TH375 Transmission: A Comprehensive Guide

The TH375 transmission is a three-speed automatic transmission produced by General Motors (GM) from 1968 to 1990. It was a heavy-duty transmission designed for use in commercial and heavy-duty vehicles, including trucks, buses, and large SUVs. In this article, we will provide a comprehensive guide to the TH375 transmission, including its history, specifications, common issues, and maintenance tips.

History of the TH375 Transmission

The TH375 transmission was first introduced by GM in 1968 as a replacement for the earlier TH400 transmission. It was designed to be a heavy-duty transmission capable of handling high torque and heavy loads, making it ideal for commercial and heavy-duty applications. The TH375 was used in a wide range of GM vehicles, including the Chevrolet C/K series, GMC Sierra, and Cadillac Escalade.

The TH375 remained in production until 1990 when it was replaced by the 4L80E transmission. Despite being replaced, the TH375 remains a popular choice for enthusiasts and restorers due to its durability and reliability.

Specifications of the TH375 Transmission

The TH375 transmission is a three-speed automatic transmission with a maximum torque capacity of 375 lb-ft. It has a 2.48:1 first gear ratio, a 1.48:1 second gear ratio, and a 1.00:1 third gear ratio. The TH375 also features a reverse gear with a 2.08:1 ratio.

The TH375 transmission is a heavy-duty transmission, weighing in at approximately 160 lbs. It uses a cast iron case and tail housing, with an aluminum main body. The TH375 also features a hydraulically controlled lock-up torque converter, which helps to improve fuel efficiency.

Common Issues with the TH375 Transmission

Like any transmission, the TH375 is prone to certain issues over time. Some of the most common issues include:

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Fluid Leaks

One of the most common issues with the TH375 transmission is fluid leaks. Leaks can occur from a variety of locations, including the pan gasket, input shaft seal, and output shaft seal. Fluid leaks can lead to low fluid levels, which can cause the transmission to slip, overheat, or fail.

Torque Converter Lock-Up Issues

The TH375 transmission features a lock-up torque converter, which can sometimes fail to engage or disengage properly. This can cause the engine to stall or lurch, and can also cause transmission overheating.

Shifting Issues

The TH375 transmission may also experience shifting issues, such as delayed or erratic shifts. This can be caused by a variety of issues, including low fluid levels, worn or damaged internal components, or electrical issues.

Maintenance Tips for the TH375 Transmission

To keep your TH375 transmission running smoothly, it’s important to follow these maintenance tips:

Regular Fluid Changes

Regular fluid changes are essential for keeping the TH375 transmission in good condition. The transmission fluid should be changed every 30,000 to 60,000 miles, depending on driving conditions.

Check for Leaks

Regularly check for leaks and address any issues promptly. Leaks can lead to low fluid levels, which can cause the transmission to slip, overheat, or fail.

Avoid Overloading

The TH375 transmission is a heavy-duty transmission, but it still has its limits. Avoid overloading your vehicle or towing more than the recommended weight.

How do I know if I have TH350 or TH400?

Determining whether you have a TH350 or TH400 transmission can be done by identifying specific external features and by examining the vehicle’s specifications. Here are the key differences between the two transmissions:

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The TH400 is a three-speed automatic transmission that was produced by General Motors from 1964 to 1990. Here are some identifying features of the TH400:

Pan Shape and Size

The TH400 transmission pan is rectangular-shaped and measures approximately 16.5 inches long and 13 inches wide. The pan has 13 bolt holes.

Overall Length

The TH400 transmission measures approximately 24.5 inches long from the bell housing to the tailshaft housing.

FAQs

  1. What vehicles were the TH375 transmission used in?
    The TH375 transmission was used in a wide range of GM vehicles, including the Chevrolet C/K series, GMC Sierra, and Cadillac Escalade.
  2. Is the TH375 transmission still in production?
    No, the TH375 transmission was replaced by the 4L80E transmission in 1990.
  3. What is the maximum torque capacity of the TH375 transmission?
    The TH375 transmission has a maximum torque capacity of 375 lb-ft.
  4. How often should the fluid be changed in a TH375 transmission?
    The transmission fluid should be changed every 30,000 to 60,000 miles, depending on driving conditions.

References