Clunky transmission sometime and today it did slip for the first time - Mercedes-Benz Forum
 
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post #1 of 10 (permalink) Old 03-20-2019, 06:00 PM Thread Starter
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Clunky transmission sometime and today it did slip for the first time

My wife has been complaining for some time about her 1999 CLK's transmission being clunky sometime. Her car otherwise is in pristine condition with only 60k miles on it. She told me the clunk mostly happens when she decelerates and at low speed. Today she had a more serious problem. She said she was moving very slow in traffic moving on the momentum and when she pressed the gas pedal again the engine rev without pulling the car. She tried different gears to no effect. Then the transmission clunked and the car worked fine after that with no more clunk and she was able to do the rest of the trip home in traffic. I am thinking of a problem with the torque converter. I checked the ATF level and it is within the specs. While the car does not have that much miles the transmission fluid looked pretty brown. I am pretty sure it was never replaced since 1999 so I ordered a new filter and seal and will replace the transmission fluid this week-end. Do you think that a dirty ATF could be the cause of this problem and that with a bit of luck replacing the ATF will fix the issue? I mean could a torque converter go bad after only 60kmiles? Any input would be appreciated.
By the way here is how I do my transmission fluid change. I put the car on stands, drain the gear box, drop the pan, change the filter, put the pan back, refill with the same amount of ATF that I drained, go through all the gear while the car is on stands, drain the atf again, refill, go through all gears, drain one more time and at that time the ATF I drain is clear red which tells me that I have replaced the entire ATF.
Thanks folks
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post #2 of 10 (permalink) Old 03-21-2019, 01:54 PM Thread Starter
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I took her car to work today. The car operated perfectly on the 8 miles trip to work this morning. However this evening on the way back from work I was decelerating going may be 20mph and when I pressed the gas pedal again the car went to first gear and the engine rev quite a bit as a result before going back to the appropriate gear. So it feels like the gear box gets confused sometime with what gear it should be in.
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post #3 of 10 (permalink) Old 03-21-2019, 03:26 PM
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Hopefully its something simple, did you try the transmission reset procedure? The transmission on these are really easy to replace and readily available if its the worst case scenario

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post #4 of 10 (permalink) Old 03-21-2019, 05:24 PM
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When properly maintained, the mechanics of the 722.6xx transmissions have proven to be extremely reliable. Most issues were electrical and preventable with proper servicing.

Initially, because the factory fill was synthetic ATF, our owner manuals state that the transmission would never need servicing.

As some problems began developing (e.g. clutch and gear wear deposits clogging the filter and/or the conductor plate's command or regulating shift control valves), MB began recommending that the transmission be serviced (e.g. of filter and ATF) at 39,000 miles and every 39,000 miles thereafter.

Also check if your pilot bushing is leaking (e.g. which could wick fluid into the TCU) and if so, replace it with the updated part.

Another possibility is that your transmission range recognition switch, in the center console shift control module, may be intermittently sending an erroneous signal to the TCU. A common failure was caused by moisture, which was corrected in April 2001, when a new moisture resistant part became standard. I'm pretty sure that a DTC is not stored in this situation, which may be why the system did not go into safe mode.
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post #5 of 10 (permalink) Old 03-22-2019, 12:26 PM Thread Starter
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This morning I replaced the transmission fluid, filter and gasket. There was quite a bit of sludge at the bottom of the pan and the transmission fluid was really brown. I went for a drive and the car did ok but after 25mns of driving I got the same problem again. I was stopped at a traffic light and when I took off the transmission stayed in lower gear, I guess second gear, and did not gear up.This time it triggered an engine light. I drove like that for 10mns around 40mph with engine reving around 4k. I stopped, turned off the car for 5mns and when I took the car again it worked fine. back home i read the codes and there were p0715 and p0700
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post #6 of 10 (permalink) Old 03-22-2019, 03:51 PM
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P0700 and P0715 are only generic Diagnostic Trouble Codes (DTCs), which when using OBD II scanners, only see that the TCM or ECM did not receive the proper signal from another module or sensor.

BTW, that's because the W208 and W210 did not implement full OBD II (only provided +12 volt, ground and a single ended K line).

Significantly more detailed DTCs and diagnostic information is available with the MB STAR Diagnostic System (SDS), that connects to the 38 pin diagnostic connector in the engine bay.

When either a mechanical or electrical malfunction is detected, these codes are stored and the vehicle will go into limp-home-mode.

Electrical limp-home mode:

In order to prevent damage to the automatic transmission in the event of an electrical fault, the gear currently engaged is held and the assigned diagnostic trouble code (DTC) is stored.

The limp-home mode comes into effect with the following procedure:

1. Stop vehicle.
2. Shift transmission selector lever to "P".
3. Shut off engine.
4. Wait at least 10 seconds.
5. Start engine.

After restarting engine, the vehicle can only be driven in 2nd or reverse gear.

The engagement of "N->D" and "N=> R" will be very harsh, since the electronic control of the automatic transmission has been turned off.

This type of limp-home mode can only reset by repairing the fault and erasing the DTCs.

Mechanical-hydraulic limp-home mode:

In order to prevent damage to the automatic transmission in the event of a mechanical-hydraulic fault, the transmission shifts into 3rd gear and is held in this gear or the transmission shifts to the last "known good" gear and is held in that gear.

This type of limp-home mode is reset by turning the ignition OFF and then ON again.

BTW....I recall that MB lost a class action suit, because very early production W208s were not filled and/or serviced at dealerships with the proper synthetic fluids, which then caused sludge buildup and unnecessary repairs.
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post #7 of 10 (permalink) Old 03-27-2019, 05:23 PM Thread Starter
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Thanks for your last post serndipity that helps. So here is an update. The car had not been used for the last 4 days but this evening I did the transmission reset procedure which to my surprise turned off the engine light. I then drove the car for about 1h both in traffic and on highway and the car drove beautifully, transmission switched gears smoothly. I tried all gears manually too and no issue. I am going to keep driving this car for the next several days, go to work with it and drive it around to see how it goes because I am not sold yet on the issue being fixed. I dont want to speak to quickly and we will see in the next few days if the car keeps working fine but if it does I am not sure what happened. May be some of the sludge I found at the bottom of the pan may have clogged the solenoids and possibly fresh ATF clean them? If the problem comes back my next move will be to replace the conductor plate and connector and test the solenoids. I never did it on any of my Benz's but it does not look like that complicated based on the videos I found on line and if I take my time. It looks much easier than replacing the 12 hydraulic cylinders of my old SL's soft top which I did few years ago.
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post #8 of 10 (permalink) Old 04-09-2019, 05:27 PM Thread Starter
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The car has been driven every single day for more than 2 weeks now and no more problem. It drive very nice and gears shift very smoothly. I suspect the dirty fluid and sludge was the issue.
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post #9 of 10 (permalink) Old 04-10-2019, 12:29 PM
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Great....seems that you got the ATF and filter maintenance done in the nick of time.


BTW, these forums also have a treasure chest of information for diagnosing, troubleshooting and repairing the A208 power soft tops as well.

As example: https://mbworld.org/forums/clk-class...ailures-9.html
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post #10 of 10 (permalink) Old 04-10-2019, 01:58 PM Thread Starter
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Quote:
Originally Posted by serndipity View Post
Great....seems that you got the ATF and filter maintenance done in the nick of time.


BTW, these forums also have a treasure chest of information for diagnosing, troubleshooting and repairing the A208 power soft tops as well.

As example: https://mbworld.org/forums/clk-class...ailures-9.html
Thanks again and yes this forum and the others are invaluable. Without them maintaining my 4 cars would be a big challenge.

Last edited by alpac; 04-10-2019 at 02:03 PM.
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