As you can see on my signature I have two X5s with 6hp26 tranny.
The 4.4 has the well known 2-1 bang problem when accelerating before going to a full stop and a harsh up shift 1-2 in cold mornings. Otherwise the transmission is smooth like new.
The 4.8is got the same problems plus a harsh shift 2-3 or 3-4 (not sure) when accelerating fast from a traffic light. In normal driving this problem is not happening. The harsh up-shift 2-3/3-4 felt like the clutches were braking for a split of a second. I don't know how to describe it well.
My wife wouldn't feel any of these on the 4.8 but it bothered me so I had to do something.
Over the last two years, I did the firmware update, 4L oil change and filter but it didn't feel like it fixed anything or not significant. Last year, I changed the square and cylinder VB rubber seals and again the tranny was not as smooth as some of you found after these changes.
A week ago I changed the solenoids (US $260.00) and so far I can say that the transmission feels like new.
The procedure is pretty straight forward and is well documented on internet.
Everything about your ZF 6HP26, 6HP19, 6HP28 transmission issues | BMW LOGIC7
https://www.youtube.com/watch?v=zwjvxRZyvWM&t=40s
Re-learning procedure after the adaptation reset
Here is the proof
