Every oil seal, sealing ring and gasket needed to reseal a 1966-1991 GM TH400 during a rebuild, packaged by TCI for street and race builds.
A TH400 that leaks from the bellhousing and tailshaft, engages late after sitting overnight, or slips in one gear while the clutches still look fine usually needs fresh rubber, not new hard parts. TCI part number 228600 is the reseal kit for that job on the 1966-1991 GM Turbo 400 (TH400 / 3L80). TCI packages it for its racing builds and lists it as every soft part an overhaul needs: oil seals, sealing rings, gaskets, the front and rear seals, and a set of valve body gaskets.
Every apply in the TH400 is a hydraulic circuit. Line pressure leaves the pump, travels through the stator shaft and center support, and has to stay sealed past rotating drums by metal and Teflon rings before it can push a clutch piston. Lip seals on the forward, direct and intermediate pistons hold that pressure on the piston face, and the valve body gaskets and separator plate keep circuits from bleeding into each other. When rings wear their grooves, seals harden from heat, or gaskets compress, apply pressure leaks away. The clutch then engages slowly or slips and glazes, which is how the TH400's common worn forward and direct clutch failures usually begin. Replacing the soft parts restores the seal at every one of those points at once.
Put a pressure gauge on the case tap and compare it to the TH400 line pressure chart in idle, Drive and Reverse. Pressure that is low in one range only points to a leak in that circuit; low everywhere points toward the pump. Our TH400 pump failure guide includes GM's pressure figures, and the TH400 delayed engagement guide walks through the engagement checks. If the pan holds metal or lots of lining, you need more than this kit.
TCI lists the 228600 for the 1966-1991 GM TH400, behind GM trucks, motorhomes, big-block cars and swaps. It is a soft-parts kit only: it does not include friction clutches, steel plates, bands, a filter or a pump. The very early 1964-1965 cases and some variant units differ, so if yours is one of those or you are unsure what you have, send us the year, vehicle and VIN, or check the TH350 vs TH400 identification guide. Everything else for the unit is on our TH400 parts page.
If the teardown shows burnt plates, add friction and steel sets before you reassemble. A worn forward drum is replaced as an assembly with the loaded TH400 forward drum.
| Brand / Part No. | TCI 228600 |
| Fits | GM TH400 (3L80), 1966-1991 |
| Includes | Oil seals, sealing rings, front and rear seals, pan and valve body gaskets |
| Does not include | Frictions, steels, bands, bushings, filter |
| Kit type | Soft-parts overhaul (wear parts only) |
Doing this repair right usually means replacing these at the same time. Same transmission, ships together.
TCI lists it for the 1966-1991 GM TH400 (Turbo 400 / 3L80). For a 1964-1965 unit or a special application, send us the year, vehicle and VIN so we can confirm it.
The soft parts for an overhaul: oil seals, sealing rings, gaskets, the front pump and rear seals, and a set of valve body gaskets, per TCI.
No. Frictions, steel plates, bands, a filter and hard parts are not part of this kit. Order those separately if your teardown shows burnt plates, a glazed band or a damaged pump.
If the clutch plates and bands measure good and the slip comes from leaking seals or rings, yes. If the frictions are burnt or the steels are blued, replace them too or the slip will return.
Use Dexron-type ATF. GM specifies 12 lb-ft on the pan bolts and 15-20 lb-ft on the pump-to-case bolts with new bolt seals.
