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The Turbo 400 is about the easiest automatic in the world to rebuild well. Three speeds, one band, four clutch packs, a sprag, a roller clutch, and a valve body with no electronics at all. Units built in 1965 go back together with the same kit as units built in the 1990s. That is also why there are so many kits on the market with confusing names. Here is what the names mean and which one to buy.
Kit Levels, Decoded
| Kit | Typically Includes | Who It Is For |
|---|---|---|
| Overhaul kit | Gaskets, lip seals, metal-clad seals (front and rear), sealing rings, O-rings | You already have good frictions, or you are buying clutches separately to choose your own. |
| Master kit | Overhaul kit plus a full set of frictions and steels, usually a filter | The normal rebuild. Most builders start here. |
| Master kit with pistons | Master kit with molded (bonded) pistons instead of loose lip seals | Anyone who wants fewer rolled seals on assembly. Worth the money. |
| Banner / Level 2+ | Master kit plus band, bushings, modulator, sometimes a filter and high-energy frictions | High-mileage units where you already know the band and bushings are shot. |
Read the actual contents list, not the name. One seller's "master" is another's "overhaul plus." The three things most often left out are the band, the bushing kit, and the vacuum modulator. You will want all three on almost any TH400 that has been in service.
Inspect These Hard Parts First
A new kit in a worn case just makes a new-looking transmission that slips. Before you order, tear down and check:
- Center support. The direct and intermediate clutches are fed through it. Worn sealing ring grooves or a loose bushing and the direct clutch starves — which is the number one TH400 failure: slipping or no 3rd gear. Check ring lands with a new ring for side play.
- Direct drum and forward drum. Look for heat bluing, cracked lugs, and ring-land wear. A cracked direct drum will eat a new clutch pack in a weekend.
- Pump. Check the pump bushing and gear clearances, and the stator shaft bushings. A worn pump bushing is what takes out front seals repeatedly.
- Intermediate sprag and low roller clutch. A worn sprag gives you no 2nd or a neutral-feeling 1-2 shift. See our TH400 no 2nd gear guide.
- Case bushing and governor bore. Rear bushing wear leaks lube; governor bore wear gives you lazy, late upshifts that no shift kit will fix.
- Output shaft and planetaries. Check pinion end play and tooth wear. Street units are usually fine; tow and race units are not always.
What to Add Beyond the Kit
- Band. The TH400's single front band handles manual 2nd and engine braking. A new one is cheap insurance if the old one shows glazing or uneven lining.
- Bushing kit and a driver set. Pump, stator, center support, and case bushings. Use a proper bushing driver so you do not collapse them.
- Vacuum modulator. A leaking diaphragm pulls ATF into the intake: white smoke, fluid loss, and harsh shifts. Match the modulator to your application (stock, high-vacuum, adjustable) instead of grabbing whatever fits.
- Shift kit. A TransGo-style recalibration firms up the 1-2 and 2-3 shifts and adds holding capacity. For a tow rig or anything with real horsepower, install it while the valve body is out.
- Extra direct clutch capacity. Performance builds often run a thinner-steel or extra-plate direct pack. Only do this if you know how to check clearances — too tight and it drags, too loose and it slips.
Assembly Notes That Save Comebacks
- Soak new frictions in the ATF you will run for at least 30 minutes before assembly.
- Check every clutch pack clearance. The kit gives you parts, not clearances. Aftermarket frictions and steels are not always the same thickness as what came out.
- Air check each circuit through the case and center support before the pan goes on. You should hear a clean clunk on apply and no hiss.
- Set front and rear end play with the selective washers. A TH400 with too much end play will chew the thrust bearings.
- Mind the pan and filter. Deep pans need the matching filter and pickup length. The wrong combination sucks air on hard stops and cornering.
Our Pick
For most street, truck, and mild performance builds, a master kit with molded pistons is the right starting point, plus a band, bushings, and a modulator. The TH400 / 3L80 master overhaul kit (22107) covers 1965-up units with frictions, steels, molded pistons, gaskets and the full seal and O-ring set. Browse everything else we carry for the Turbo 400 in the TH400 parts section.
TH400 Kits In Stock
Master overhaul kits with frictions, steels, molded pistons, gaskets and seals for 1965-up Turbo 400 and 3L80 units, plus the hard parts you find worn on teardown.
Shop TH400 Parts → Core Transmission Parts →FAQ
Does one TH400 rebuild kit fit every year?
Nearly. Kits sold for 1965-up cover most Turbo 400 and 3L80 units because the internals changed very little. Check early versus late details like the number of plates in your packs and your pan style before assembly.
What is the difference between a TH400 overhaul kit and a master kit?
An overhaul kit is seals and gaskets only. A master kit adds a full set of frictions and steels, and often a filter. Neither usually includes the band, bushings, or modulator.
Why does my TH400 slip in 3rd after a rebuild?
Most often the direct clutch is not getting full pressure: worn center support ring grooves, a cracked direct drum, or wrong clutch clearance. The kit cannot fix worn hard parts.
Should I install a shift kit during a TH400 rebuild?
For towing or added horsepower, yes. It shortens shift overlap and adds holding capacity, and it is easiest to install while the valve body is already off.