| 8L 45 · 8L 90 | |
| Production: | 2014– |
| Manufacturer: | General Motors |
| Class: | 8-speed longitudinal automatic transmission |
| Related: | ZF 8HP · Aisin-Toyota 8-speed · MB 9G-Tronic |
| 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[1] arrangement of the components with gearsets 1 and 3 swapped.[2]
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[3] with a standard bell housing. It is a hydraulic (hydramatic) design sharing much with the 8L 90 transmission.[4] Estimated weight savings over the heavier duty 8L 90 is 33lb.
The ZF 8HP became the new benchmark for automatic transmissions.
| 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 | ||
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).[8]
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.
| Output: Gear Ratios | Innovation Elasticity Δ Output : Δ Input | Input: Main Components | |||||
|---|---|---|---|---|---|---|---|
| Total | Gearsets | Brakes | Clutches | ||||
| 8L Ref. Object | nO1 nO2 | Topic | nI=nG+ nB+nC | nG1 nG2 | nB1 nB2 | nC1 nC2 | |
| Δ Number | nO1-nO2 | nI1-nI2 | nG1-nG2 | nB1-nB2 | nC1-nC2 | ||
| Relative Δ | Δ Output \tfrac{nO1-nO2 | \tfrac{nO1-nO2 =\tfrac{nO1-nO2 \tfrac{nI2 | Δ Input \tfrac{nI1-nI2 | \tfrac{nG1-nG2 | \tfrac{nB1-nB2 | \tfrac{nC1-nC2 | |
| 8L 6L | 8 6 | Progress | 9 8 | 4 3 | 2 2 | 3 3 | |
| Δ Number | 2 | 1 | 1 | 0 | 0 | ||
| Relative Δ | \tfrac{1}{3} | \tfrac{1}{3}:\tfrac{1}{8}=\tfrac{1}{3} \tfrac{8}{1}=\tfrac{8}{3} | \tfrac{1}{8} | \tfrac{1}{3} | \tfrac{0}{2} | \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 | \tfrac{5}{3} | \tfrac{5}{3}:\tfrac{2}{7}=\tfrac{5}{3} \tfrac{7}{2}=\tfrac{35}{6} | \tfrac{2}{7} | \tfrac{1}{1} | \tfrac{-1}{3} | \tfrac{1}{2} | |
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.
| 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 {iR} | 1 {i1} | 2 {i2} | 3 {i3} | 4 {i4} | 5 {i5} | 6 {i6} | 7 {i7} | 8 {i8} | |
| Step | -\tfrac{iR}{i1} | \tfrac{i1}{i1} | \tfrac{i1}{i2} | \tfrac{i2}{i3} | \tfrac{i3}{i4} | \tfrac{i4}{i5} | \tfrac{i5}{i6} | \tfrac{i6}{i7} | \tfrac{i7}{i8} | |
| Δ Step | \tfrac{i1}{i2}:\tfrac{i2}{i3} | \tfrac{i2}{i3}:\tfrac{i3}{i4} | \tfrac{i3}{i4}:\tfrac{i4}{i5} | \tfrac{i4}{i5}:\tfrac{i5}{i6} | \tfrac{i5}{i6}:\tfrac{i6}{i7} | \tfrac{i6}{i7}:\tfrac{i7}{i8} | ||||
| Shaft Speed | \tfrac{i1}{iR} | \tfrac{i1}{i1} | \tfrac{i1}{i2} | \tfrac{i1}{i3} | \tfrac{i1}{i4} | \tfrac{i1}{i5} | \tfrac{i1}{i6} | \tfrac{i1}{i7} | \tfrac{i1}{i8} | |
| Δ Shaft Speed | 0-\tfrac{i1}{iR} | \tfrac{i1}{i1}-0 | \tfrac{i1}{i2}-\tfrac{i1}{i1} | \tfrac{i1}{i3}-\tfrac{i1}{i2} | \tfrac{i1}{i4}-\tfrac{i1}{i3} | \tfrac{i1}{i5}-\tfrac{i1}{i4} | \tfrac{i1}{i6}-\tfrac{i1}{i5} | \tfrac{i1}{i7}-\tfrac{i1}{i6} | \tfrac{i1}{i8}-\tfrac{i1}{i7} | |
| 8L 90 M5U | 900Nm[9] 2014 | 41[10] 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 | ||||||
| Δ Step | 1.1643 | 1.0738 | ||||||||
| Speed | 1.0000 | 1.5349 | 2.1975 | 3.5905 | 4.56 | 6.9991 | ||||
| Δ Speed | 1.0000 | 0.5349 | 0.6626 | 0.8884 | 0.9695 | 1.6057 | ||||
| 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 | ||||||
| Δ Step | 1.1819 | 1.0691 | ||||||||
| Speed | 1.0000 | 1.5190 | 2.2353 | 3.6669 | 4.6154 | 7.0107 | ||||
| Δ Speed | 1.0000 | 0.5190 | 0.7163 | 0.8837 | 0.9485 | 1.5769 | ||||
| Ratio R & even | iR=\tfrac{R2(S1S4-R1R4)}{S1S4(S2+R2)} | i2=\tfrac{R2(S4+R4)}{(S2+R2)S4} | i4=1+\tfrac{S2R3}{S3(S2+R2)} | i6=\tfrac{1}{1} | i8=\tfrac{R2}{S2+R2} | |||||
| Ratio odd | i1=\tfrac{S4+R4}{S4} | \tfrac{(S3+R3)(S4+R4)}{S4R3+S3(S4+R4)} | \tfrac{S3R2R4(S1+R1)+S2S1(S3+R3)(S4+R4)}{S3R4(S1(S2+R2)+R1R2)+S1S2S4(S3+R3)} | \tfrac{R2(S1+R1)}{R2(S1+R1)+S1S2} | ||||||
| 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[11] 96 | 48 96 | 69 111 | 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 | ||||||
| Δ Step | 1.1787 | 1.0779 | ||||||||
| Speed | 1.0000 | 1.5000 | 2.2319 | 3.6555 | 4.6957 | 7.0435 | ||||
| Δ Speed | 1.0000 | 0.5000 | 0.7319 | 0.8382 | 1.0401 | 1.4478 | ||||
| RatioR & Even | iR=\tfrac{R2(S3S4-R3R4)}{S3S4(S2+R2)} | i2=\tfrac{R2(S4+R4)}{(S2+R2)S4} | i4=1+\tfrac{S2R1}{S1(S2+R2)} | i6=\tfrac{1}{1} | i8=\tfrac{R2}{S2+R2} | |||||
| Ratio Odd | i1=\tfrac{S4+R4}{S4} | \tfrac{(S1+R1)(S4+R4)}{S4R1+S1(S4+R4)} | \tfrac{S1R2R4(S3+R3)+S2S3(S1+R1)(S4+R4)}{S1R4(S3(S2+R2)+R2R3)+S2S3S4(S1+R1)} | \tfrac{R2(S3+R3)}{R2(S3+R3)+S2S3} | ||||||
| Cadillac | 2015–2017 | Escalade[12] | 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[13] | 2.41 or 2.73 |
| 2015–2019 | Corvette (C7) Z06[14] | 2.41 | |
| 2019 | Corvette (C7) ZR1 | 2.73 | |
| 2015–present | Silverado[15] | 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 |
| 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 |
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.[16]