GM 8-Speed 8L90 M5U Hydra-Matic Automatic Transmission
The Hydra-Matic 8L90 (production code M5U) is a fuel-saving and electronically controlled eight-speed automatic transmission developed and produced by General Motors for use in rear- and rear-biased all-wheel-drive vehicles with a longitudinal powertrain orientation. Used in full-size trucks, SUVs, sports cars, and luxury cars, the Hydra-Matic 8L90 is part of the 8LXX family of transmissions that succeeded the 6LXX family.
Designed and built by GM, the 8L90 transmission speed is expected to contribute up to 5-percent greater efficiency, when compared to the previous 6L90 six-speed automatic. Smaller steps between gears, compared to the Hydra-Matic 6L90 six-speed automatic, keep the engine within the sweet spot of the rpm band, making the most of its horsepower and torque to optimize performance and efficiency.
For performance driving in the Corvette, the transmission offers full manual control via steering wheel paddles, and unique algorithms to deliver shift performance that rivals the dual-clutch/semi-automatic transmissions found in many supercars – but with the smoothness and refinement that comes with a conventional automatic fitted with a torque converter.
The 8L90 has a torque capacity of 738 pound-feet (1000 Nm).
Compact And Lightweight
Featuring four gearsets and five clutches, creative packaging enables the 8L90 to fit the same space as the previous 6L80/6L90 family of six-speed automatics. Extensive use of aluminum and even magnesium also make it more than eight pounds (4 kg) lighter than the six-speed (in Corvette applications). Along with design features that reduce friction, the 8L90 is expected to contribute up to 5-percent greater efficiency, when compared with a six-speed automatic.
Five clutches are used, three at a time, leaving only two open clutches in each gear state. Optimized clutch sizing and off axis binary pump contribute to outstanding spinloss attributes.
All applications feature adaptive shift controls. Several features such as grade braking, Performance Algorithm Shifting, and Driver Shift Control are available on some of the applications. Performance Algorithm Shifting (PAS) monitors how assertively the driver is using engine output and other vehicle sensors to determine at what engine speed to upshift of downshift. Driver Shift Control allows the driver to shift the transmission like a clutchless manual gearbox. Electronic safeguards prevent over-revving if the wrong gear position is selected.
The 8L90 uses VFS control components to monitor clutch pressures with optimum accuracy. The result are faster and more precise shifts.
The 8L90’s 32-bit transmission control module (TCM) monitors transmission performance and compensates for normal wear in components such as clutch plates, so performance is consistent for the life of the transmission. The control module also “tests” the components to optimize their interaction on an on-going basis.
The 8L90’s controller analyzes and executes commands,the processor microcontroller executes instruction at a rate of 120 Million Instructions per second, and wide-open-throttle upshifts are executed up to eight-hundredths of a second quicker than those of the dual-clutch transmission offered in the Porsche 911.
The torque converter is 258 mm in diameter and features a lock-up clutch, although clutch and converter specifications vary depending on the application. The 8L90 uses electronic controlled capacity clutch (ECCC) technology, which employs a small, regulated amount of slip to dampen out engine pulses for a smoother running drivetrain, especially during shifting.
The 8L90 uses Dex 6 HP Transmission fluid, which was developed to have a more consistent viscosity profile as well as improved lubrication characteristics.
|Type:||Eight speed RWD / AWD, electronically controlled automatic overdrive transmission with torque converter clutch. Clutch-to-clutch architecture, with external transmission control module|
|Maximum engine power:||650 hp (485 kW)|
|Maximum engine torque:||635 lb-ft (860 Nm)|
|Maximum gearbox torque:||738 lb-ft (1000 Nm)|
|Maximum shift speed:||7000 rpm|
|Maximum Vehicle Weight (GVW):||13,200 lbs (6,000 kg)|
|Maximum Vehicle Weight (GCVW):||20,500 lbs (9300 kg)|
|Range selector quadrants:||5 position (P,R,N,D,M) protected for 6 position (P,R,N,D,M,L)|
|Case description:||2-piece (main, extension, bell integrated with main case)|
|Case material:||Die cast aluminum|
|Shift pattern:||6 variable force solenoids, one for each clutch and one for TCC|
|Shift quality:||6 variable force solenoids, one for each clutch and one for TCC|
|Torque converter clutch:||Variable Force Solenoid ECCC, 2 path, turbine damper|
|Converter size:||258 mm|
|Fluid type:||Dexron High Performance ATF|
|Fluid capacity (application specific):||10.5 L|
|Transmission weight (application specific):||95.5 kg – 99 kg, including TCM|
|Pressure taps available:||c12345R Clutch|
|Assembly site:||Toledo, Ohio, USA|
|Available Control Features|
|Multiple Shift Patterns (Selectable)|
|Driver Shift Control (Tap Up / Tap Down)|
|Enhanced Performance Algorithm Shifting (PAS/PAL)|
|Engine Rev Matching on TAP Downshifts|
|Staged Upshifts in TAP Mode|
|Selectable Tow / Haul Mode (Truck Only)|
|Engine Torque Management On All Shifts|
|Altitude and Temperature Compensation|
|Adaptive Shift Time|
|Automatic Grade Braking|
|Control Interface Protocol – GMLAN|
|Chevrolet Silverado (Double Cab, Crew)||6.2L V8 L86 NA|
|Chevrolet Corvette Z06 (Coupe, Convertible)||6.2L V8 LT4 Supercharged|
|Chevrolet Corvette, Corvette Z51 Coupe||6.2L V8 LT1 NA|
|Cadillac Escalade, Escalade ESV||6.2L V8 L86 NA|
|GMC Sierra (Double Cab, Crew)||6.2L V8 L86 NA|
|GMC Yukon Denali, Yukon XL Denali||6.2L V8 L86 NA|