GM 8L transmission explained

8L 45 · 8L 90
Production:	2014–
Manufacturer:	General Motors
Class:	8-speed longitudinal automatic transmission
Predecessor:	6L 45 · 6L 50 · 6L 80 · 6L 90
Successor:	10L 80 · 10L 90 · 10L 1000
Related:	ZF 8HP

The Hydramatic 8L 45 is an eight-speed automatic transmission built by General Motors debuting in the 2016 Cadillac CT6. It is designed for use in longitudinal engine applications attached to the front-located engine^[1] with a standard bell housing. It is a hydraulic (hydramatic) design sharing much with the 8L 90 transmission.^[2] Estimated weight savings over the heavier duty 8L 90 is 33lb. Gear ratios used enable a wide 7.0 ratio spread.

The 8L 90 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 8L 45.

Both gearboxes are based on the layout of the ZF 8HP transmission from 2008, with the only difference being that gearsets 1 and 3 are swapped.^[3]

Specifications

Features!!8L 45 M5N^[5] !8L 90 M5U · N8X^[6]

Colspan=3	Input Capacity
Maximum engine power	308bhp	420bhp
Maximum gearbox torque	550Nm	900Nm
Maximum shift speed	7,500/min	6,000/min
Vehicle
Maximum Validated Weight Gross Vehicle Weight · GVW	-	-
Maximum Validated Weight Gross Curb Vehicle Weight · GCVW	12000lb	22500lb
Structure
Range-selector quadrant	P · R · N · D · M · L
Case description	2-piece main, bell integrated with main
Case material	Die cast aluminum
Shift pattern (2)	2 on/off solenoids
Shift quality	6 Variable Force Solenoids · 1 for each clutch · 1 for TCC
Torque converter clutch	Variable Force Solenoid ECCC · 2 path · turbine damper
Converter size	238mm	258mm
Fluid type	DEXRON High Performance ATF
Fluid capacity	10.8l	10.3l
Weight	80kg (180lb)	98.9kg (218lb)
Available Control Features
Shift Patterns	Multiple (Selectable)
Driver Shift Control	Tap Up and Down
Additional Modes	Tow & Haul Mode (Selectable)
Engine Torque Management	On All Shifts
Shift Control	Automatic Start/Stop Automatic Grade Braking
Assembly sites	GMPT Toledo · Ohio · USA GMPT Silao · Mexico

With Assessment! colspan="4"

Planetary Gearset: Teeth	Count	Total	Avg.
Model Type	Max. Input Torque First Delivery		S1 R1	S2 R2	S3 R3	S4 R4	Brakes Clutches	Ratio Span	Gear Step
Gear Ratio	R {i _{R}}	1 {i _{1}}	2 {i _{2}}	3 {i _{3}}	4 {i _{4}}	5 {i _{5}}	6 {i _{6}}	7 {i _{7}}	8 {i _{8}}
Step	- \tfrac{i _{R}} {i _{1}}	\tfrac{i _{1}} {i _{1}}	\tfrac{i _{1}} {i _{2}}	\tfrac{i _{2}} {i _{3}}	\tfrac{i _{3}} {i _{4}}	\tfrac{i _{4}} {i _{5}}	\tfrac{i _{5}} {i _{6}}	\tfrac{i _{6}} {i _{7}}	\tfrac{i _{7}} {i _{8}}
Step 2			\tfrac{i _{1}} {i _{2}} : \tfrac{i _{2}} {i _{3}}	\tfrac{i _{2}} {i _{3}} : \tfrac{i _{3}} {i _{4}}	\tfrac{i _{3}} {i _{4}} : \tfrac{i _{4}} {i _{5}}	\tfrac{i _{4}} {i _{5}} : \tfrac{i _{5}} {i _{6}}	\tfrac{i _{5}} {i _{6}} : \tfrac{i _{6}} {i _{7}}	\tfrac{i _{6}} {i _{7}} : \tfrac{i _{7}} {i _{8}}
Shaft Speed	\tfrac{i _{1}} {i _{R}}	\tfrac{i _{1}} {i _{1}}	\tfrac{i _{1}} {i _{2}}	\tfrac{i _{1}} {i _{3}}	\tfrac{i _{1}} {i _{4}}	\tfrac{i _{1}} {i _{5}}	\tfrac{i _{1}} {i _{6}}	\tfrac{i _{1}} {i _{7}}	\tfrac{i _{1}} {i _{8}}
Δ Shaft Speed	0 - \tfrac{i _{1}} {i _{R}}	\tfrac{i _{1}} {i _{1}} - 0	\tfrac{i _{1}} {i _{2}} - \tfrac{i _{1}} {i _{1}}	\tfrac{i _{1}} {i _{3}} - \tfrac{i _{1}} {i _{2}}	\tfrac{i _{1}} {i _{4}} - \tfrac{i _{1}} {i _{3}}	\tfrac{i _{1}} {i _{5}} - \tfrac{i _{1}} {i _{4}}	\tfrac{i _{1}} {i _{6}} - \tfrac{i _{1}} {i _{5}}	\tfrac{i _{1}} {i _{7}} - \tfrac{i _{1}} {i _{6}}	\tfrac{i _{1}} {i _{8}} - \tfrac{i _{1}} {i _{7}}
8L 45 M5N	550Nm 2015		41 79	41 79	41 79	26 94	2 3
Gear Ratio		\tfrac{ 60 }{ 13 }		\tfrac{ 7 , 200 }{ 3 , 487 }			\tfrac{ 1 }{ 1 }		\tfrac{ 79 }{ 120 }
Step		1.0000		1.4715			1.2587		1.2902
Step 2				1.1819			1.0691
Speed	–1.1751	1.0000	1.5190	2.2353		3.6669	4.6154		7.0107
Δ Speed	1.1751	1.0000	0.5190	0.7163		0.8837	0.9485		1.5769
8L 90 M5U	900Nm^[7] 2014		41^[8] 79	46 86	37 73	25 89	2 3
Gear Ratio		\tfrac{ 114 }{ 25 }		\tfrac{ 12 , 540 }{ 6 , 043 }			\tfrac{ 1 }{ 1 }		\tfrac{ 43 }{ 66 }
Step		1.0000		1.4317			1.2700		1.2977
Step 2				1.1643			1.0738
Speed	–1.1945	1.0000	1.5349	2.1975		3.5905	4.56		6.9991
Δ Speed	1.1945	1.0000	0.5349	0.6626		0.8884	0.9695		1.6057
Ratio R & even	i _{R} = \tfrac{R _{2} (S _{1} S _{4-} R _{1} R _{4)}} {S _{1} S _{4} (S _{2+} R _{2)}}		i _{2} = \tfrac{R _{2} (S _{4+} R _{4)}} {(S _{2+} R _{2)} S _{4}}		i _{4} = 1+ \tfrac{S _{2} R _{3}} {S _{3} (S _{2+} R _{2)}}		i _{6} = \tfrac{ 1 } { 1 }	i _{8} = \tfrac{R _{2}} {S _{2} + R _{2}}
Ratio odd	i _{1} = \tfrac{S _{4+} R _{4}} {S _{4}}		\tfrac{(S _{3+} R _{3)} (S _{4+} R _{4)}} {S _{4} R _{3+} S _{3} (S _{4+} R _{4)}}		\tfrac{S _{3} R _{2} R _{4} (S _{1+} R _{1)+} S _{2} S _{1} (S _{3+} R _{3)} (S _{4+} R _{4)}} {S _{3} R _{4} (S _{1} (S _{2+} R _{2)+} R _{1} R _{2)+} S _{1} S _{2} S _{4} (S _{3+} R _{3)}}			\tfrac{R _{2} (S _{1+} R _{1)}} {R _{2} (S _{1+} R _{1)+} S _{1} S _{2}}
Algebra And Actuated Shift Elements
Brake A	❶	❶	❶					❶	❶
Brake B	❶	❶	❶	❶	❶	❶
Clutch C		❶		❶		❶	❶	❶
Clutch D	❶				❶	❶	❶	❶	❶
Clutch E			❶	❶	❶		❶		❶
8HP 70	700Nm 2008		48^[9] 96	48 96	69^[10] 111	23 85	2 3
Gear Ratio		\tfrac{ 108 }{ 23 }		\tfrac{ 162 }{ 77 }			\tfrac{ 1 }{ 1 }		\tfrac{ 2 }{ 3 }
Step		1.0000		1.4879			1.2845		1.2587
Step 2				1.1787			1.0779
Speed	–1.4243	1.0000	1.5000	2.2319		3.6555	4.6957		7.0435
Δ Speed	1.4243	1.0000	0.5000	0.7319		0.8382	1.0401		1.4478
Ratio R & even	i _{R} = \tfrac{R _{2} (S _{3} S _{4-} R _{3} R _{4)}} {S _{3} S _{4} (S _{2+} R _{2)}}		i _{2} = \tfrac{R _{2} (S _{4+} R _{4)}} {(S _{2+} R _{2)} S _{4}}		i _{4} = 1+ \tfrac{S _{2} R _{1}} {S _{1} (S _{2+} R _{2)}}		i _{6} = \tfrac{ 1 } { 1 }	i _{8} = \tfrac{R _{2}} {S _{2} + R _{2}}
Ratio odd	i _{1} = \tfrac{S _{4+} R _{4}} {S _{4}}		\tfrac{(S _{1+} R _{1)} (S _{4+} R _{4)}} {S _{4} R _{1+} S _{1} (S _{4+} R _{4)}}		\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)}}			\tfrac{R _{2} (S _{3+} R _{3)}} {R _{2} (S _{3+} R _{3)+} S _{2} S _{3}}

Applications

8L 45!Make!Model Years!Model!Final Drive Ratio

Cadillac	2016–2019	ATS
	2016–2019	CTS
	2020–present	CT4
	2016–present	CT6
Chevrolet	2016–2019	Camaro
	2017–present	Colorado
GMC	2017–present	Canyon

8L 90!Make!Model Years!Model!Final Drive Ratio

Cadillac	2015–2017	Escalade^[11]	3.23
	2016–present	ATS-V	2.85
	2016–present	CTS-V	2.85
	2016–present	CT6	3.27
Chevrolet	2015–2019	Corvette (C7) Stingray^[12]	2.41 or 2.73
	2015–2019	Corvette (C7) Z06^[13]	2.41
	2019	Corvette (C7) ZR1	2.73
	2015–present	Silverado^[14]	3.23 or 3.42
	2015–present	Colorado	3.42
	2016–2018	Camaro SS	2.77
	2017–present	Express
GMC	2015–2017	Yukon Denali · Denali XL	3.23
	2015–present	Sierra	3.23
	2015–present	Canyon	3.42
	2017–present	Savana

Lawsuits

The 8L 90 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.^[15]

See also

• List of GM transmissions

External links

• General Motors Powertrain Division
• https://gmauthority.com/blog/gm/gm-transmissions/m5n/
• https://gmauthority.com/blog/gm/gm-transmissions/m5u/

Notes and References

1. Web site: USA Information Guide Model Year 2018. 15 July 2019.
2. Web site: Cadillac Introduces New 8-Speed Automatic on CT6. Cadillac Media USA. 20 March 2015 . Cadillac Media USA. 20 March 2015.
3. Web site: Timur Apakidze · Saturation Dive: The GM 8L 90 8-Speed Transmission . TTAC: The Truth About Cars . 23 April 2014 . 12 April 2024.
4. Web site: New 8-Speed Enables Quicker, More Efficient Corvette . www.gm.com . General Motors . 21 August 2014 . 20 August 2014 . dead . https://web.archive.org/web/20141222140302/http://www.gm.com/article.content_pages_news_us_en_2014_aug_0820-8speed_0820-corvette-8-speed-lead.html . 22 December 2014 .
5. https://poweredsolutions.gm.com/products/8l45-8-speed-transmission/
6. https://poweredsolutions.gm.com/products/8l90-8-speed-transmission/
7. Web site: Transmission Repair Cost Guide. 15 July 2019.
8. Web site: WIT · Whatever It Takes · Automatic Transmission Parts Catalog 2018+2019 Page 268. 15 July 2019.
9. 8HP 70 Repair Manual · Picture 10106 p. 110 · Saarbruecken 2014 · https://avtgr.ru/upload/data/pdf/zf_instructions/8HP70.pdf
10. Web site: Timur Apakidze · Saturation Dive: ZF 8-Speed Automatic. TTAC: The Truth About Cars . 11 March 2014 . 7 July 2019.
11. Web site: 2015 Cadillac Escalade Updated with 8L90 8-Speed Automatic and More Tech [Photo Gallery]]. 11 August 2014 . 12 August 2014.
12. Web site: Chevrolet Confirms 2015 Corvette Stingray To Utilize 8L90 Eight-Speed Gearbox. 9 April 2014.
13. Web site: Supercharged 2015 Chevy Corvette Z06 takes the C7 beyond the ZR1 [w/video]]. 25 January 2014.
14. Web site: GM confirms 2015 Silverado, Sierra to get 8-speed automatic. 18 June 2014.
15. Web site: Class Action Lawsuit Filed Over Alleged Shifting Defect in Certain General Motors Transmissions. 19 December 2018 . 2 February 2019.