Question and Possible Fix for 722.9 Transmission Jerk From 2-3 When Cold
 

I have the ubiquitous 2-3 transmission jerk/jolt when the engine/transmission is cold (in my CLK550). In the C32 AMG forum (722.6 transmission I believe), there is a thread where people reported success replacing a single TCC/PWM solenoid. Here's the thread: https://mbworld.org/forums/c32-amg-c...-solved-8.html

Upon further research of the 722.9 transmission, it looks like there are two possible equivalent solenoids:

A "working pressure control solenoid valve"
A "torque converter lockup clutch control solenoid valve"

Are one or both of the above solenoids the same as a TCC/PWM solenoid?

Please forgive my ignorance if this is a stupid question. I'm just trying to solve this issue to the best of my ability.

Thanks to anyone who might be able to provide some direction on this!










722.9 transmission control module diagram: https://www.drautotech.com/auto-serv...epair-tcm-tcu/

https://cimg4.ibsrv.net/gimg/www.mbw...cd88597336.jpg

I would suggest that you go back to the original poster and confirm as what you surmised does not make sense.
A true test of what needs repair would not be the FUYAA approach, but finding someone with MB XDOS who can give you a true diagnosis of your transmission.

Thanks for the reply. Why do you assert that replacing the TCC solenoid doesn't make sense, particularly when it worked for multiple other people (just in a different transmission)?

Also, I had my indy mechanic look at it (an ex-Mercedes technician with the Star diagnostics system) and he speculated one of the clutch packs may be bad (but he stated there was no way to really know for sure) before tearing apart the transmission. But since replacing the TCC solenoid is way cheaper, I figured it might be worth trying before going the more expensive route (or selling the car altogether rather than spending thousands of dollars to fix what is currently a very minor issue).

According to ATRA Technical Bulletin 1084, the 722.6 PWM solenoid controls torque converter lockup. Solenoid Y3/8y8 on the diagram you posted controls torque converter lockup. If the shift is harsh and the PWM solenoid is presumed to be the culprit, it suggests the lockup clutch is erroneously locked up rather than open, which would allow the torque converter to facilitate a smooth shift.

Thanks for confirming the corresponding solenoid, that's definitely helpful.

If I read your reply correctly, you're stating that the PWM solenoid is unlikely to be the culprit? That is contradictory to the outcomes of at least three separate people in the post I linked to. I figured it might be worth a try for a few hundred dollars whenever I get my transmission fluid changed.

I have been doing the same thing as you I think. Pretty sure I'm gona have my mechanic watch this video before doing regular tranny service. Gona get the kit from FCP euro to upgrade the pan and also grab 2 of each color seleniods and have him at least replace the tcc and pwm. Top right two from what I found. Couple of extras in case the cleaning doesn't get a few looking good. Let me know what you think of the plan.

Pretty impressive video. It tells me the HCU is an item needing service at high mileage. I'm intrigued by the number of magnets to be cleaned and the susceptibility of the valves to metal shaving debris.

I don't see any red flags in the procedure. If you have a high mileage 722.9, valve replacement with OEM parts seems a reasonable approach.

Drivetrain, specifically transmissions, seem to be the critical component to running a vehicle to high mileage, well over 200,000 miles. Very little is provided to consumers by car companies for maintenance at this level of mileage. Through experience it can be found that this type of transmission maintenance is important. Other vehicle forums provide similar wisdom, that transmission maintenance is important for high mileage longevity.

reason for valves andmost hydraulic parts hating dirt let along metal you can see is that clearaces between valve spool and body are very tight and much smaller then dirt.
SO dirt makes the valves stick.

Would this help with the feeling of being on constant throttle, then pushing it and feeling like the transmission has slipped?