Thump when shifting transmission into gear
02-26-2023, 11:01 PM
#1
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Thump when shifting transmission into gear
I've noticed a slight thump when I switch into drive or reverse sometimes. Especially noticeable at first start when car hasn't been driven for a while. I changed the transmission mount hoping it would help but it's still the same. Any ideas what it could be? Car has 46k miles on it.
02-27-2023, 01:18 AM
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Last 5 years: S560, X7, X5, Accord; Sold:15'S550, 20'BMW X7; 19'BMW 530e; 20'Lincoln Navigator,LS460
I've noticed a slight thump when I switch into drive or reverse sometimes. Especially noticeable at first start when car hasn't been driven for a while. I changed the transmission mount hoping it would help but it's still the same. Any ideas what it could be? Car has 46k miles on it.
02-27-2023, 08:47 AM
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1984 W126 300SD & 2013 W221 S550
W221s display the same issues as they have the same transmission, less two extra gears, but all are shifted by the same mechanism: the Intelligent Servo Motor (ISM). The ISM is responsible for shifting into gears and emergency operations such as forcing the car into park, if the driver's door is opened in gear and rolling is detected. With that being said, the internals of the 9G Tronic (W221s are the 7G Tronic) are the same to ~70% of transmission on the market and use the same principle for locking the transmission and driveline while in park. This method uses a parking pawl that engages on a thick toothed gear present on the output shaft to prevent rotation. Thus if the vehicle is resting even at a slight angle significant forces are present on the parking pawl and gear. To prevent this and by proxy extend the life of your ISM (even on the slightest angled surfaces): hold the brake pedal, set the parking brake, then engage the transmission into park. 90% of this thump will go away as the forces are present on the rear parking brake not the parking pawl.
However, if this thump is present on very level surfaces, your ISM and/or Transmission Mechatronics needs to be synchronized or calibrated! I forgot what it is officially called, as I haven't performed the procedure in years, but it is a very simple process with a Xentry system. I will see if my Mercedes Work Shop Information System has any documentation for the procedure.
However, if this thump is present on very level surfaces, your ISM and/or Transmission Mechatronics needs to be synchronized or calibrated! I forgot what it is officially called, as I haven't performed the procedure in years, but it is a very simple process with a Xentry system. I will see if my Mercedes Work Shop Information System has any documentation for the procedure.
The following 2 users liked this post by w126w221:
as.thompson (02-27-2023),
Sactownmb (02-27-2023)
02-27-2023, 01:41 PM
#4
Member
Thread Starter
W221s display the same issues as they have the same transmission, less two extra gears, but all are shifted by the same mechanism: the Intelligent Servo Motor (ISM). The ISM is responsible for shifting into gears and emergency operations such as forcing the car into park, if the driver's door is opened in gear and rolling is detected. With that being said, the internals of the 9G Tronic (W221s are the 7G Tronic) are the same to ~70% of transmission on the market and use the same principle for locking the transmission and driveline while in park. This method uses a parking pawl that engages on a thick toothed gear present on the output shaft to prevent rotation. Thus if the vehicle is resting even at a slight angle significant forces are present on the parking pawl and gear. To prevent this and by proxy extend the life of your ISM (even on the slightest angled surfaces): hold the brake pedal, set the parking brake, then engage the transmission into park. 90% of this thump will go away as the forces are present on the rear parking brake not the parking pawl.
However, if this thump is present on very level surfaces, your ISM and/or Transmission Mechatronics needs to be synchronized or calibrated! I forgot what it is officially called, as I haven't performed the procedure in years, but it is a very simple process with a Xentry system. I will see if my Mercedes Work Shop Information System has any documentation for the procedure.
However, if this thump is present on very level surfaces, your ISM and/or Transmission Mechatronics needs to be synchronized or calibrated! I forgot what it is officially called, as I haven't performed the procedure in years, but it is a very simple process with a Xentry system. I will see if my Mercedes Work Shop Information System has any documentation for the procedure.
