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Mercedes Automatic Transmission

Mercedes Benz Automatic Transmission

A Mercedes automatic transmission is a fine thing, as the clutch feet and shift arm finally get a much deserved break – the technology takes care of the once uncomfortable manual gear shifts. To ensure that the automatic transmission functions as seamlessly as possible, the inconspicuous light metal housing of the Mercedes automatic transmissions is filled to the brim with high-precision mechanics.

The core is the planetary transmission

The core of a Mercedes automatic transmission is the planetary gearbox, it is a large gear with inner gearing (hollow wheel), which interlocks with an eccentrically arranged solar wheel, circling with three to five gears (planet wheels). The trick: Depending on the braking or driving of any of these five gears, the automatic transmission can be realized with a planetary, set up to three gears.
This means that a Four-stage automatic transmission requires at least two planetary sets. Because there are overlaps in the translations, three planetary sets are needed for five gears, and four for six gears.
The planetary gearboxes are switched with lamella couplings and brakes. These consist of stacks of Fins, which alternately have internal and external gearing, and run in the oil bath of the gearbox. One type of slats, usually those with the internal teething – is coated with friction linings. If the slat packages are compressed, they can transfer forces. This is achieved via a hydraulic system, the pressure of which is generated by an oil pump. This sits at the front of the automatic transmission, and is driven by the pump wheel of the torque converter – so it runs constantly at engine speed.

The “brain” of the automatic transmission

The real brain of a Mercedes automatic transmission is the shifter box. Its channel system – which is actually reminiscent of brain coils – it determines how lamella couplings and brakes are actuated and thus the gears are switched. This works with the automatic under load, i.e. without interruption of traction by uncoupling. Because the well-oiled lamella couplings can also work under slip for a short time. The transition from the open to the closed clutch is smooth, while the other opens at the same moment.
In the past, the control system was purely hydraulic, and for about 20 years, electronically controlled valves and controllers have also been involved. Thus, a more precise coordination of driver temperaments on one hand, and low consumption on the other hand is feasible. Nevertheless, the efficiency of an automatic transmission is lower than that of the manual transmission. Thankfully, modern automatics compensate in part by clever shifting strategy. They also drive in the city in the highest gear, let the engine pull at low speeds, and use the force gain of the torque converter.

Wear and maintenance of Mercedes automatic transmission

The planetary sets do not break so quickly, unless you have too little oil in the automatic transmission. So always check the gearbox oil level, or perform a gearbox flushing. Other wear points for automatic transmissions can also be the brake bands, which brake the individual planetary sets, or the torque converter which establishes the power connection between the engine and the automatic transmission.


However, if chips are already visible in the oil pan, it must be expected that these chips are located throughout the oil cycle and in the converter. In this case, the automatic transmission must be completely replaced alongside the torque converter. More on this.

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