My MB E320 Sedan Story, a.k.a. ‘My 722.6 Story’
This month we make a temporary departure from the traditional Torque Converter Tech Tip article. Instead, we offer a different perspective: a torque-converter story as experienced and told by the vehicle owner. In our business we wrestle with the technical side of completing repairs and we all try to remain focused on the fact that some individual, outside our industry, owns and drives that vehicle. This gentleman not only had the motivation and determination to resolve a multi-year ongoing problem but also was willing to make a 15-hour drive to take the vehicle to a shop that he believed could fix that problem. We let him tell it in his own words.
The Importance of a Positive Seal: 722.6 Issues
There are at least two major issues that are caused by the lack of a positive seal in 722.6 converters. One issue is the shutter on TCC apply and the other is insufficient or no cooler flow. These seemingly unrelated complaints share a common cause, but the cause-and-effect relationships are quite different.
Sensor signal? Nearly none, but unit still worked
The customer had multiple concerns: 30-40 mph is the top speed, drive modes won’t switch, neutrals out in reverse, stuck in low gear at times, can’t shift manually, only works in drive Stored DTC 2767, Component Y3/6n3 (speed sensor) is faulty.
Are We Listening?
I heard a report recently on NPR (National Public Radio) that said, “Doctors are not good listeners; that is why a lot of unnecessary tests are done.”
When I heard that I said to myself, “That is true in our field too.” If we don’t listen well to the patient we may misdiagnose. Let me tell you about something that happened to me just recently that emphasizes this point. We had a customer sent to us by a local general-repair shop. He was a student here for the winter break visiting his family and was about to leave when he started to have transmission problems on his 1998 Mercedes M320.
722.6 Cold Stall/Shudder, Part II
In last month’s article, technicians found that centrifugal force acting on oil trapped between the TCC piston and cover in the 722.6 converters was applying the clutch on cold startup. They also learned that the cold-stall issue could be eliminated by forcing the oil out of the cavity between the piston and cover. Finding the root cause of the cold-stall issue – and the subsequent fix – solved many other customer complaints and symptoms, including downshift shudders and tugging sensations.
Mercedes 722.6: Cold Stall/TCC Shudder
For several years, technicians have been trying to solve the mysterious cold-stall issue in vehicles equipped with Mercedes 722.6 transmissions. When the problem was first identified, it was thought to be associated with aftermarket components. At that time, no one had seen the problem in a vehicle that still had only original equipment.
ABS – Another Bewildering Story
Well, I have two bewildering stories to share with you that normally would give you nightmares. However, by reading this story you will see that it really was another man’s nightmare. But for you it will be a sweet dream, since you will acquire his experience and bypass the pain he suffered.
The 722.6 Shift Strategy
With the 722.6 being a transmission that shifts from clutch to clutch, smooth shifting requires proper shift overlap. To accomplish this task, a number of components and strategies merge to allow for adaptation under various driving conditions. To fully appreciate what it takes to make for correct shift timing and shift feel, it is good to look at and understand these components and strategies independently. And after having a basic understanding of them, one can see how they work together like members of a musical band to harmoniously accomplish the task at hand.