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Michael Warfield
Michael Warfield, Factory Mercedes-Benz Technician
Category: Mercedes
Satisfied Customers: 3130
Experience:  Mercedes-Benz Master Certified technician
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why does my transmission make a clunking noise when downshifting

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why does my transmission make a clunking noise when downshifting from 2 to 1 or up from 1 to 2 after it gets hot from stop and go driving? Sounds like rear end joint or overdrive not disconnecting.
What is the year and model of your car?

Edited by Michael Warfield on 9/12/2010 at 12:02 AM EST
Customer: replied 6 years ago.
2003 CLK 320 MB, 75k miles.
It definitely seems like the valvebody might be causing a sudden immediate upshift or downshift causing this noise. I would suggest having a european shop or dealer perform an adaptation on the transmission to possible improve shift quality. If it doesn't, only then would I consider replacing the valvebody.
Customer: replied 6 years ago.
Does the valve body control the locking mechanism?
Are you talking about the shift lock?
Customer: replied 6 years ago.
Maybe if I can describe the problem better. When the engine and transmission are "cold" there is no clunk sound. If I drive for an hour in rush hour traffic then come to a complete stop there is a clunk sound right prior to stopping. Then when I start driving again (from a standstill) there is a loud clunk sound when it tries to shift from first to second. If I use the manual shift and allow the engine to rev past 2500rpm I can avoid the clunk sound. I think transmissions today have a torque converter lock that directly locks the engine to the drive train so that is what I meant by locking mechanism. Or maybe I am old school and have no clue about transmissions today.
The valve body controls the torque converter lock up clutch. Transmissions haven't changed much, except for the electronic controls. The valvebody is shifting applying the gear too fast or at an incorrect time causing the clunk, not the torque converter lock up clutch. You can adapt the gear with a computer which tells the transmission how fast to apply the gear. If the adaptation is out of spec or if there is a fault stored in the transmission computer, it could cause this sudden jolt/knock noise of the driveline. I would suggest having the fault codes read, transmission fluid level and condition checked, and then possibily having the adaptation performed.
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