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GM Turbo 400 Automatic Transmission Rebuild Information

History & Information

The General Motors Turbo Hydramatic 400 is a 3 speed automatic transmission with a torque convertor. In 1987 the Turbo 400 was renamed the 3L80 and an HD version for light passenger trucks was named the 3L80HD.The TH 400 is the predecessor to the 3L80, 3L80HD, 4L80E and 4L85E. As of today, the only production vehicles that still use a Turbo Hydramatic 400 are HUMVEE's used in the US Military.

Find out more about your Turbo 400 transmission and how to identify it below.

Identification

GM Turbo 400 Transmission

Oil Pan
Gasket Pattern

Torque Converter
Stall Rating

3 Speed Automatic

13 Bolt-Hole Pattern

1500-1800
RPM's


Rebuilding
Before you get started rebuilding your transmission, you'll need a few parts and tools. You'll need the appropriate transmission rebuild kit for your TH400. Depending on what type of kit you buy, it should come with at least new steels and frictions. Usually included are all the bands, clutches, seals, sealing rings, gaskets and a filter and drain plug. Most higher end rebuild kits will include a new shift kit as well. An automatic transmission shift kit is only needed if you want the gears to shift sooner, but it can also reduce transmission wear by reducing or eliminating shift overlap. The better kits will also include new valves and valve springs for the valve body.

A transmission repair manual is a must. We recommend one for your specific model from ATSG (Automatic Transmission Service Group). Every automatic transmission will need a universal clutch spring compressor as well as snap ring pliers and pic sets for removing valve guides.

Of course you will need to remove the transmission from the motor and chassis. If you're not familiar with this, the first part of the 'Basic Engine Building' video covers this and more. All of the automatic transmission rebuilding video's out there start off with the transmission already out. So be aware if you aren't familiar with removing the transmission. You will also need a good work space and transmission stand. It's best to have it able to rotate around for removing and installing components.

As you disassemble your transmission, make note of any obvious wear to parts that may need replacing. Keep the internal parts in the order they were removed to keep track of everything.

 
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