The TH400. While far from the first automatic transmission ever built, in a sense you could say this was the transmission that started it all. Released in the 60’s during the Golden Era of muscle cars, the TH400 quickly made a name for itself as a strong, reliable transmission that easily held up to the power and torque produced by the BBCs of its day. Even today, 50 years after its debut, the TH400 remains a crowd favorite with a huge following, especially in the drag racing scene. Many street guys prefer the 4L80E over the TH400 due to the addition of Overdrive, lockup and electronic tuning, but some are perfectly content with the TH400 on the street. Depending on your car’s year and model, you may prefer to have a TH400 to keep it more “original”. For drag only cars, a TH400 is often the better choice vs the 4L80E.

North Texas Converter builds an incredibly strong TH400 that we are proud to call our own and many of our customers are proud to call their own now as well. There is an immense amount of customizability available with the TH400 and it has a much larger aftermarket than the 4L80E. The options listed on this page are not the be-all, end-all options for every person. Many will be more than fine with the options on this list, but some may need a higher degree of flexibility when it comes to certain options. Give us a call to discuss your project and we’ll set you up just right!

Base build options

All TH400’s built by us regardless of build level, come with the following options, making even our “entry” level TH400 extremely stout and rated for up to 750hp (Nitrous combos excluded)

  • Full rebuild kit
  • Hi Energy clutches
  • New intermediate/reverse bands
  • New seals
  • New gaskets
  • New filters
  • New bushings throughout
  • New thrust washers
  • New low roller clutch
  • New OEM Borg Warner 34 element sprag
  • New HD intermediate snap ring
  • New Sonnax boost valve w/ spring
  • Rollerized internals
  • 6 count frictions for direct clutches
  • Machine the output shaft for increased yoke spline engagement
  • Dual fed 3rd gear clutches
  • Aluminum deep pan
  • NTC hydraulic modifications throughout

Level I TH400 – Starting at $1,800

The base model TH400 is a very strong, efficient unit, and for most naturally aspirated guys, the buck stops here (although not always!) Warrantied up to 750hp

Level II TH400 – Starting at $2,450

The level II TH400 is just like our level I with the addition of a billet input shaft and forward hub. A must for nitrous users and often the preferred package for the very high horsepower street guys.

The level III TH400 has all the allure of the level II, but with the additional insurance and reliability of a billet main shaft.

An incredibly strong package, this is the strongest the majority of guys will need to go. The addition of the 36 element Pro Mod drum eliminates potential sprag failure and allows you to push the limits of your car or truck to the edge. The aluminum Pro Mod drum is standard at this level, not an upgrade feature.

There are upgrades available beyond this point, but those are typically only needed for strictly drag racers or professionals taking it to a new level. There are a multitude of options, from aftermarket cases, valve bodies, hard parts, you name it. Far too many to list on one page which is why we strongly encourage anyone seriously interested to give us a call and we can discuss your potential options.