Mr. J

Vehicle is a 2017 GLC43. Frequently I'll use Eco mode on highways and freeways with hills or mountain passes. Sometimes when coasting in Sail mode for extended distances the transmission will downshift roughly as it re-engages. This mostly seems to happen on extended downgrades and when downshifting to 7th gear or lower. The rough downshift is enough to jerk and decelerate the vehicle similarly to downshifting 2 or more gears in a manual without rev matching.

Has anyone else encountered this issue? I've complained about it at my last service appt. I'm due for another routine service soon.

ajmtbm

i have a 2017GLC300 and had an issue where if i let off the gas then needed to press the accelerator the transmission would get wildly jerky. the dealer found there was a software update available and that solved the problem. not sure if would be same for the 43 but may be worth of ask. maybe also search ther forum, i think there may have been a thread and some discussion on it some time back

AlphaEagle

I had that issue (or a similar one) where when in sail mode and coasting at highway speed (60 - 70mph) the car would "sail" for maybe 15 seconds then I'd get this weird clunking sound as the transmission forced itself back in gear. It happened over the course of a summer when I had only a few thousand miles on her. It fixed itself and hasn't duplicated the issue for more than a year and a half.

Mr. J

This sounds very similar to what mine does. The only difference is that in my case the car is typically in sail mode for a longer period.