoms as you describe.

Hi
Thank you for the clarifications, today while driving to work the same issues happened and I got a Check Engine light. I did pass by a small shop who did use a generic scanner and got me the following codes :

the transmission has an impermissible transmission ratio
The gear comparison is negative or the target gear is not reached

Does this change your initial assessment ?

Thanks a lot !!

I assume this is the conductor plate

http://www.carsteering.com/data/all_...1402701161.jpg

How can I get to it ? I will have a shop do it, but I would like to know the inside/outs so that I dont get ripped off.

yes that is a correct picture of it. at a benz dealer we charge about 2-3 hours labor plus about 4 quarts of tranny fluid. part is about 200-300 bucks maybe cheaper. they will need to drop the pan and remove the valve body, and shift valves, they will need a "tool" to measure the trans fluid level. yes those codes are equivalent to the speed sensor codes. that should cure your issue. make sure they know what they are doing and have the proper tranny fluid level when done. good luck.

Thanks for the insightful response, so the speed sensor is basically a part of the conductor board. What is the correct fluid level after they finish ?

yes the speed sensor is the round platic/metal top thing at the middleish of the board. normally 4 quarts will bring it close to the correct level. but you should make sure with the proper dipstick tool. which if you mechanic works on Benzes, might already have to tool.