Mercedes now uses 7-speed tranny

Motor, Nov 2003 by Nash, Tom

According to Mercedes-Benz, the world's first standard seven-speed automatic transmission for passenger cars is providing improved fuel efficiency, acceleration and ride comfort. The 7G-TRONIC seven-speed automatic transmission is now standard equipment on 2004 8-cylinder E-, S-, CL- and SL-Class models. Depending on the model in which its fitted, the 7G-TRONIC can reduce fuel consumption and shave up to .3 second off 0-to-60 acceleration. And gear changes are performed even more smoothly than with the previous unit, for greater comfort.

The new transmission features a torque converter lockup clutch, which creates a virtually rigid connection between the engine and the transmission input shaft whenever conditions are appropriate, thus preventing loss or slip across the hydrodynamic torque converter. Converter lockup engages even in first gear, unlike most automatic transmissions, where lockup will not engage before third gear.

For faster downshifting, the transmission can deploy a combined "direct and sliding multiple downshift" function. Rather than changing down sequentially, the electronic control unit may skip some gears. Therefore, in some driving situations, only two gear changes-instead of the previous four-may be required for fast acceleration under kickdown.

The 7G-TRONIC is about the same size and weight as the five-speed automatic it replaces, a result of the use of magnesium for the transmission housing.