Howdy folks.
2008 s550 4 matic 120k miles.
I feel like there is a slight hick up from 2-3 shift at light throttle. its like a little uncertain stumble. Only at light throttle. Otherwise its fine in all other gears. And its fine if I apply more than 30% throttle input.
Friend at MB hooked it up to MB system it it didnt show anything bad. The clutch wear was at 800 I believe out of a 2000+ or- Range. He assures me that is normal wear for the miles.

I have MB records for the car from new, 6-8 pages, in it there are no records for trans fluid change. I cant decide if its a good idea to change fluid at 120k miles. I am afraid of things getting worse after it and not better.
Naturally I dumped thousands of dollars over last 3 years, $2000 just this summer and would like the car to last another 30-40k miles as I barely drive it, weekend car mostly. Id hate to dump another 4-5k into it if trans goes. Car is mint otherwise.

Advice is appreciated.

Thank you in advance.

 

change the fluid - it should be due it fourth change at 120k miles

very cheap - and easily the simplest next step

 

Change the fluid and filter but don't (force-)flush it.
Most problems occur after a forced flush of the system (it dislodges dirt that should just stay where it is).

 

Thank you.
Will change oil soon.

 

It sounds like you're dealing with a classic scenario where slight transmission issues can often be attributed to wear and tear or fluid degradation, especially given the mileage on your S550. The shift hesitation from 2-3 at light throttle could potentially be the result of aging transmission fluid, which may have lost its effectiveness in lubricating and maintaining proper hydraulic pressure for clean gear shifts. Even though your friend's diagnostic didn't show immediate flags and the clutch wear appears normal, the transmission fluid might not be performing optimally anymore. While Mercedes claims lifetime fluid in some models, changes are generally recommended around the 60-100k mile range, especially if no fluid service history exists. There's always some risk involved with changing high mileage fluids, mainly if sludge buildup might relocate. However, the stumble you described could very likely be mitigated, if not resolved, with a refreshed fluid service, possibly including a filter and pan gasket change. For a more thorough diagnosis, I recommend checking the Transmission Control Unit (TCU) for any stored or pending fault codes that might not have triggered a CEL but could indicate adaptive learning limits, solenoid performance issues, or hydraulic pressure anomalies. If you're considering a DIY approach, a full system scanner like the youcanic is invaluable for such cases as it reads all vehicle systems. Be wary of using basic scanners like the Innova 3100j, which mainly reads engine codes and might miss transmission-specific fault codes. Investing in this deeper read could provide insights without misleading data and help with any adjustments post-fluid change. Before proceeding, have you looked into whether the adaptive transmission settings need recalibrating? Sometimes, resets or adaptations can resolve subtle shifting irritations.

 

on the 7g rear drive box
they pretended its was fill and forget and they dropped like flies way before end of warranty
they moved to a one off 42k mile change
that wasn't enough and it moved again to every 37 k miles

if u have filth destroying your box get it out
pretending swarf and sludge is better is insanity
double check what they do with 4x4

 

I think your tranny should have fluid change every 40 000 miles so if it has never been changed please do yourself a favor and have it done.

 

Thank you.

Will change fluid soon. Funny thing is, now that temps are in low 30s, trans is perfect and very crisp.

 

Right, because the trans fluid is a little thicker at colder temps like now resulting in slightly higher pressures making a nice crisp shift. Since your fluid is also old and past its normal life, it is also probably a little thicker. I agree with all the good advice you have read here and hope you consider doing a fluid and filter change. It will shift crisply with new fluid. Keep us posted.

 

Like vettebk says the colder temperature probably cause viscosity change higher and tranny works better. Oils typically get thinner over time and then in a tranny flows and pressures change.

Change your fluid before you destroy the clutch disks packs inside the tranny.