722.6 lock-up clutch slipping (never closed) - Mercedes-Benz Forum
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post #1 of 11 (permalink) Old 06-27-2017, 12:30 AM Thread Starter
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722.6 lock-up clutch slipping (never closed)

I hooked up a computer to my 722.6 transmission and found that the torque converter never locks. Can anyone advise on this, please?
Basically, when the gear is in park or in neutral, the computer shows: Lock-up clutch is open (image attached), but while driving, it is always "slipping". I drove the car on the highway at 70-75 miles/h (110-120 Km/h) and never got the torque converter to lock.
I am inclined to flush the transmission fluid especially at 136K miles (218K Km) with no reference of this service in my records from the previous original owner.

Any help is appreciated.
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post #2 of 11 (permalink) Old 06-27-2017, 05:47 AM
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Poster MAVA has great depth on these transmissions.
While you wait for his advice take a read at this thread and download the information. Plenty to pour over.

https://www.benzworld.org/forums/w140...ce-manual.html

Skippy

Skippy,
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post #3 of 11 (permalink) Old 06-27-2017, 09:31 AM
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Suppose those cruisers lock the converter above 80 mph, but on my diesels I could not see that happening even at those speeds.
Nothing you can do about it.


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post #4 of 11 (permalink) Old 06-30-2017, 06:05 AM Thread Starter
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Quote:
Originally Posted by SkippyJasper View Post
Poster MAVA has great depth on these transmissions.
While you wait for his advice take a read at this thread and download the information. Plenty to pour over.

https://www.benzworld.org/forums/w140...ce-manual.html

Skippy
Thanks for pointing this out. Although it has a lot more than I have wanted, it is really useful. I will have to spend a long time until I find an answer to lock-up clutch question!
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post #5 of 11 (permalink) Old 04-25-2019, 12:31 AM Thread Starter
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Just to have a closure to this thread, I went to an expert transmission shop. They hooked up the computer (the same one I used myself), which was not a star but an aftermarket Chinese knockoff. We went on a lengthy test drive. The guy said the tansmission was in great shape and that the torque converter locking was working fine. Their computer did show "slipping" all the time, but the guy said I should ignore that because the computer was not specific for MB. The guy said he could feel the locking after each shift if the car is not accelarating.
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post #6 of 11 (permalink) Old 04-25-2019, 07:02 AM
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Originally Posted by ezzo View Post
Just to have a closure to this thread...The guy said the transmission was in great shape and that the torque converter locking was working fine. Their computer did show "slipping" all the time, but the guy said I should ignore that because the computer was not specific for MB. The guy said he could feel the locking after each shift if the car is not accelarating.
Interesting. Mine behaves in the same manner when I look at my diagnostic computer. Mine feels OK though, FWIW. I've got other valve body issues due to dirt over time, but that is another story.
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post #7 of 11 (permalink) Old 04-25-2019, 07:19 AM
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it is usual...

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post #8 of 11 (permalink) Old 04-25-2019, 07:47 AM
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With a proper scan tool you should be able to shut off the lockup torque converter and compare the bahavior. The most likely failure point is the lockup torque converter solenoid. The 722.6 locks the torque converter in every gear including first. This is very unusual for an automatic. The result is that that lock out solenoid (TCC) gets worn out much faster than every other solenoid in the transmission. If you're doing the conductor plate I suggest also replacing the TCC solenoid. It's a $28 part on fleabay.
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post #9 of 11 (permalink) Old 04-26-2019, 05:39 AM
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There are many factors influencing TC lock. Engine load being primary. Is is easier to observe transition from open to slipping to closed in 3rd or 4th gear.
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post #10 of 11 (permalink) Old 04-30-2019, 05:35 AM
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i did this same test with DAS before i replaced my torque converter and rebuilding my valve body, and noticed no change in the numbers running the test AFTER changing the torque converter.

My torque converter itself however, had severely worn lockup clutch material and an intermittent stator clutch causing all kinds of weird behavior. a new torque converter restored normal driving behavior and smoother driving.

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