722.6 Transmission changes early

[Donald]

Have a 2003 c200 with 126k kms. Transmission changes up when especially when cold and when you accelerate it realises its in the wrong gear and clunks back. When driving along drops into 5th at 45kmh. Totally different to my SLK230. If you drive it calmly when its warm it seems OK. It becomes problematic starting ans topping and going over speed humps as it is always in a gear to high.
Local Indy has serviced it twice as oil was dirty, changed the plug and orings and no contamination. Reset the adaptive settings
Slight difference but still not acceptable.
He had a second hand valve body and conductor plate which has swapped around to isolate the problem.
Now thinking that it could be:
temperature sensors, but which ones?
MAF?
TCU?
Does TCU replacement need dealer intervention.
Any other suggestions would be welcome, could it be valve or solenoid related.

[MAVA]

Donald,

I would have not swapped the valve body or conductor plate. About four flavors exist of the valve body exist. With the 722.6 the first thing is to check the codes with MB-Star or Carsoft. You may find a non-working solenoid, leaky solenoid o-ring, or plugged screen filter on the solenoid. Check the impedance of the solenoids. Cycle the connections at the computer.

Make sure no fluid is up in the Transmission Computer.

Best of luck,

Martin

[Donald]

Hi Martin
Changed the valve body back and my mechanic put in a good second hand conductor plate to test whether it is the conductor plate.
Vast improvement.
However when it is cold and you pull up it shudders a bit as the transmission doesn't seem to drop back. Say at less than 10km/h
When it warms up after 2-3km it is fine.
Any suggestions?

[RichardM98]

Have you checked the fluid level carefully? Trans fully warmed up, car on level surface, correct 'dipstick tool', etc. 722.6xx transmissions are especially sensitive to fluid level and the correct factory approved fluid is important as well.

The transmission has built in diagnostics but you need to scan with an SDS to read them and you need an experienced MB tech to interpret them.

[Donald]

Hi Thanks for the comments

The fluid is apparently spot on.
There are no error codes.
If the valves were playing up (for example dirt or debris) presumably there would be no error code. Would that be correct.

Cheers
Donald

[MAVA]

Donald,

Like Richard said, Fluid and filter is okay. This is a young transmission for 128,000 Kilometers on it. What I would do is :

1) Replace the two o-rings in each solenoid. I believe Mercedes does not sell them(do not quote me). You may have to get the solenoid o-ring kit from a third party vendor. Because the "Golden Rule" all o-rings disturbed must be replaced-this is very true for criticle ones like Fuel injectors,torque converter, and these shift solenoids.

2) Since all 722.6's suffer from pressure leakage of the shift pistons, but 2 to 3 piston is the worst. The solution is to get a better seal, but the best practical way to fix that is from a third party vendor named Sonnax in the USA. They make a piston kit with o-rings for all the shift solenoids for about 70 USD

722.6 ValveBody Sonnax Kit Install.AVI - YouTube

Part Number 68942-05K

Sonnax - Aftermarket replacement transmission, torque converter, and high performance automotive parts[make]=11&filter[unit]=221

Sonnax - Aftermarket replacement transmission, torque converter, and high performance automotive parts

Download the valve body lay-out PDF

http://www.sonnax.com/downloads/valve-body-layouts/VBL-Mercedes-722-6.pdf

3) I would inspect each piston/sleeve assembly for broken springs

4) I'd measure the impedance of all the solenoids, and swap the upper shift solenoids with the lower solenoids as the video shows.

Hope this helps,

Martin

[Gilly]

The upshift will be delayed with the engine cold to help warm up the catalytic converters. I am confused by the description of the problem, so no clear idea if this is what is being described.
Do you notice a difference if you switch from W to S mode?