Thud upon gear change when kickdown is used in a 2009 R230 SL350.

[Chrishazle]

Furthermore, this likely affirms that the 50,000-mile, 2009 SL350 I purchased has been very light on problems, since it is referred to as "SuperLicht". 🙂 Both the rotted-out fuel line and the minor C pillar leak were repaired inexpensively. Nevertheless, I must mention that I saw a gearbox problem during kickdown for the first time yesterday.

The gear shifts, both up and down, are very smooth with regular use. Even when applying significant force, the transition between gears is smooth. Occasionally, there may be a little, clumsy downshift while the vehicle is warm. Engage the kickdown feature to experience forceful and impactful gear transitions. When starting from a complete stop, the P and D gears engage smoothly and without any noise or difficulty. During regular driving, there are no unexpected gear changes or instances when the gear is held in place.

Has anybody encountered this previously? After doing an extensive search through the discussions, I have not come across any comparable information. The vehicle has not had an ATF replacement, and I am curious whether the issue is just due to the oil losing its viscosity when heated, resulting in occasional rough downshifts while the vehicle is warm.

Can anybody provide insights into the possible reason or share their experience with a similar issue?

Thank you

[bvlenci]

Has the gearbox not been serviced for 50,000 miles and 15 years?

The vehicle is significantly overdue for a servicing.

[AMG33D]

The engine mounts and gearbox mounts are significantly worn and in need of repair.

[Chrishazle]

Thank you. I assume that the fluid has deteriorated, but it is important verifying to rule out any other potential issues. The lack of performance in low temperatures may indicate a decrease in viscosity when the automatic gearbox fluid (ATF) is heated.

The gearbox of the vehicle has a complete maintenance history, as shown by the Digital SR, which shows that it was serviced at 37000. Therefore, it may be somewhat overdue for maintenance, but not excessively so.

Greetings

[Chrishazle]

I will get them examined since I was not aware that they may potentially cause problems. It didn't occur to me since it hasn't been present on any of my other vintage "Sunday" autos.

Would it clarify the conduct that occurs only when the temperature is warm or hot?

I appreciate your suggestion.

[KissezFun]

If the gearbox had maintenance at 37k, the automatic gearbox fluid (ATF) should still be in excellent condition. A mileage of 50,000 is considered to be rather modest when it comes to experiencing issues with the gearbox.
I suggest seeing an MB professional to first read the problem codes.
What is your location in London?

[Chrishazle]

The alteration occurred in 2016, and I lack sufficient knowledge about ATF to determine the extent of its degradation over time. I am located in close proximity to Ascot, which is situated to the west of London. Star Services Reading seems to be the closest expert to me, unless you have a suggestion?

Thank you.
 

[KissezFun]

Indeed, Star is an excellent choice.
In my opinion, it would be unwise to spend money on changing the gearbox ATF without having an expert inspect the vehicle for any further defects that may need attention.
If you are considering doing a do-it-yourself automatic gearbox fluid replacement for £100, or purchasing an icarsoft code reader for £100 to assist with future car maintenance, then these are viable possibilities for you.