10L1000 ATSG Manual

This ATSG GM & Allison 10L1000 TechTran manual walks through the complete teardown and reassembly process of the 10L1000 transmission, along with detailed diagnostic insights to support accurate service and troubleshooting.

Introduced for the 2020 model year, the 10L1000 is used in Chevrolet and GMC 2500 and 3500 trucks equipped with both the 6.6L Duramax diesel and 6.6L gas engines. While commonly associated with Allison branding, this unit is manufactured by GM, with Allison serving in a design and engineering role. Internally, it shares noticeable similarities with the 10L90 once disassembled.

The 10L1000 is a fully electronic, rear-wheel-drive, 10-speed automatic transmission. Its gear ratios are achieved through a combination of four simple planetary gear sets, two stationary clutches, and four rotating clutches. This layout allows for a compact, on-axis design that incorporates a low-profile torque converter, an off-axis pump, and tightly packaged gear sets. By positioning the rotating clutches forward, fluid passages are shortened, helping improve shift response and efficiency.

The case features an integrated bellhousing to increase structural rigidity across the powertrain. A unique off-axis pump drive system allows the variable vane pump to sit lower in the transmission, improving packaging while maintaining consistent fluid delivery. This pump design effectively operates like two pumps in one, helping prevent priming issues while reducing parasitic loss and optimizing fluid routing throughout the system.

Control is handled by an externally mounted transmission control module (TCM), which allows for greater flexibility in vehicle integration. The system relies on multiple speed sensors to provide precise data, enabling accurate and responsive shift timing.

The torque converter is a four-element design consisting of a pump, turbine, stator, and a pressure plate connected to the turbine. It functions as a fluid coupling for smooth power transfer, while also providing torque multiplication under load. When the clutch is applied, it creates a direct mechanical connection between the engine and transmission.

Gear changes are fully automatic and controlled by the Delphi T87A TCM, which continuously monitors input from various sensors to determine optimal shift timing. Hydraulic pressure is generated by the off-axis variable vane pump and distributed through dual valve body assemblies, applying or releasing clutch packs as needed.

Inside the transmission, six multi-disc clutch assemblies are used to produce ten forward speeds and one reverse. These clutches engage in different combinations to route power through the planetary gear sets and out through the output shaft.

The 10L1000 is available in both two-wheel and four-wheel drive configurations, with optional PTO-equipped variants identified by RPO codes MGM and MKM, as well as non-PTO versions under RPO code MGU. The unit referenced in this manual is an MGM configuration, equipped with PTO functionality.