The Mercedes 722.9 Transmission, a 7-speed automatic transmission, was widely used in Mercedes-Benz vehicles from 2006 to 2017. Known for its ability to skip gears during downshifts, providing a sporty driving experience and quick response, this transmission boasts seven forward speeds, balancing aggressive acceleration with fuel efficiency in higher gears. However, the 722.9 transmission has also been associated with shifting issues.
Early models, particularly those with converter-based AMG variants, often exhibited slow and sluggish shifting, along with harsh downshifts when coming to a near stop. Mercedes has addressed these concerns over time through software updates and new transmission fluid formulations. Despite these improvements, shifting problems can still arise due to transmission adaptation issues or hardware malfunctions like a faulty Transmission Control Unit (TCU) or clogged solenoids.
The Adaptive Nature of the 722.9 Transmission
The TCU in the 722.9 transmission continuously self-adapts by adjusting clutch pack fill times and pressures to compensate for variations in manufacturing tolerances and clutch wear. This ongoing adaptation process is typically slow, as changes in fill times and pressures should only occur gradually as the clutches wear. A sudden change often signals a premature hardware failure requiring repair rather than adaptation. Consequently, achieving optimal shift quality after replacing transmission components can be a lengthy process due to the slow self-adaptation.
Rebuilding and Upgrading the 722.9 Transmission
A transmission requiring a rebuild has likely undergone extensive self-adaptation to compensate for slipping clutch packs by increasing fluid pressure and adjusting shift operations. These stored adaptations within the TCU can significantly impact shifting performance after a rebuild. A freshly rebuilt transmission, with tighter tolerances and quicker responses, may experience harsh shifting or shift flaring if the TCU operates based on the old adaptations. Therefore, clearing all adaptations when installing new internal transmission components, whether using OEM or aftermarket parts, is crucial, following Mercedes service procedures.
Regardless of the type of clutch packs used in a rebuild – OEM, performance upgrades, or a complete transmission replacement – adhering to Mercedes’ fluid filling and transmission adaptation procedures is essential. Driving a high-powered or even a stock vehicle aggressively before completing the adaptation process after a rebuild can immediately damage new clutch packs, necessitating another rebuild.
Resetting Shift Adaptations with XENTRY
Resetting stored shift adaptations requires a Mercedes XENTRY Diagnostic Tool. This straightforward process resets all values to zero, allowing the TCU to adapt to the new hardware without interference from previous adaptations.
Forced Adaptation for Optimal Performance
For optimal performance after a rebuild, especially with performance upgrades, forced adaptation using the XENTRY tool is recommended. This process involves following on-screen prompts within XENTRY to execute specific shift patterns under defined conditions. Each successful adaptation is confirmed with an audible beep, ensuring accurate data collection for each gear change. Forced adaptation significantly reduces the adaptation time compared to relying solely on normal driving conditions, which can take hundreds or even thousands of miles.
Accessing 722.9 Service Data
For detailed information on Mercedes-Benz recommended procedures for the 722.9 transmission, including drain and fill procedures, adaptation resets, and solenoid cleaning instructions, consult the Weistec 722.9 Service Data document. This resource provides valuable insights for maintaining and servicing this complex transmission system. (Link to document would be placed here if available).
