Mercedes Repair Questions? Ask a Mechanic for Answers ASAP
Hi Stephen - harsh gearshifts can be a fairly long drawn out diagnosis process on these vehicles. We deal with numerous cases and the problem can be down to many different things which can all cause very similar symptoms. An experienced transmission specialist should be looking at this with specific knowledge of Mercedes 7G transmission. I will outline the steps that should be taken & the possible causes below:
The first step which has been taken by your dealer is a check for transmission software updates - but also ensure that the engine software has been checked & updated as well if required as these 2 systems talk to each other and if just the transmission software has been updated then this can cause conflicts
Next is to check the adaptation data - this is the self learning information inside the transmission. The data should be checked for all gearshifts to ensure it is within specification. If out of specification then this would usually indicate a mechanical problem inside the gearbox. All shifts should be checked as data from a higher shift can affect a lower physical shift point.
If all of the data is within spec then the problem gearshift will need to be readapted - this requires road testing the vehicle with Mercedes STAR diagnostic tool to relearn the shift data - it can take over 10 learning processes to fully adapt a shift!
Also with a shift problem in first the torque converter should also be readapted as it can often be the lockup clutch causing problems rather than an actual gear shift (which can feel the same when the clutch cuts in or out)
The oil level should also be checked and at this point if the shift is still not improved then the gearbox sump would be removed & checked for any signs of excess swarf to indicate internal wear. A transmission flush is also a good idea at this point
The gearshifts should again be readapted at this point
Build up of debris in the valves on top of the valve body can also be a problem & the valve body may need to be removed to inspect & clean these
If after all of this there is still a problem then the factory will need to inspect the data from the transmission - they can tell at the factory if the problem is a hydraulic fault (generally requiring a valve body replacement) or a mechanical fault (requiring a gearbox strip down and overhaul)
We have seen all of the above causing the exact same symptoms so it is important to follow a good diagnostic path for transmission faults of this nature
Let me know if you need any other help - I understand the information is quite lengthy but in reality this is an accurate overview of the steps required with your symptoms
Best regards, Paul
I have read on the forums that this is a common problem and that it is part of the design
Is this trus
Is this true
It is a fairly common problem, but is usually down to a fault if it is this noticable - early software versions used to be a real problem but if it is still doing it after the latest software (and the gearshift data has been successfully readapted!) then there is usually a fault as described above if the shift really is that harsh
Readapting the shift data can be a real pain - I have literally spent hours trying to readapt the gearshifts with STAR attached!