Rebuilding the TH350 Transmission: A Comprehensive Guide

Lillian Nelson

The TH350 transmission, manufactured by General Motors, has been a workhorse in the automotive industry for decades. Known for its durability and simplicity, the TH350 has found its way into countless classic cars, trucks, and hot rods. However, like any mechanical component, it eventually requires maintenance and rebuilding. In this article, we delve into the intricacies of rebuilding a TH350 transmission, step by step.

1. Understanding the TH350 Transmission

Before diving into the rebuilding process, let's explore the basics of the TH350:

What Is the TH350?

The TH350, also known as the Turbo-Hydramatic 350, is a three-speed automatic transmission. It was first introduced in the 1969 model year and remained in production until the early 1980s. The TH350 was commonly found in GM vehicles, including Chevrolet, Buick, Oldsmobile, and Pontiac.

Key Features:

  • Three Forward Gears: The TH350 offers three forward gears (Drive, Second, and First) and reverse.
  • Hydraulic Operation: It relies on hydraulic pressure to engage clutches and bands.
  • Simplicity: The TH350 lacks electronic controls, making it straightforward to work on.
  • Durability: Its robust design ensures longevity under normal driving conditions.

2. Signs That Your TH350 Needs Rebuilding

Before embarking on a rebuild, recognize the symptoms indicating transmission issues:

Common Signs:

  1. Slipping Gears: If your TH350 slips out of gear or hesitates during shifts, it's time for attention.
  2. Fluid Leaks: Puddles of transmission fluid under your vehicle signal leaks.
  3. Harsh Shifting: Rough gear changes or sudden jerks indicate wear.
  4. Noisy Operation: Unusual noises (whining, grinding) during operation require investigation.

3. Gathering Tools and Parts

To rebuild a TH350, assemble the following:

Essential Tools:

  • Socket Set and Wrenches
  • Torque Wrench
  • Snap Ring Pliers
  • Seal Puller
  • Transmission Jack or Support Stand

Replacement Parts:

  • Master Rebuild Kit: Includes gaskets, seals, clutches, and bands.
  • Filter and Pan Gasket
  • Front and Rear Seals
  • Thrust Washers
  • Modulator Valve

4. Disassembly

Begin by removing the transmission from the vehicle:


  1. Drain Fluid: Remove the pan and drain the transmission fluid.
  2. Detach Linkages: Disconnect the shift linkage and kickdown cable.
  3. Remove Bellhousing Bolts: Separate the transmission from the engine.
  4. Disassemble Valve Body: Remove the valve body, separator plate, and shift solenoids.
  5. Inspect Components: Check clutches, bands, and gears for wear.

5. Reassembly

Now, let's put it all back together:

Reassembly Steps:

  1. Install New Seals: Replace front and rear seals.
  2. Rebuild Clutches and Bands: Follow the kit instructions.
  3. Reassemble Valve Body: Ensure proper alignment.
  4. Torque Converter Installation: Align the converter with the pump.
  5. Adjust Bands and Linkages: Set proper clearances.
  6. Fill with Fluid: Use the correct ATF type.

6. Testing and Adjustments

After reinstallation, perform these checks:


  1. Pressure Test: Verify hydraulic pressure.
  2. Shift Quality: Test gear changes.
  3. Road Test: Drive to assess performance.


Rebuilding a TH350 transmission requires patience, attention to detail, and the right tools. While challenging, it's a rewarding process that ensures your classic ride continues to shift smoothly down the road.

Remember to consult your vehicle's service manual and follow safety precautions throughout the rebuild. Happy wrenching! ️

Also Read