GM 8L transmission

8L 45 · 8L 90
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

The Hydramatic 8L 45 is an 8-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 33 lb (15 kg). Gear ratios used enable a wide 7.0 ratio spread.

The 8L 90 is an 8-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.

Gear Ratios^[a]^[3]
Gear Model	R	1	2	3	4	5	6	7	8	Total Span	Span Center	Avg. Step	Compo- nents

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	4 Gearsets 2 Brakes 3 Clutches
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

ZF 8HP 70 · 2008^[b]	−3.297	4.696	3.130	2.104	1.667	1.285	1.000	0.839	0.667	7.043	1.769	1.322

^ Differences in gear ratios have a measurable, direct impact on vehicle dynamics, performance, waste emissions as well as fuel mileage
^ for comparison purposes only

Specifications

Both gearboxes are based on the layout of the ZF 8HP transmission from 2008, with the gearsets 1 and 3 swapped.^[4]

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

Input Capacity
Maximum engine power	308 bhp (230 kW)^[a]	420 bhp (313 kW)^[b]
Maximum gearbox torque	550 N⋅m (406 lb⋅ft)^[a]	900 N⋅m (664 lb⋅ft)^[b]
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)^[a]	22,500 lb (10,210 kg)^[b]
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)^[a]	10.3 L (10.9 US qt)^[b]
Weight	80 kg (176 lb)^[a]	98.9 kg (218 lb)^[b]
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^[c] Toledo · Ohio · USA GMPT^[c] Silao · Mexico

^ ^a ^b ^c ^d ^e based on 2020 Chevrolet Colorado Z71 2WD Crew Cab · Short Bed ^ ^a ^b ^c ^d ^e General Motors estimate ^ ^a ^b General Motors Powertrain

Gear Ratios
With Assessment			Planetary Gearset: Teeth^[a]^[b]				Count	Total^[c] Center^[d]	Avg.^[e]

Model Type	Version First Delivery		S₁^[f] R₁^[g]	S₂^[h] R₂^[i]	S₃^[j] R₃^[k]	S₄^[l] R₄^[m]	Brakes Clutches	Ratio Span	Gear Step^[n]
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^[n]	$-{\tfrac {i_{R}}{i_{1}}}$ ^[o]	${\tfrac {i_{1}}{i_{1}}}$	${\tfrac {i_{1}}{i_{2}}}$ ^[p]	${\tfrac {i_{2}}{i_{3}}}$	${\tfrac {i_{3}}{i_{4}}}$	${\tfrac {i_{4}}{i_{5}}}$	${\tfrac {i_{5}}{i_{6}}}$	${\tfrac {i_{6}}{i_{7}}}$	${\tfrac {i_{7}}{i_{8}}}$
Δ Step^[q]^[r]			${\tfrac {i_{1}}{i_{2}}}:{\tfrac {i_{2}}{i_{3}}}$	${\tfrac {i_{2}}{i_{3}}}:{\tfrac {i_{3}}{i_{4}}}$	${\tfrac {i_{3}}{i_{4}}}:{\tfrac {i_{4}}{i_{5}}}$	${\tfrac {i_{4}}{i_{5}}}:{\tfrac {i_{5}}{i_{6}}}$	${\tfrac {i_{5}}{i_{6}}}:{\tfrac {i_{6}}{i_{7}}}$	${\tfrac {i_{6}}{i_{7}}}:{\tfrac {i_{7}}{i_{8}}}$
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^[s]	$0-{\tfrac {i_{1}}{i_{R}}}$	${\tfrac {i_{1}}{i_{1}}}-0$	${\tfrac {i_{1}}{i_{2}}}-{\tfrac {i_{1}}{i_{1}}}$	${\tfrac {i_{1}}{i_{3}}}-{\tfrac {i_{1}}{i_{2}}}$	${\tfrac {i_{1}}{i_{4}}}-{\tfrac {i_{1}}{i_{3}}}$	${\tfrac {i_{1}}{i_{5}}}-{\tfrac {i_{1}}{i_{4}}}$	${\tfrac {i_{1}}{i_{6}}}-{\tfrac {i_{1}}{i_{5}}}$	${\tfrac {i_{1}}{i_{7}}}-{\tfrac {i_{1}}{i_{6}}}$	${\tfrac {i_{1}}{i_{8}}}-{\tfrac {i_{1}}{i_{7}}}$

8L 45 M5N	550 N⋅m (406 lb⋅ft) 2015^[t]		41 79	41 79	41 79	26 94	2 3	7.0107 1.7431	1.3208^[n]
Gear Ratio	−3.9278^[o] $-{\tfrac {4,187}{1,066}}$	4.6154 ${\tfrac {60}{13}}$	3.0385^[r] ${\tfrac {79}{26}}$	2.0648 ${\tfrac {7,200}{3,487}}$	1.6583^[n]^[r]^[s] ${\tfrac {199}{120}}$	1.2587^[r] ${\tfrac {740,760}{588,527}}$	1.0000 ${\tfrac {1}{1}}$	0.8494^[r]^[s] ${\tfrac {9,480}{11,161}}$	0.6583 ${\tfrac {79}{120}}$
Step	0.8510^[o]	1.0000	1.5190	1.4715	1.2451^[n]	1.3175	1.2587	1.1773	1.2902
Δ Step^[q]			1.0322^[r]	1.1819	0.9450^[r]	1.0468^[r]	1.0691	0.9125^[r]
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^[s]	0.8837	0.9485	0.8184^[s]	1.5769

8L 90 M5U	900 N⋅m (664 lb⋅ft)^[7] 2014^[u]		41^[8] 79	46 86	37 73	25 89	2 3	6.9991 1.7236	1.3204^[n]
Gear Ratio	−3.8176^[o] $-{\tfrac {43,043}{11,275}}$	4.5600 ${\tfrac {114}{25}}$	2.9709^[r] ${\tfrac {817}{275}}$	2.0751 ${\tfrac {12,540}{6,043}}$	1.6876^[n]^[r]^[s] ${\tfrac {4,121}{2,442}}$	1.2700^[r] ${\tfrac {28,817,100}{22,690,429}}$	1.0000 ${\tfrac {1}{1}}$	0.8455^[r]^[s] ${\tfrac {5,160}{6,103}}$	0.6515 ${\tfrac {43}{66}}$
Step	0.8372^[o]	1.0000	1.5349	1.4317	1.2297^[n]	1.3288	1.2700	1.1828	1.2977
Δ Step^[q]			1.0721^[r]	1.1643	0.9254^[r]	1.0463^[r]	1.0738	0.9114^[r]
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^[s]	0.8884	0.9695	0.8333^[s]	1.6057

Ratio^[v] 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^[v] 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^[w]
Brake A^[x]	❶	❶	❶					❶	❶
Brake B^[y]	❶	❶	❶	❶	❶	❶
Clutch C^[z]		❶		❶		❶	❶	❶
Clutch D^[aa]	❶				❶	❶	❶	❶	❶
Clutch E^[ab]			❶	❶	❶		❶		❶

8HP 70 ^[ac]^[ad]	700 N⋅m (516 lb⋅ft) 2008		48^[9] 96	48^[9] 96	69^[10] 111	23^[10] 85	2 3	7.0435 1.7693	1.3216^[n]
Gear Ratio	−3.2968^[o] $-{\tfrac {1,744}{529}}$	4.6957 ${\tfrac {108}{23}}$	3.1304^[r] ${\tfrac {72}{23}}$	2.1039 ${\tfrac {162}{77}}$	1.6667^[n]^[r]^[s] ${\tfrac {5}{3}}$	1.2845^[r] ${\tfrac {8,826}{6,871}}$	1.0000 ${\tfrac {1}{1}}$	0.8392^[r]^[s] ${\tfrac {120}{143}}$	0.6667 ${\tfrac {2}{3}}$
Step	0.7021^[o]	1.0000	1.5000	1.4879	1.2623^[n]	1.2975	1.2845	1.1917	1.2587
Δ Step^[q]			1.0081^[r]	1.1787	0.9729^[r]	1.0101^[r]	1.0779	0.9467^[r]
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^[s]	0.8382	1.0401	0.9000^[s]	1.4478

Ratio^[ae] 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^[ae] Odd	$i_{1}={\tfrac {S_{4}+R_{4}}{S_{4}}}$		${\tfrac {(S_{1}+R_{1})(S_{4}+R_{4})}{S_{4}R_{1}+S_{1}(S_{4}+R_{4})}}$		${\tfrac {S_{1}R_{2}R_{4}(S_{3}+R_{3})+S_{2}S_{3}(S_{1}+R_{1})(S_{4}+R_{4})}{S_{1}R_{4}(S_{3}(S_{2}+R_{2})+R_{2}R_{3})+S_{2}S_{3}S_{4}(S_{1}+R_{1})}}$			${\tfrac {R_{2}(S_{3}+R_{3})}{R_{2}(S_{3}+R_{3})+S_{2}S_{3}}}$

^ All 8L-transmissions are based on a dedicated 8-speed layout, first realized in the ZF 8HP 70 gearbox ^ Layout Input and output are on opposite sides Planetary gearset 1 is on the input (turbine) side Input shafts are C₂ and, if actuated, R₁ and S₄ Output shaft is C₄ (planetary gear carrier of gearset 4) ^ Total Ratio Span (Total Ratio Spread · Total Gear Ratio) ${\tfrac {i_{n}}{i_{1}}}$ A wider span enables the downspeeding when driving outside the city limits increase the climbing ability when driving over mountain passes or off-road or when towing a trailer ^ Ratio Span's Center $(i_{n}i_{1})^{\tfrac {1}{2}}$ The center indicates the speed level of the transmission Together with the final drive ratio it gives the shaft speed level of the vehicle ^ Average Gear Step $({\tfrac {i_{n}}{i_{1}}})^{\tfrac {1}{n-1}}$ With decreasing step width the gears connect better to each other shifting comfort increases ^ Sun 1: sun gear of gearset 1 ^ Ring 1: ring gear of gearset 1 ^ Sun 2: sun gear of gearset 2 ^ Ring 2: ring gear of gearset 2 ^ Sun 3: sun gear of gearset 3 ^ Ring 3: ring gear of gearset 3 ^ Sun 4: sun gear of gearset 4 ^ Ring 4: ring gear of gearset 4 ^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k Standard 50:50 — 50 % Is Above And 50 % Is Below The Average Gear Step — With steadily decreasing gear steps (yellow highlighted line Step) and a particularly large step from 1st to 2nd gear the lower half of the gear steps (between the small gears; rounded down, here the first 3) is always larger and the upper half of the gear steps (between the large gears; rounded up, here the last 4) is always smaller than the average gear step (cell highlighted yellow two rows above on the far right) lower half: smaller gear steps are a waste of possible ratios (red bold) upper half: larger gear steps are unsatisfactory (red bold) ^ ^a ^b ^c ^d ^e ^f ^g Standard R:1 — Reverse And 1st Gear Have The Same Ratio — The ideal reverse gear has the same transmission ratio as 1st gear no impairment when maneuvering especially when towing a trailer a torque converter can only partially compensate for this deficiency Plus 11.11 % minus 10 % compared to 1st gear is good Plus 25 % minus 20 % is acceptable (red) Above this is unsatisfactory (bold) ^ Standard 1:2 — Gear Step 1st To 2nd Gear As Small As Possible — With continuously decreasing gear steps (yellow marked line Step) the largest gear step is the one from 1st to 2nd gear, which for a good speed connection and a smooth gear shift must be as small as possible A gear ratio of up to 1.6667:1 (5:3) is good Up to 1.7500:1 (7:4) is acceptable (red) Above is unsatisfactory (bold) ^ ^a ^b ^c ^d From large to small gears (from right to left) ^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m ⁿ ^o ^p ^q ^r ^s ^t ^u ^v ^w ^x ^y Standard STEP — From Large To Small Gears: Steady And Progressive Increase In Gear Steps — Gear steps should increase: Δ Step (first green highlighted line Δ Step) is always greater than 1 As progressive as possible: Δ Step is always greater than the previous step Not progressively increasing is acceptable (red) Not increasing is unsatisfactory (bold) ^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m Standard SPEED — From Small To Large Gears: Steady Increase In Shaft Speed Difference — Shaft speed differences should increase: Δ Shaft Speed (second line marked in green Δ (Shaft) Speed) is always greater than the previous one 1 difference smaller than the previous one is acceptable (red) 2 consecutive ones are a waste of possible ratios (bold) ^ Model year 2016 ^ Model year 2015 ^ ^a ^b Adjusted formulas with gearset 1 and 3 swapped ^ Permanently coupled elements S₁ and R₂ C₁ (carrier 1) and C₄ (carrier 4) S₂ and S₃ C₃ (carrier 3) and R₄ ^ Blocks S₂ and S₃ ^ Blocks R₃ ^ Couples C₂ and S₄ with the turbine ^ Couples R₁ with S₄ ^ Couples S₁ and R₂ with S₄ ^ without generation designation ^ First transmission on the market to use the dedicated 8-speed layout gearset 1 and 3 not swapped for comparison purposes only ^ ^a ^b Original formulas gearset 1 and 3 not swapped for comparison purposes only

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	3.27^[a] or 2.77^[b]
Chevrolet	2017–present	Colorado	3.42
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^[a] or 2.73^[c]
	2015–2019	Corvette (C7) Z06^[13]	2.41
	2019	Corvette (C7) ZR1	2.73
	2015–present	Silverado^[14]	3.23^[a] or 3.42^[d]
	2015–present	Colorado	3.42
	2016–2018	Camaro SS	2.77
	2017–present	Express^[e]
GMC	2015–2017	Yukon Denali · Denali XL	3.23
	2015–present	Sierra^[14]	3.23
	2015–present	Canyon	3.42
	2017–present	Savana^[e]

^ ^a ^b ^c Standard
^ 3.6 L engine
^ Z51
^ Maximum Trailering Package
^ ^a ^b 2.8 L diesel engine and 4.3 L gas engine only

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]

References

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

External links

[3] Differences in gear ratios have a measurable, direct impact on vehicle dynamics, performance, waste emissions as well as fuel mileage

[5] r comparison purposes only

[short_bed-9] sed on 2020 Chevrolet Colorado Z71 2WD Crew Cab · Short Bed

[estimate-10] General Motors estimate

[GMPT-11] General Motors Powertrain

[12] All 8L-transmissions are based on a dedicated 8-speed layout, first realized in the ZF 8HP 70 gearbox

[13] Layout
Input and output are on opposite sides

Planetary gearset 1 is on the input (turbine) side

Input shafts are C₂ and, if actuated, R₁ and S₄

Output shaft is C₄ (planetary gear carrier of gearset 4)

[8] Input and output are on opposite sides

[9] Planetary gearset 1 is on the input (turbine) side

[10] Input shafts are C₂ and, if actuated, R₁ and S₄

[11] Output shaft is C₄ (planetary gear carrier of gearset 4)

[14] Total Ratio Span (Total Ratio Spread · Total Gear Ratio)
${\tfrac {i_{n}}{i_{1}}}$

A wider span enables the
downspeeding when driving outside the city limits

increase the climbing ability
when driving over mountain passes or off-road

or when towing a trailer

[13] ${\tfrac {i_{n}}{i_{1}}}$

[14] A wider span enables the
downspeeding when driving outside the city limits

increase the climbing ability
when driving over mountain passes or off-road

or when towing a trailer

[15] wnspeeding when driving outside the city limits

[16] rease the climbing ability
when driving over mountain passes or off-road

or when towing a trailer

[17] when driving over mountain passes or off-road

[18] r when towing a trailer

[15] Ratio Span's Center
$(i_{n}i_{1})^{\tfrac {1}{2}}$

The center indicates the speed level of the transmission

Together with the final drive ratio

it gives the shaft speed level of the vehicle

[20] $(i_{n}i_{1})^{\tfrac {1}{2}}$

[21] The center indicates the speed level of the transmission

[22] Together with the final drive ratio

[23] t gives the shaft speed level of the vehicle

[16] Average Gear Step
$({\tfrac {i_{n}}{i_{1}}})^{\tfrac {1}{n-1}}$

With decreasing step width
the gears connect better to each other

shifting comfort increases

[25] $({\tfrac {i_{n}}{i_{1}}})^{\tfrac {1}{n-1}}$

[26] With decreasing step width
the gears connect better to each other

shifting comfort increases

[27] the gears connect better to each other

[28] shifting comfort increases

[17] Sun 1: sun gear of gearset 1

[18] Ring 1: ring gear of gearset 1

[19] Sun 2: sun gear of gearset 2

[20] Ring 2: ring gear of gearset 2

[21] Sun 3: sun gear of gearset 3

[22] Ring 3: ring gear of gearset 3

[23] Sun 4: sun gear of gearset 4

[24] Ring 4: ring gear of gearset 4

[50:50-25] ^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k Standard 50:50
— 50 % Is Above And 50 % Is Below The Average Gear Step —
With steadily decreasing gear steps (yellow highlighted line Step)

and a particularly large step from 1st to 2nd gear
the lower half of the gear steps (between the small gears; rounded down, here the first 3) is always larger

and the upper half of the gear steps (between the large gears; rounded up, here the last 4) is always smaller

than the average gear step (cell highlighted yellow two rows above on the far right)

lower half: smaller gear steps are a waste of possible ratios (red bold)

upper half: larger gear steps are unsatisfactory (red bold)

[38] With steadily decreasing gear steps (yellow highlighted line Step)

[39] rticularly large step from 1st to 2nd gear
the lower half of the gear steps (between the small gears; rounded down, here the first 3) is always larger

and the upper half of the gear steps (between the large gears; rounded up, here the last 4) is always smaller

[40] the lower half of the gear steps (between the small gears; rounded down, here the first 3) is always larger

[41] the upper half of the gear steps (between the large gears; rounded up, here the last 4) is always smaller

[42] than the average gear step (cell highlighted yellow two rows above on the far right)

[43] wer half: smaller gear steps are a waste of possible ratios (red bold)

[44] upper half: larger gear steps are unsatisfactory (red bold)

[R:1-26] ^ ^a ^b ^c ^d ^e ^f ^g Standard R:1
— Reverse And 1st Gear Have The Same Ratio —
The ideal reverse gear has the same transmission ratio as 1st gear
no impairment when maneuvering

especially when towing a trailer

a torque converter can only partially compensate for this deficiency

Plus 11.11 % minus 10 % compared to 1st gear is good

Plus 25 % minus 20 % is acceptable (red)

Above this is unsatisfactory (bold)

[46] The ideal reverse gear has the same transmission ratio as 1st gear
no impairment when maneuvering

especially when towing a trailer

a torque converter can only partially compensate for this deficiency

[47] rment when maneuvering

[48] specially when towing a trailer

[49] torque converter can only partially compensate for this deficiency

[50] Plus 11.11 % minus 10 % compared to 1st gear is good

[51] Plus 25 % minus 20 % is acceptable (red)

[52] Above this is unsatisfactory (bold)

[1:2-27] Standard 1:2
— Gear Step 1st To 2nd Gear As Small As Possible —
With continuously decreasing gear steps (yellow marked line Step)

the largest gear step is the one from 1st to 2nd gear, which
for a good speed connection and

a smooth gear shift

must be as small as possible
A gear ratio of up to 1.6667:1 (5:3) is good

Up to 1.7500:1 (7:4) is acceptable (red)

Above is unsatisfactory (bold)

[54] With continuously decreasing gear steps (yellow marked line Step)

[55] the largest gear step is the one from 1st to 2nd gear, which
for a good speed connection and

a smooth gear shift

[56] r a good speed connection and

[57] smooth gear shift

[58] ust be as small as possible
A gear ratio of up to 1.6667:1 (5:3) is good

Up to 1.7500:1 (7:4) is acceptable (red)

Above is unsatisfactory (bold)

[59] A gear ratio of up to 1.6667:1 (5:3) is good

[60] Up to 1.7500:1 (7:4) is acceptable (red)

[61] Above is unsatisfactory (bold)

[LS-28] From large to small gears (from right to left)

[step-29] ^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m ⁿ ^o ^p ^q ^r ^s ^t ^u ^v ^w ^x ^y Standard STEP
— From Large To Small Gears: Steady And Progressive Increase In Gear Steps —
Gear steps should
increase: Δ Step (first green highlighted line Δ Step) is always greater than 1

As progressive as possible: Δ Step is always greater than the previous step

Not progressively increasing is acceptable (red)

Not increasing is unsatisfactory (bold)

[64] Gear steps should
increase: Δ Step (first green highlighted line Δ Step) is always greater than 1

As progressive as possible: Δ Step is always greater than the previous step

[65] increase: Δ Step (first green highlighted line Δ Step) is always greater than 1

[66] As progressive as possible: Δ Step is always greater than the previous step

[67] Not progressively increasing is acceptable (red)

[68] Not increasing is unsatisfactory (bold)

[speed-30] ^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m Standard SPEED
— From Small To Large Gears: Steady Increase In Shaft Speed Difference —
Shaft speed differences should
increase: Δ Shaft Speed (second line marked in green Δ (Shaft) Speed) is always greater than the previous one

1 difference smaller than the previous one is acceptable (red)

2 consecutive ones are a waste of possible ratios (bold)

[70] Shaft speed differences should
increase: Δ Shaft Speed (second line marked in green Δ (Shaft) Speed) is always greater than the previous one

[71] increase: Δ Shaft Speed (second line marked in green Δ (Shaft) Speed) is always greater than the previous one

[72] 1 difference smaller than the previous one is acceptable (red)

[73] 2 consecutive ones are a waste of possible ratios (bold)

[31] Model year 2016

[33] Model year 2015

[swap-35] Adjusted formulas with gearset 1 and 3 swapped

[36] Permanently coupled elements
S₁ and R₂

C₁ (carrier 1) and C₄ (carrier 4)

S₂ and S₃

C₃ (carrier 3) and R₄

[78] S₁ and R₂

[79] C₁ (carrier 1) and C₄ (carrier 4)

[80] S₂ and S₃

[81] C₃ (carrier 3) and R₄

[37] Blocks S₂ and S₃

[38] Blocks R₃

[39] Couples C₂ and S₄ with the turbine

[40] Couples R₁ with S₄

[41] Couples S₁ and R₂ with S₄

[42] without generation designation

[43] First transmission on the market to use the dedicated 8-speed layout
gearset 1 and 3 not swapped

for comparison purposes only

[89] rset 1 and 3 not swapped

[90] r comparison purposes only

[noswap-46] Original formulas
gearset 1 and 3 not swapped

for comparison purposes only

[92] rset 1 and 3 not swapped

[93] r comparison purposes only

[std-47] Standard

[48] 3.6 L engine

[51] Z51

[54] Maximum Trailering Package

[engine-55] 2.8 L diesel engine and 4.3 L gas engine only

[USA_Info_2018-1] "USA Information Guide Model Year 2018" (PDF). Retrieved 15 July 2019.

[2] "Cadillac Introduces New 8-Speed Automatic on CT6". Cadillac Media USA. Cadillac Media USA. 20 March 2015. Retrieved 20 March 2015.

[4] "New 8-Speed Enables Quicker, More Efficient Corvette". www.gm.com. General Motors. 20 August 2014. Archived from the original on 22 December 2014. Retrieved 21 August 2014.

[6] "Timur Apakidze · Saturation Dive: The GM 8L 90 8-Speed Transmission". TTAC: The Truth About Cars. 23 April 2014. Retrieved 12 April 2024.

[7] ttps://poweredsolutions.gm.com/products/8l45-8-speed-transmission/

[8] ttps://poweredsolutions.gm.com/products/8l90-8-speed-transmission/

[32] "Transmission Repair Cost Guide". Retrieved 15 July 2019.

[34] "WIT · Whatever It Takes · Automatic Transmission Parts Catalog 2018+2019 Page 268". Retrieved 15 July 2019.

[70sun1+2-44] 8HP 70 Repair Manual · Picture 10106 p. 110 · Saarbruecken 2014 · https://avtgr.ru/upload/data/pdf/zf_instructions/8HP70.pdf

[dive-45] "Timur Apakidze · Saturation Dive: ZF 8-Speed Automatic". TTAC: The Truth About Cars. 11 March 2014. Retrieved 7 July 2019.

[49] "2015 Cadillac Escalade Updated with 8L90 8-Speed Automatic and More Tech [Photo Gallery]". 11 August 2014. Retrieved 12 August 2014.

[50] "Chevrolet Confirms 2015 Corvette Stingray To Utilize 8L90 Eight-Speed Gearbox". Retrieved 9 April 2014.

[52] "Supercharged 2015 Chevy Corvette Z06 takes the C7 beyond the ZR1 [w/video]". Retrieved 25 January 2014.

[engine-53] "GM confirms 2015 Silverado, Sierra to get 8-speed automatic". Retrieved 18 June 2014.

[56] "Class Action Lawsuit Filed Over Alleged Shifting Defect in Certain General Motors Transmissions". 19 December 2018. Retrieved 2 February 2019.

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