What is the difference between 6T30 and 6T40?
At a glance, the 6T40 is the higher-capacity, higher-torque member of GM’s Hydra-Matic 6T family, built to handle mid‑size SUVs and V6 engines, while the 6T30 is a lighter‑duty variant intended for smaller, lower‑torque applications. Both are six‑speed automatic transmissions designed for front‑ and all‑wheel‑drive layouts and share core architecture, but they differ in torque rating, size, gear spread, and typical vehicle applications. Understanding these differences helps explain why automakers pair each unit with different models and engine options.
What they are and where they fit in the Hydra-Matic lineup
The Hydra-Matic 6T family was developed to provide six forward gears in front- or all-wheel-drive platforms. The 6T30 and 6T40 share core architecture but are tuned for different torque loads and vehicle classes.
- Torque capacity and power handling: 6T40 generally handles higher peak torque than 6T30, making it suitable for mid-size SUVs and engines with higher outputs; 6T30 is designed for lighter-duty applications with lower torque.
- Physical size and weight: The 6T40 is physically larger and heavier due to its reinforced components and longer gear-set; the 6T30 is more compact and lighter.
- Gear ratio spread and performance: The 6T40 often features a broader overall gear-span to balance acceleration with highway efficiency; the 6T30 uses a narrower spread aligned with lower torque and fuel-economy emphasis.
- Control and maintenance considerations: Both typically use Dexron VI transmission fluid and share similar service intervals, but parts, valve bodies, and clutch packs differ; always verify compatibility with VIN and service data for your model/year.
The differences drive which vehicles they were paired with by manufacturers and influence maintenance decisions for owners and technicians.
Typical vehicle applications and compatibility
These are representative categories; exact model-year availability varies by region and production run. Always check the vehicle's service data to confirm which transmission it uses.
- 6T40: Common in mid-size SUVs and crossovers and in vehicles with higher-torque engines; typically paired with V6 or higher-torque four-cylinder powertrains in GM-group models (and related brands).
- 6T30: Common in compact cars and smaller crossovers with lighter powertrains; used where lower torque capacity and higher efficiency are priorities.
In practice, the choice between 6T30 and 6T40 reflects a balance between space, weight, cost, and expected engine torque loads. Mechanics and owners should match the transmission to the engine and vehicle use case to optimize reliability and performance.
Summary
The 6T40 and 6T30 are related six‑speed automatics within GM’s Hydra‑Matic family. The 6T40 is the stronger, larger, and higher‑torque option designed for bigger vehicles and engines, while the 6T30 is lighter, more compact, and aimed at smaller cars and lower‑torque applications. Both share the six‑speed concept and many design cues, but their gear ratios, physical builds, and torque ratings make them non‑interchangeable in most applications. For buyers and technicians, identifying the correct model for the vehicle is essential to avoid compatibility issues and ensure proper maintenance.
What is the code for the 6T40 transmission?
The Hydra-Matic 6T40 (production code MH8/MHB) is a six-speed automatic transmission produced by General Motors for use in front-wheel-drive vehicles with a transverse powertrain orientation.
What cars have a 6T40 transmission?
The 6T40, referred to in GM inner circles as the GF6, made its debut in the 2008 Chevrolet Malibu, available with the 2.4 L LE5 Ecotec engine making 164 horsepower (122 kW), and has since also been made available on the Chevrolet Cruze, Daewoo Tosca and Buick LaCrosse.
Is the 6T40 a good transmission?
Conclusion. The 6T40 transmission is a versatile and efficient automatic transmission that serves as a reliable option for compact and midsize GM vehicles. Understanding its specifications, recognizing common issues, and maintaining it properly can ensure long-lasting performance.
Is the 6T30 transmission reliable?
While the 6T30 is generally reliable, some common issues have been reported: Shift Flare and Slippage: Often caused by worn clutch packs or valve body issues. Regular maintenance and using high-quality transmission fluid can help prevent this.
