V8fella

Hi All, have recently become the proud owner of a 2012 C63 with 65k miles - overall the car is great but I have noticed the following with the transmission:
Downshifting from 4th to 3rd (in manual mode) between 1k - 3k revs results in an aggressive jerk every time. It doesn't happen when manual downshifting in C, S or S+ but sometimes on an enthusiastic drive it will happen in S / S+ automatically without me downshifting. If I apply the throttle slightly as I downshift it can sometimes counteract it and not be as aggressive.

Another issue I have is pulling off from lights I feel like the transmission is a little slow to pick up and isn't as sharp as I would hope, almost allowing the engine to rev slightly before it catches up. This is heightened on first start when the car is cold.

I did some searches and see that many people have had similar downshift issues which have been cured with a transmission fluid replacement, I have had this carried out and unfortunately it has not got rid of it,

Any thoughts or advice would be welcomed! Many thanks..

CheckOrHold

A video would probably be better to describe because these cars are supposed to have aggressive downshifts. If you drive it hard, the transmission will continue to act more aggressive even when you try to drive "normally" again for a while.

HLG600

If your 2012 C63 has the MCT version of the 722.9 transmission, you need to reprogram the shift points via Xentry after a service. Otherwise your shift quality will be crap.

https://www.weistec.com/media-events...9transmission/

roadtalontsi

The transmission automatically adapts. There is no reason to ever reset and perform adaptations unless you replaced or changed actual hardware in the transmission. It very well could be normal operation since you're new to the car. It could be tune related if it has a tune, or something else internal to the transmission. Transmission services / fluid changes dont fix problems they are preventative maintenance just like changing your oil. If you're truly concerned take it to someone who knows those cars well. Me personally I don't care for the MCT cars because they are always jerky. They shift quicker and are more responsive but at a cost I personally don't care for unless i'm on the track.

HLG600

The transmission indeed adapts automatically, but this can take a long time. Using Xentry will expedite the process.

To offer a point of reference, my MCT shifted smoothly before a transmission service and was exhibiting some odd shifting behavior immediately afterwards (including that slight "rev up and go" bit from a standstill mentioned in the OP).

After reprogramming shift points, the smoothness returned.

Good point, however, on the transmission software potentially being modified (or even in need of a factory-issued update). Something worth looking into.