GM 8L transmission

The 8L is the first 8-speed automatic transmission built by General Motors. All 8L transmissions are based on the same globally patented gearset concept as the ZF 8HP from 2008 and, like this, are designed for longitudinal engine installation and features a hydraulic (Hydramatic) design. While fully retaining the same gearset logic, they differ only in the patented arrangement of the components, with planetary gearsets 1 and 3 swapped. and

History

2014: 8L 90 M5U

The 8L 90 was introduced in 2014 and is designed to be either attached to the front-located engine with a standard bell housing or mounted in the rear of the car adjacent to the differential (as in the Corvette).

2015: 8L 45 M5N

The 8L 45 is the smaller variant and was launched in 2015 in the 2016 Cadillac CT6. It is always attached to the front-located engine with a standard bell housing. It shares much with the 8L 90 transmission. Estimated weight savings over the heavier-duty 8L 90 is .

2023: 8L 80 MFC/N8X and 8L 45 N8R

The 8L 80 is an updated version with new RPO codes MFC and N8X and was introduced on the 2023 model years of the Chevrolet Colorado and GMC Canyon. A second generation of the 8L 45 was introduced in 2023 model years with a new RPORegular production option code N8R.

Key data

+ Gear ratios Model Type FirstDelivery Gear Total Span Avg.Step Components Nomenclature R 1 2 3 4 5 6 7 8 Nomi-nal Effec-tive Cen-ter Total perGear GearsCount Cou-pling Gear-sets Maximum Input Torque 8L 90 · 8L 80 M5U · MFC+N8X 2014 · 2023 4 Gearsets2 Brakes3 Clutches 8 L 8L 45 M5N · N8R 2015 · 2023 ZF 8HP 70 2008 H P –

Specifications

+ Features 8L 45 M5N + N8R 8L 90 M5U8L 80 MFC + N8X Input capacity Maximum engine power Maximum gearbox torque Maximum shaft speed 7,500/min 6,000/min Vehicle Maximum validated weightGross vehicle weight · GVW — — Maximum validated weightGross curbvehicle weight · GCVW Sundry 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 Fluid type DEXRON high performance ATF Fluid capacity Weight Available control featuresShift 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/stopAutomatic grade braking Assembly sites GMPT Toledo · Ohio · USAGMPT Silao · Mexico

Planetary gearset concept

Improved fuel economy

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), which is a decisive factor in improving energy efficiency and thus reducing fuel consumption. In addition, the lower engine speed level improves the noise-vibration-harshness comfort and the exterior noise is reduced. Due to changes in internal design, the shift times are reduced to 0.2 seconds.

Reduced manufacturing complexity

In order to avoid a further increase in manufacturing complexity while expanding the number of gear ratios, ZF and consequently GM switched from the conventional design method—in which the planetary gearset concept was limited to a purely serial or in-line power flow—to a more modern design method that utilizes a planetary gearset concept with combined parallel and serial power flow. 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 8HP has become the new reference standard (benchmark) for automatic transmissions.

+ Planetary gearset concept: manufacturing complexity WithAssessment Output:GearRatios InnovationElasticityΔ Output : Δ Input Input: Main Components Total Gearsets Brakes Clutches 8LRef. Object Topic Δ Number Relative Δ Δ Output · Δ Input 8L6L 86 Progress 98 43 22 33 Δ Number 2 1 1 0 0 Relative Δ · 8LZF 8HP 88 CurrentMarket Position 99 44 22 33 Δ Number 0 0 0 0 0 Relative Δ · 8L3-Speed 83 HistoricalMarket Position 97 42 23 32 Δ Number 5 2 2 -1 1 Relative Δ ·

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.

Additionally, 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 brake B and releasing clutch D).

+ Planetary gearset concept: gear ratio quality In-Depth AnalysisWith AssessmentAnd Torque RatioAnd Efficiency Calculation Planetary Gearset: Teeth Count Nomi-nalEffec-tive Cen-ter Avg. ModelType VersionFirst Delivery S1R1 S2R2 S3R3 S4R4 BrakesClutches RatioSpan GearStep Gear R 1 2 3 4 5 6 7 8 GearRatio Step Δ Step ShaftSpeed Δ ShaftSpeed TorqueRatio Efficiency 8L 90-M5U8L 80-MFC8L 80-N8X 2014 · 2023 4179 4686 3773 2589 23 Gear R 1 2 3 4 5 6 7 8 GearRatio 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 TorqueRatio –3.6149–3.5155 4.488874.4532 2.90392.8704 2.05352.0255 1.66501.6385 1.25781.2516 1.0000 0.84110.8409 0.64690.6446 Efficiency 0.94690.9209 0.98440.9766 0.97740.9662 0.98960.9761 0.98660.9709 0.99040.9855 1.0000 0.99480.9945 0.99290.9893 8L 45M5N 2015 · 2023 4179 4179 4179 2694 23 Gear R 1 2 3 4 5 6 7 8 GearRatio 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 TorqueRatio –3.7202–3.6185 4.54314.5069 2.97012.9360 2.04352.0328 1.63661.6258 1.24681.2408 1.0000 0.84510.8428 0.65380.6514 Efficiency 0.94720.9213 0.98430.9765 0.97750.9663 0.98970.9845 0.98690.9804 0.99050.9858 1.0000 0.99490.9923 0.99310.9895 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 Geometric ratios: speed conversion GearRatioR & 1 & 2OrdinaryElementaryNoted GearRatio3 & 4OrdinaryElementaryNoted GearRatio5OrdinaryElementaryNoted GearRatio6 – 8OrdinaryElementaryNoted Kinetic ratios: torque conversion TorqueRatioR & 1 & 2 TorqueRatio3 & 4 TorqueRatio5 TorqueRatio6 – 8 8HP70 2008 488HP 70 Repair Manual · Picture 10106 p. 110 · Saarbruecken 2014 · https://avtgr.ru/upload/data/pdf/zf_instructions/8HP70.pdf96 4896 69111 2385 23 Gear R 1 2 3 4 5 6 7 8 GearRatio 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 TorqueRatio –3.1186–3.0313 4.62174.5848 3.06033.0253 2.08202.0709 1.64461.6336 1.27201.2658 1.0000 0.83470.8324 0.66220.6599 Efficiency 0.94600.9195 0.98430.9764 0.97760.9664 0.98960.9843 0.98670.9802 0.99030.9854 1.0000 0.99470.9920 0.99320.9898 GearRatioR & 1 & 2 GearRatio3 & 4 GearRatio5 GearRatio6 – 8

Lawsuits and issues

8L 45 and 8L 90 transmissions manufactured between 2015 and 2019 suffer from two different, unrelated problems. The first is that the 8L’s transmission fluid can absorb moisture from the air via the vent system, especially in humid climates, which can cause the clutches to slip. This can cause some customers, especially those driving in high gears, to feel a “shake/shudder feeling” akin to driving over rumble strips or rough pavement. Introduction of moisture-resistant transmission fluid in December 2018 largely resolved this issue. The second issue is that when changing gears 8L transmissions sometimes apply too much pressure and fail to purge trapped air leaking into the valves. This issue can cause jerkiness or hard shifting when upshifting or downshifting, and other issues. This issue was resolved with the redesigned gen II transmissions, but cannot be repaired on affected transmissions.

These issues are 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. As of 2025, the class action had been remanded to the district court for procedural issues.https://www.opn.ca6.uscourts.gov/opinions.pdf/25a0170p-06.pdf This article incorporates public domain text from this source.

Applications

+ Variants and applications Make Model Years Model Final Drive Ratio 8L 90 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 8L 80 Chevrolet 2023–present Colorado 2024–present Silverado GMC 2023–present Canyon 8L 45 Cadillac 2016–2019 ATS 2016–2019 CTS 2020–present CT4 2016–present CT6 Chevrolet 2016–2023 Camaro LT (2.0L) 3.27 2016–2019 Camaro LT (3.6L) 2.77 2017–present Colorado 3.42 GMC 2017–present Canyon

GM 8L transmission

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