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General Motors · 2014–present

GM 8L45 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.

Text from Wikipedia (CC BY-SA 4.0).

Predecessor: GM 6L50 transmission

All General Motors GM 8L45 transmission data: UK builds, safety, recalls, model years →

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 33 lb (15 kg). 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 RPO code N8R.

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. 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 n

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.

Sections adapted from Wikipedia (CC BY-SA 4.0); text is shortened. Read the full article for the complete history and citations.

Specifications

name
8L 45 · 8L 90 · 8L 80
Production
2014–present
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

Specification summary from Wikipedia (CC BY-SA 4.0). Check the linked sources for citations.

Sources

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