jrox

Hi, I've seen similar posts but nothing quite the same from searching through. I've had my 2011 C63 estate (facelift with newer gearbox) with performance pack since almost new, from Brooklands in Surrey. It's been perfect for years until the last couple of years a fault started to develop. Nothing is reported on diagnostics apparently and the car is fully MB serviced to date. I've had the torque converter replaced as that was the belief as to the cause of the issue. Driving below 2000rpm and lightly pressing the accelerator there is a stutter or erratic engine revving. It's hard to describe, but it sort of drops and rises as if it's trying to shift gear but doesn't until you press a little harder and then it shifts down and seems ok, but often it's a bit of a clunk when shifting.

It revs fine in neutral, no sign of misfire, when you give it full beans to overtake etc the engine seems to pull hard but the shifting is slower than it used to be and sometimes it feels as if something is almost slipping before it really puts the power down. There's now a thrumming through the bodywork when it's "struggling" and it's driving me insane. The gearbox has been flushed through and oil replaced. What I noticed the other day was even more interesting. Driving along a quiet dual carriage way I noticed that it appeared to be struggling with shifting again each time I touched the throttle. Before, I could put the car in sport or sport + or manual and it would stop happening. Now it's happening more in sport as well. Sport + not so much but then it's always in a lower gear and often just above 2000rpm. So as a test I was doing around 60mph in manual in 6th to ensure it was below 2k rpm. Then a light touch of the throttle to "keep up with the traffic" and while the road speed appears to increase the engine rpm seems to jump and then settle down again and it's fine. I wonder if even though it's showing it's in 6th in manual it's actually trying to shift down but failing. Perhaps it's some sensor that's failing, but it's an odd feeling and I'm really starting to get frustrated with that car. I hate that as I loved this car and it's been sensational and faultless up until now. It's become jolty in traffic, seems to be sluggish at low RPM, smells quite hot even after a short journey but the engine and oil temps appear fine.

(recorded by my wife in passenger seat while on a 70mph dual carriage way) You'll need volume up to hear the revs rise almost as if it's changed down but hasn't.

I've spoken to MB and they seem to think it runs beautifully... Got to be kidding, I really wonder if they know what they're talking about sometimes. There's clearly something wrong but even a specialist couldn't put their finger on it and we therefore started with the torque converter as it seems to be "slipping". Next was the gearbox, but I can't throw another 3 grand at the car just like that. It's got to be something electrical I would have thought, some sensor or something trivial like that.... I struggle to see how the gearbox could be causing this. I did wonder if the differential might be something to consider, perhaps it's faulty and when a load is applied it's moving on it's mounts or there's wear in the gearing that's causing some shuddering and confusing the sensors.

I'll try and get my wife to video what happens at slower speeds next time too. Such as in Comfort and driving in traffic around 30 to 40mph and rpm is below 2000 and the rise fall rise fall rise fall rise fall of the revs as it's almost searching for the downshift but it's not happening...

The rumble/thrum through the car when this happens perhaps indicates something lose of vibrating but no-one seems to be able to help at all. I've also noticed that sometimes in Sport mode if I manually override the gear selection with the paddles it appears to get stuck in that gear. So in sport or sport + you can override with the paddles and it'll show you the gear selected in the little box and by pulling the paddle for a few seconds it goes back to full auto. Well it returns to full auto and the little box with the selected gear disappears but it doesn't then shift gear itself it just sticks in that gear and doesn't appear to want to change up again unless I spin the gearbox settings wheel back to C.

The car has had no modifications from factory and has done 73k miles now. Been perfect until a few years ago when this first started. Progressively getting worse and more and more frustrating. I appreciate it's an old car now and perhaps that's the simple issue, she's just too old and long in the tooth but I've tried everything to keep her in great condition and when she goes, wow does she put a smile on your face still after all these years.

Thanks so much!

PP-PRO_C63

I also have this problem with my C63. Similar to your performance, I also have the problem of slow start. When I let off the brake, the car doesn't squirm quickly, but has a very hard, sluggish squirm that's very slimy and clunky.
This bothered me for two full years. I strengthened the internal friction plates of the gearbox and restructured the gearbox. I also bought a new valve body and a torque converter remanufactured by Mercedes-Benz. Finally, I determined that the main problem was with the gearbox. on the torque converter.
But the Mercedes-Benz remanufactured torque converter I purchased seems to have quality issues. It only successfully completed the wet clutch clutch point learning in one match (I drove it after that clutch point learning, which was something I had never experienced before. Sensitivity training, as long as I put the D gear on and release the brake, the car quickly starts to creep into the state without any sluggishness, and when I step on the accelerator at any speed and gear during driving, the acceleration is very smooth, just like everything in the engine The power is completely transmitted to the rear wheels instead of being consumed by slippage in the torque converter), but because I reorganized the gearbox and cleared the original shift data, there are some problems with the current shift. I later learned the clutch point and Shifting gears, for some reason, the torque converter returned to its original state.
My mechanic told me that it's possible that the Mercedes-Benz remanufactured torque converter itself has some quality issues, which he said is not uncommon. I will buy a brand new torque converter in a while, install it and learn the matching again, hoping to completely solve this problem.
The above is for your reference.