The 8L90 is an eight-speed automatic transmission built by General Motors. It is designed for use in longitudinal engine applications either attached to the front-located engine^[1] with a standard bell housing or in the rear of the car adjacent to the differential (as in the Corvette). It is a hydraulic (hydramatic) design. GM also produces a similar design with the smaller 8L45.

The 8L90 is the subject of a class-action lawsuit filed in December 2018 that alleges the transmission suffers from persistent "shudder" issues and that GM has known about the problems since its introduction and has failed to provide a solution, instead choosing to wait until the unit is out of warranty.^[2]

Specifications

Gear Teeth and Ratios[3]			Planetary Gearset: Teeth				Count	Total	Avg.
Model Type	Version First Delivery		Sun 1 ${\displaystyle {S_{1}}}$ Ring 1 ${\displaystyle {R_{1}}}$	Sun 2 ${\displaystyle {S_{2}}}$ Ring 2 ${\displaystyle {R_{2}}}$	Sun 3 ${\displaystyle {S_{3}}}$ Ring 3 ${\displaystyle {R_{3}}}$	Sun 4 ${\displaystyle {S_{4}}}$ Ring 4 ${\displaystyle {R_{4}}}$	Brakes Clutches	Ratio Span	Gear Step
Gear	R	1	2	3	4	5	6	7	8
8L90 M5U	900 N⋅m (664 lb⋅ft)[4] 2014		41[5] 79	46 86	37 73	25 89	2 3	6.9991	1.3204
Ratio	–3.8176	4.5600	2.9709	2.0751	1.6876	1.2700	1.0000	0.8455	0.6515
8L45 M5T	550 N⋅m (406 lb⋅ft) 2015		41 79	41 79	41 79	26 94	2 3	7.0107	1.3208
Ratio	–3.9278	4.6154	3.0385	2.0648	1.6583	1.2587	1.0000	0.8494	0.6583
Ratio R & even	${\displaystyle {\tfrac {R_{2}(S_{3}S_{4}-R_{3}R_{4})}{S_{3}S_{4}(S_{2}+R_{2})}}}$		${\displaystyle {\tfrac {R_{2}(S_{4}+R_{4})}{(S_{2}+R_{2})S_{4}}}}$		${\displaystyle 1+{\tfrac {S_{2}R_{1}}{S_{1}(S_{2}+R_{2})}}}$		${\displaystyle {\tfrac {1}{1}}}$		${\displaystyle {\tfrac {R_{2}}{S_{2}+R_{2}}}}$
Ratio odd		${\displaystyle {\tfrac {S_{4}+R_{4}}{S_{4}}}}$	${\displaystyle {\tfrac {(S_{1}+R_{1})(S_{4}+R_{4})}{S_{4}R_{1}+S_{1}(S_{4}+R_{4})}}}$		${\displaystyle {\tfrac {S_{1}R_{2}R_{4}(S_{3}+R_{3})+S_{2}S_{3}(S_{1}+R_{1})(S_{4}+R_{4})}{S_{1}R_{4}(S_{3}(S_{2}+R_{2})+R_{2}R_{3})+S_{2}S_{3}S_{4}(S_{1}+R_{1})}}}$			${\displaystyle {\tfrac {R_{2}(S_{3}+R_{3})}{R_{2}(S_{3}+R_{3})+S_{2}S_{3}}}}$

Applications

References

External links

• General Motors Powertrain Division