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MB Paul
MB Paul, Mercedes Technician
Category: Mercedes
Satisfied Customers: 4317
Experience:  Mercedes Benz Qualified Diagnostic Technician
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I have a mercedes ML320 CDI 2006 on a 56 pl;ate When I am

Resolved Question:

I have a mercedes ML320 CDI 2006 on a 56 pl;ate
When I am driving and I come to a slow stop, the gearbox jerks into first gear.
This does not happen every time under the same circumstances but happens 60 to 70% of the time.
The jerk is quite noticeable and occupants of the car feel it clearly
All other changes are smooth and it never gets stuck

Mercedes have checked the software and they say it is up to date

Can you help

Stephen
Submitted: 3 years ago.
Category: Mercedes
Expert:  MB Paul replied 3 years ago.

MBpaul :

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:

MBpaul :

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

MBpaul :

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.

MBpaul :

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!

MBpaul :

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)

MBpaul :

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

MBpaul :

The gearshifts should again be readapted at this point

MBpaul :

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

MBpaul :

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)

MBpaul :

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

MBpaul :

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

MBpaul :

Best regards, Paul

Customer:

I have read on the forums that this is a common problem and that it is part of the design

Customer:

Is this trus

Customer:

Is this true

MBpaul :

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

MBpaul :

Readapting the shift data can be a real pain - I have literally spent hours trying to readapt the gearshifts with STAR attached!

MB Paul, Mercedes Technician
Category: Mercedes
Satisfied Customers: 4317
Experience: Mercedes Benz Qualified Diagnostic Technician
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