Photo: Chevrolet
As it transitions from GM's 6L80 six-speed automatic to the new 8L90 eight-speed, the 2015 Chevrolet Silverado 1500 with the 6.2-liter V8 engine will maintain its 12,000-pound maximum available trailer weight rating. The eight-speed auto update promises improved fuel efficiency and smoother shifting.
With great regret for those that are pondering about buying such a pickup truck, GM tells that EPA-estimated fuel economy of the updated drivetrain "will be announced closer to the start of production in the fourth quarter of 2014." By comparison, the same 8L90 gearbox fitted to the 2015 Chevrolet Corvette Stingray improves fuel economy on the highway by 3.5 percent and cuts 0.1 seconds off the 0 to 60 mph time. That gives you a hint about what to expect from the 2015 Chevrolet Silverado 1500 pickup truck.
“The new 8L90 eight-speed is designed tougher to handle the greater power of the Silverado’s powertrains, with great improvements in spin loss to complement that capability with greater efficiency,” explains Kavoos Kaveh, global chief engineer for eight-speed automatic gearboxes. “It is a marvel of packaging efficiency and driving efficiency that has garnered more than two dozen patents for General Motors.” In total, the new transmission uses four gearsets, two brake clutches and three rotating clutches.
Compared to the Hydra-Matic 6L80 six-speed gearbox, the new 8L90 eight-speed automatic boasts with smaller steps between gears to keep the motor within the sweet spot of the rpm band. Lower rear axle ratios reduce engine rpm when driving on the highway, thus improving fuel economy. Compared to the 6L80's 4.03 ratio first gear, the 8L90's first gear has a 4.56 ratio. This change improves power delivery and acceleration off the line. A new torque converter design with turbine damper enhances refinement during low-speed gear changes, providing smoother performance when the truck is pulling a trailer.
Built at General Motors' transmission factory in Toledo, Ohio, the 8L90 eight-speed auto executes hundreds of commands every 6.25 milliseconds. An off-axis, chain-driven binary vane-type pump located within the valve body is also on the menu. In addition to that, clutch compensators are fed by lubrication oil rather than the dedicated and regulated feed design of the Hydra-Matic 6L80 six-speed transmission. The new design boasts with two main benefits: reduction of one oil channel between the valve body and the rotating clutches (which reduces the number of rotating oil seals and oil channels within the turbine shaft) and the capability for rapidly discharging oil in the compensators during clutch apply.
“The new 8L90 eight-speed is designed tougher to handle the greater power of the Silverado’s powertrains, with great improvements in spin loss to complement that capability with greater efficiency,” explains Kavoos Kaveh, global chief engineer for eight-speed automatic gearboxes. “It is a marvel of packaging efficiency and driving efficiency that has garnered more than two dozen patents for General Motors.” In total, the new transmission uses four gearsets, two brake clutches and three rotating clutches.
Compared to the Hydra-Matic 6L80 six-speed gearbox, the new 8L90 eight-speed automatic boasts with smaller steps between gears to keep the motor within the sweet spot of the rpm band. Lower rear axle ratios reduce engine rpm when driving on the highway, thus improving fuel economy. Compared to the 6L80's 4.03 ratio first gear, the 8L90's first gear has a 4.56 ratio. This change improves power delivery and acceleration off the line. A new torque converter design with turbine damper enhances refinement during low-speed gear changes, providing smoother performance when the truck is pulling a trailer.
Built at General Motors' transmission factory in Toledo, Ohio, the 8L90 eight-speed auto executes hundreds of commands every 6.25 milliseconds. An off-axis, chain-driven binary vane-type pump located within the valve body is also on the menu. In addition to that, clutch compensators are fed by lubrication oil rather than the dedicated and regulated feed design of the Hydra-Matic 6L80 six-speed transmission. The new design boasts with two main benefits: reduction of one oil channel between the valve body and the rotating clutches (which reduces the number of rotating oil seals and oil channels within the turbine shaft) and the capability for rapidly discharging oil in the compensators during clutch apply.
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