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GM 8L transmission

Motor vehicle automatic transmission models From Wikipedia, the free encyclopedia

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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 only in the patented[1] arrangement of the components, with gearsets 1 and 3 swapped.[2]

Quick Facts 8L45 · 8L90 · 8L80, Overview ...

The 8L90 is the first 8-speed automatic transmission built by General Motors. It debut in 2014 and is designed for use in longitudinal engine applications, either attached to the front-located engine[3] with a standard bell housing or mounted in the rear of the car adjacent to the differential (as in the Corvette). It features a hydraulic (Hydramatic) design.

The 8L45 is the smaller variant and debuted 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 8L90 transmission.[4] Estimated weight savings over the heavier-duty 8L90 is 33 lb (15 kg). A second generation of the 8L45 was introduced in 2023 model years and has a new RPO code of "N8R"[5]

The 8L80 is an update to the previous 8L90 version and has a new RPO code of "MFC". Debuted in the 2023 model years of the Chevy Colorado and GMC Canyon.[6]

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Specifications

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More information 8L45-M5N, 8L90-M5U 8L80-MFC N8X ...

Progress Gearset Concept

Main Objectives

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).[10]

Extent

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.

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Quality Gearset Concept

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.

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Applications

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Lawsuits and issues

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8L45 and 8L90 transmissions manufactured between 2015 and 2019 suffer from two different, unrelated problems.[18] 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.[18] Introduction of moisture-resistant transmission fluid in December 2018 largely resolved this issue.[18] 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.[18] 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.[19] As of 2025, the class action had been remanded to the district court for procedural issues.[18]

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References

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