GM-Allison 10L1000 Automatic Transmission

The General Motors Allison 10L1000 is a ten speed automatic transmission first introduced for the 2020 GMC Sierra HD and Chevrolet Silverado HD. Although it was originally limited to the 6.6 liter Duramax engine, it became standard for GM's 6.6 liter gasoline V-8 beginning in 2024. The transmission is often confused with the GM 10L80 & Ford 10R80 ten speed automatic transmission that GM co-developed with Ford Motor Company, but the 10L1000 is not the direct result of this collaboration.

The GM-Allison Relationship

The Allison Transmission division of General Motors became a household name in the early 2000's when GM began putting Allison 1000 series transmissions in Silverado and Sierra pickup trucks equipped with the 6.6 liter Duramax Diesel engine. Although GM would sell Allison in 2007, they continued to supply transmissions for GMC and Chevrolet trucks equipped with the venerable Duramax Diesel. In fact, the names would become complimentary, as if you couldn't say "Duramax" without "Allison".

Fast forwarding to 2020, GM introduced the "Allison" 10L1000 ten speed automatic transmission. The 10L1000, however, is designed, engineered, and produced entirely by General Motors. Although GM specifically noted that this transmission was "validated" by Allison through rigorous testing and review, the specifics behind this statement are unknown. The 10L1000 is branded as an Allison unit as the result of a simple licensing agreement between the two companies. In fact, this agreement briefly lapsed before it was renewed for the 2026 model year.

Transmission Specs

[1] - Total transmission system capacity; pan removal and filter replacement is expected to require approximately 15 quarts to replenish fluid.

[2] - Power take-off clutch solenoid is commanded OFF when transmission is not in park or gears 1 through 5.

Gear Ratios

Gear Steps (Percent Step)

Features

• 10 Forward Speeds - The 10L1000 features a deep 4.54 to 1 reduction in first gear and tall 0.63 to 1 overdrive in 10th, maximizing pulling power at low speeds while keeping the engine speed low while cruising. Additionally, this transmission has a favorable 25% average step between gear changes that prevents an abrupt dive in engine torque as it runs through its shift sequence. Furthermore, the broad gear ratio range permits the use of taller differential ratios without sacrificing overall performance.
• Tow/Haul Mode - An aggressive shift schedule and torque converter lockup strategy that holds gears longer when hauling heavy loads to refrain the transmission from up-shifting at inopportune moments and to maintain vehicle speed on steep descents.
• Adaptive Control - 10L1000 transmissions perpetually monitor and adjust shift parameters through a process called adaptive control. Data from each shift is collected and compared to predetermined, "expected" values. Adjustments are made based on this data, which maintains shift feel and performance as the transmission wears.
• 2nd Gear Starts - When the "Tow/Haul" mode is not active, the transmission starts in 2nd gear for a smoother take-off and to avoid a harsh 2nd to 1st downshift at slow speeds.
• Fully Integrated PTO - When properly equipped (RPO code MGU) the 10L1000 features a fully integrated power take-off system that is driven directly off the engine. This allows for full use of PTO equipment while the vehicle is stationary or in motion.
• Converter Lockup in All Forward Gears - Torque converter lockup creates a mechanical connection between the engine and transmission (as opposed to being coupled by fluid when unlocked), reducing heat buildup in the fluid during low speed, high load operation.
• Off-Axis Variable Vane Transmission Fluid Pump - Unlike a traditional automatic transmission where the fluid pump is mounted axially behind the torque converter, the 10L1000 uses an off-axis transmission fluid pump that is gear driven off the input shaft. Replacing the pump is therefore possible without removing the transmission from the vehicle; it is accessible through the bottom of the transmission case and only the pan needs to be removed.
• Manual Shift Mode - Placing the range selecting in the "L" position allows the operator to manually control transmission shifting using the "+" and "-" buttons to perform up-shifts and downshifts, respectively. This mode is more appropriately identified as "Range Selection Mode" because the TCM may still command downshifts if required but it will not up-shift beyond the current listed gear, i.e. if "L5" is displayed, the transmission may downshift to 4th gear but will not up-shift beyond 5th gear.

Identification

The 10L1000 ten speed automatic transmission is the only transmission available in 2020 to current Chevrolet Silverado 2500/3500 HD and GMC Sierra 2500/3500 HD pickup and chassis cab trucks equipped with the 6.6 liter Duramax diesel engine. For 2024 to current 2500/3500 HD vehicles equipped with the 6.6 liter gasoline V-8 engine, the 10L1000 has been the only available transmission.

All vehicles that have the 6.6 liter Duramax diesel V-8 engine and the 10L1000 automatic transmission without PTO provisions will have RPO code MGM. All vehicles that have the 6.6 liter Duramax diesel V-8 engine and the 10L1000 automatic transmission with PTO provisions will have RPO code MGU. Finally, all vehicles equipped with the 6.6 liter gasoline V-8 engine and 10L1000 automatic transmission will have RPO code MKM. Power take-off provisions are not available on trucks equipped with the gasoline V-8 engine.

Confusion with 10R80, 10L80, 10R140 Transmissions

The GM 10L1000 and Ford 10R140 heavy duty ten speed automatic transmissions are often confused with the GM 10L80 and Ford 10R80 transmissions. Because of this confusion, it is often stated that the 10L1000 transmission was co-developed with Ford Motor Company; this statement is entirely false.

General Motors and Ford Motor Company co-developed the 10L80/10R80 transmission. The parts commonality between the GM 10L80 and Ford 10R80 is the direct reflection of this collaboration. These transmissions are used in the GMC Sierra/Chevrolet Silverado 1500 and Ford F-150, respectively.

Ford's heavy duty ten speed transmission is the 10R140 TorqShift, which bears no resemblance and shares no components with GM's 10L1000.

Lubrication & Service Requirements

GM requires that this transmission is serviced at 45,000 mile intervals. A typical service involves draining and replenishing the automatic transmission fluid and replacing the sump filter. Between 14 and 15 quarts of fluid is expected to drain when this service is completed, although the actual amount will vary unit-to-unit due to uncontrollable variables. Failure to service the transmission per factory recommendations may result in accelerated component wear and particle accumulation in the fluid.

10L1000 transmissions use GM Dexron Ultra Low Viscosity (ULV) automatic transmission fluid; any ATF used in this transmission must explicitly meet Dexron ULV specifications.

Shift Solenoids

The 10L1000 transmission employs a total of (8) electronic solenoids to perform shift functions. Each of these solenoids are mounted to the valve body of the transmission. If the transmission is equipped with a PTO (RPO code MGU only), a 9th solenoid is necessary but it is positioned in the PTO unit, not the valve body. The solenoids are:

• Shift Solenoid A (SSA) - transmission control solenoid valve 1, "A" position in valve body; controls 1-2-3-4-5-6-R clutch
• Shift Solenoid B (SSB) - transmission control solenoid valve 2, "B" position in valve body; controls 1-2-8-9-10-R clutch
• Shift Solenoid C (SSC) - transmission control solenoid valve 3, "C" position in valve body; controls 2-3-4-5-7-9-10 clutch
• Shift Solenoid D (SSD) - transmission control solenoid valve 4, "D" position in valve body; controls 4-5-6-7-8-9-10-R clutch
• Shift Solenoid E (SSE) - transmission control solenoid valve 5, "E" position in valve body; controls 1-3-5-6-7-8-9 clutch
• Shift Solenoid F (SSF) - transmission control solenoid valve 6, "F" position in valve body; controls1-2-3-4-6-7-8-10-R clutch
• Pressure Solenoid - transmission control solenoid valve 7, "L" position in valve body; controls line pressure
• Torque Converter Lockup Solenoid (TCC) - transmission control solenoid valve 8, "T" position in valve body; controls torque converter lockup
• Power Take-Off Solenoid - transmission control solenoid valve 9, this control valve is mounted in the PTO unit, not the valve body

All (6) shift solenoids (SSA through SSF) are linear type, normally low (OFF) solenoids. The torque converter lockup solenoid is a normally low, variable force solenoid in which the fluid pressure on the output side of the valve increases proportionately to an increase in electrical current delivered across its terminals. The PTO solenoid is a simple ON/OFF type that is normally closed. When current is applied across the terminals of this solenoid, it switches "ON" and fluid pressure applies the PTO clutch.

Transmission control solenoid 7 (position "L" in the valve body, line pressure) is a normally high (ON), variable force solenoid. Maximum line pressure is therefore achieved when there is no electrical current delivered across its terminals, and the pressure decreases proportionately to an increase in electrical current delivered across its terminals. It is the only normally high solenoid and it is designed this way so that if this solenoid loses power it increases the transmission line pressure. This is opposed to abruptly losing line pressure due to an electrical malfunction, which would likely result in severe component damage.

All shift solenoids are factory flow tested. This process creates a mathematical relationship between the electrical current applied to the solenoid and the actual fluid pressure. This information is programmed into the transmission control module, thus anytime a shift solenoid is replaced the values stored in the TCM must be updated - it is not a simple out with the old, in with the new operation as it has been with previous transmissions.

Solenoid Resistance Chart

[3] - Resistance range expected from properly functioning shift solenoid at 68 °F, as measured across the terminals of the solenoid.

Solenoid Apply Chart

[4] - Only "ON" during high speed shift into neutral

Author - T. List
Editor, Diesel Hub