* Size and Strength: The TH400 is significantly larger and more robust than the TH350. It's designed to handle considerably more torque, making it ideal for high-performance applications and larger, heavier vehicles. The TH350 is better suited for lighter vehicles and applications where high torque isn't needed.
* Gear Ratios: While both are three-speed transmissions, they have different gear ratios. The TH400 generally has lower gear ratios, providing more pulling power at lower speeds but a lower top speed for a given engine RPM. The TH350 offers a slightly wider spread of ratios, offering a bit more versatility. Specific ratios varied depending on the application and year.
* Construction: The TH400 has a stronger case, heavier internal components, and a different planetary gearset designed for higher torque capacity. This contributes to its greater durability under heavy load.
* Overdrive: Neither transmission inherently includes an overdrive gear. Overdrive was not common in these transmissions when originally produced. While aftermarket overdrive units can be added, it's more common to see it done with a TH350 due to its lighter weight.
* Applications: The TH350 saw widespread use in many GM passenger cars and lighter trucks. The TH400 was preferred for heavier trucks, performance cars, and applications requiring high torque handling.
In short: The TH400 is a heavy-duty transmission built for power and durability, while the TH350 is a more compact and lighter-duty option. The choice between them depends entirely on the application and the power requirements of the vehicle.
