GM 8L transmission

8L 45 · 8L 90
Overview
Manufacturer	General Motors
Production	2014–
Body and chassis
Class	8-speed longitudinal automatic transmission
Related	ZF 8HP · Aisin-Toyota 8-speed · MB 9G-Tronic
Chronology
Predecessor	6L 45 · 6L 50 · 6L 80 · 6L 90
Successor	10L 80 · 10L 90 · 10L 1000

All 8L transmissions are based on the same globally patented gearset concept as the ZF 8HP from 2008. While fully retaining the same gearset logic, they differ from this only in the patented arrangement of the components with gearsets 1 and 3 swapped.

The 8L 90 is the first 8-speed automatic transmission built by General Motors. It was debuting in 2014 and is designed for use in longitudinal engine applications either attached to the front-located engine 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.

The 8L 45 is the smaller variant and was debuting in 2015 in the 2016 Cadillac CT6. It is designed for use in longitudinal engine applications attached to the front-located engine with a standard bell housing. It is a hydraulic (hydramatic) design sharing much with the 8L 90 transmission. Estimated weight savings over the heavier duty 8L 90 is 33 lb (15 kg).

The ZF 8HP became the new benchmark for automatic transmissions.

Gear Ratios

Gear Model	R	1	2	3	4	5	6	7	8	Total Span	Span Center	Avg. Step	Compo- nents
8L 90 · M5U · 2014	−3.818	4.560	2.971	2.075	1.688	1.270	1.000	0.845	0.652	6.999	1.724	1.320	4 Gearsets 2 Brakes 3 Clutches
8L 45 · M5N · 2015	−3.928	4.615	3.038	2.065	1.658	1.259	1.000	0.849	0.658	7.011	1.743	1.321
ZF 8HP 70 · 2008	−3.297	4.696	3.130	2.104	1.667	1.285	1.000	0.839	0.667	7.043	1.769	1.322

Specifications

Features

	8L 45 M5N	8L 90 M5U · N8X
Input Capacity
Maximum engine power	308 bhp (230 kW)	420 bhp (313 kW)
Maximum gearbox torque	550 N⋅m (406 lb⋅ft)	900 N⋅m (664 lb⋅ft)
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	12,000 lb (5,440 kg)	22,500 lb (10,210 kg)
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	238 mm (9.37 in)	258 mm (10.16 in)
Fluid type	DEXRON High Performance ATF
Fluid capacity	10.8 L (11.4 US qt)	10.3 L (10.9 US qt)
Weight	80 kg (176 lb)	98.9 kg (218 lb)
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

Layout (Gearset Concept) Progress

The main objective in replacing the predecessor model was to improve vehicle fuel economy with extra speeds and a wider gear span to allow the engine speed level to be lowered (downspeeding). The layout brings the ability to shift in a non-sequential manner – going from gear 8 to gear 2 in extreme situations simply by changing one shift element (actuating break B and releasing clutch D).

Progress Quality

In order to increase the number of ratios, ZF and consequently GM have abandoned the conventional design method of limiting themselves to pure in-line epicyclic gearing and extended it to a combination with parallel epicyclic gearing. This was only possible thanks to computer-aided design and has resulted in a globally patented gearset concept. The resulting progress is reflected in a better ratio of the number of gears to the number of components used compared to existing layouts. The ZF 8HP has become the new reference standard (benchmark) for automatic transmissions.

Innovative Strength Analysis

With Asessment	Output: Gear Ratios	Innovation Elasticity Δ Output : Δ Input	Input: Main Components
			Total	Gearsets	Brakes	Clutches
8L Ref. Object	$n_{O1}$ $n_{O2}$	Topic	$n_{I}=n_{G}+$ $n_{B}+n_{C}$	$n_{G1}$ $n_{G2}$	$n_{B1}$ $n_{B2}$	$n_{C1}$ $n_{C2}$
Δ Number	$n_{O1}-n_{O2}$		Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "http://localhost:6011/wiki.riteme.site/v1/":): {\displaystyle n_{I1}- n_{I2}}	$n_{G1}-n_{G2}$	$n_{B1}-n_{B2}$	$n_{C1}-n_{C2}$
Relative Δ	Δ Output ${\tfrac {n_{O1}-n_{O2}}{n_{O2}}}$	${\tfrac {n_{O1}-n_{O2}}{n_{O2}}}:{\tfrac {n_{I1}-n_{I2}}{n_{I2}}}$ $={\tfrac {n_{O1}-n_{O2}}{n_{O2}}}$·${\tfrac {n_{I2}}{n_{I1}-n_{I2}}}$	Δ Input ${\tfrac {n_{I1}-n_{I2}}{n_{I2}}}$	${\tfrac {n_{G1}-n_{G2}}{n_{G2}}}$	${\tfrac {n_{B1}-n_{B2}}{n_{B2}}}$	${\tfrac {n_{C1}-n_{C2}}{n_{C2}}}$
8L 6L	8 6	Progress	9 8	4 3	2 2	3 3
Δ Number	2		1	1	0	0
Relative Δ	0.333 ${\tfrac {1}{3}}$	2.667 ${\tfrac {1}{3}}:{\tfrac {1}{8}}={\tfrac {1}{3}}$·${\tfrac {8}{1}}={\tfrac {8}{3}}$	0.125 ${\tfrac {1}{8}}$	0.333 ${\tfrac {1}{3}}$	0.000 ${\tfrac {0}{2}}$	0.000 ${\tfrac {0}{3}}$
8L 3-Speed	8 3	Market Position	9 7	4 2	2 3	3 2
Δ Number	5		2	2	-1	1
Relative Δ	1.667 ${\tfrac {5}{3}}$	5.833 ${\tfrac {5}{3}}:{\tfrac {2}{7}}={\tfrac {5}{3}}$·${\tfrac {7}{2}}={\tfrac {35}{6}}$	0.286 ${\tfrac {2}{7}}$	1.000 ${\tfrac {1}{1}}$	−0.333 ${\tfrac {-1}{3}}$	0.500 ${\tfrac {1}{2}}$

Layout Quality

The ratios of the 8 gears are relatively unevenly distributed in all versions. Particularly noticeable are the too small step between 3rd and 4th gear and the too large one between 7th and 8th gear. This cannot be eliminated without affecting all other gear ratios. On the other hand the selected gearset concept offers 2 to 3 gears more than conventional transmissions of comparable manufacturing costs, which more than compensates for the weaknesses.

Gear Ratio Analysis

With Assessment			Planetary Gearset: Teeth				Count	Total Center	Avg.
Model Type	Version 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	$-{\tfrac {i_{R}}{i_{1}}}$	${\tfrac {i_{1}}{i_{1}}}$	${\tfrac {i_{1}}{i_{2}}}$	${\tfrac {i_{2}}{i_{3}}}$	${\tfrac {i_{3}}{i_{4}}}$	${\tfrac {i_{4}}{i_{5}}}$	${\tfrac {i_{5}}{i_{6}}}$	${\tfrac {i_{6}}{i_{7}}}$	${\tfrac {i_{7}}{i_{8}}}$
Δ Step			${\tfrac {i_{1}}{i_{2}}}:{\tfrac {i_{2}}{i_{3}}}$	${\tfrac {i_{2}}{i_{3}}}:{\tfrac {i_{3}}{i_{4}}}$	${\tfrac {i_{3}}{i_{4}}}:{\tfrac {i_{4}}{i_{5}}}$	${\tfrac {i_{4}}{i_{5}}}:{\tfrac {i_{5}}{i_{6}}}$	${\tfrac {i_{5}}{i_{6}}}:{\tfrac {i_{6}}{i_{7}}}$	${\tfrac {i_{6}}{i_{7}}}:{\tfrac {i_{7}}{i_{8}}}$
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 90 M5U	900 N⋅m (664 lb⋅ft) 2014		41 79	46 86	37 73	25 89	2 3	6.9991 1.7236	1.3204
Gear Ratio	−3.8176 $-{\tfrac {43,043}{11,275}}$	4.5600 ${\tfrac {114}{25}}$	2.9709 ${\tfrac {817}{275}}$	2.0751 ${\tfrac {12,540}{6,043}}$	1.6876 ${\tfrac {4,121}{2,442}}$	1.2700 ${\tfrac {28,817,100}{22,690,429}}$	1.0000 ${\tfrac {1}{1}}$	0.8455 ${\tfrac {5,160}{6,103}}$	0.6515 ${\tfrac {43}{66}}$
Step	0.8372	1.0000	1.5349	1.4317	1.2297	1.3288	1.2700	1.1828	1.2977
Δ Step			1.0721	1.1643	0.9254	1.0463	1.0738	0.9114
Speed	-1.1945	1.0000	1.5349	2.1975	2.7021	3.5905	4.56	5.3933	6.9991
Δ Speed	1.1945	1.0000	0.5349	0.6626	0.5047	0.8884	0.9695	0.8333	1.6057
8L 45 M5N	550 N⋅m (406 lb⋅ft) 2015		41 79	41 79	41 79	26 94	2 3	7.0107 1.7431	1.3208
Gear Ratio	−3.9278 $-{\tfrac {4,187}{1,066}}$	4.6154 ${\tfrac {60}{13}}$	3.0385 ${\tfrac {79}{26}}$	2.0648 ${\tfrac {7,200}{3,487}}$	1.6583 ${\tfrac {199}{120}}$	1.2587 ${\tfrac {740,760}{588,527}}$	1.0000 ${\tfrac {1}{1}}$	0.8494 ${\tfrac {9,480}{11,161}}$	0.6583 ${\tfrac {79}{120}}$
Step	0.8510	1.0000	1.5190	1.4715	1.2451	1.3175	1.2587	1.1773	1.2902
Δ Step			1.0322	1.1819	0.9450	1.0468	1.0691	0.9125
Speed	-1.1751	1.0000	1.5190	2.2353	2.7831	3.6669	4.6154	5.4338	7.0107
Δ Speed	1.1751	1.0000	0.5190	0.7163	0.5479	0.8837	0.9485	0.8184	1.5769
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	700 N⋅m (516 lb⋅ft) 2008		48 96	48 96	69 111	23 85	2 3	7.0435 1.7693	1.3216
Gear Ratio	−3.2968 $-{\tfrac {1,744}{529}}$	4.6957 ${\tfrac {108}{23}}$	3.1304 ${\tfrac {72}{23}}$	2.1039 ${\tfrac {162}{77}}$	1.6667 ${\tfrac {5}{3}}$	1.2845 ${\tfrac {8,826}{6,871}}$	1.0000 ${\tfrac {1}{1}}$	0.8392 ${\tfrac {120}{143}}$	0.6667 ${\tfrac {2}{3}}$
Step	0.7021	1.0000	1.5000	1.4879	1.2623	1.2975	1.2845	1.1917	1.2587
Δ Step			1.0081	1.1787	0.9729	1.0101	1.0779	0.9467
Speed	-1.4243	1.0000	1.5000	2.2319	2.8174	3.6555	4.6957	5.5965	7.0435
Δ Speed	1.4243	1.0000	0.5000	0.7319	0.5855	0.8382	1.0401	0.9000	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 90

Make	Model Years	Model	Final Drive Ratio
Cadillac	2015–2017	Escalade	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	2.41 or 2.73
	2015–2019	Corvette (C7) Z06	2.41
	2019	Corvette (C7) ZR1	2.73
	2015–present	Silverado	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

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	3.27 or 2.77
	2017–present	Colorado	3.42
GMC	2017–present	Canyon

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.

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/