General Motors announced today that its new eight-speed automatic transmission will be standard on the 2015 Chevrolet Silverado, GMC Sierra, and GMC Yukon Denali and Yukon XL Denali models equipped with the 6.2-liter V-8. Not sharing the eight-speed love is the Chevy Suburban, which offers only the 5.3-liter V-8.
The new Hydra-Matic 8L90 is a neatly packaged gearbox; it’s roughly the same size and weight as the 6L80 six-speed that it replaces. One of the eight-speed’s key advantages is a wider overall gear-ratio spread that allows for a higher first gear, permitting easier starts when carrying a heavy load or towing a trailer. Another advantage is that the 8L90 permits taller rear-differential ratios, which drop engine rpm at highway speeds and improve fuel economy. On the subject of fuel economy, no official numbers are out yet, with EPA testing still pending.
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For those of you connecting the dots, yes, this essentially is the same transmission that will be used in the 2015 Corvette Stingray. The 8L90 in the trucks and SUVs will use the same torque converter as the Corvette’s eight-speed, but has a different case with a bell housing and extension, different mounting points on the torque converter, and different output shafts.
We expect more technical information and fuel-economy numbers to follow the closer we get to the production date set for the fourth quarter of 2014.
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