TH400 3L80 Master Overhaul Rebuild Kit, Clutches & Steels

This is the full master overhaul package for the GM Turbo Hydra-Matic 400, the TH400 (also badged 3L80 in later trucks). It is the kit you pull off the shelf when the unit is coming all the way apart on the bench and you want every friction and sealing part new before it goes back behind the engine. It covers the 1965-and-up TH400 family used behind big-block Chevy, Pontiac, Olds, Buick, and GMC applications, and it is a common swap-in for street rods and race builds because the case is nearly indestructible once the clutches and seals are fresh.

Inside you get the friction clutch plates, the matching steel plates, the molded pistons, the gasket set, and the complete run of lip seals, sealing rings, and O-rings the transmission needs to be put back together. That is the difference between a master kit and a plain gasket-and-seal reseal: the reseal only stops leaks, while this replaces the wear items that actually carry torque through the direct, forward, and intermediate clutch packs.

On the bench, the frictions and steels stack into the clutch drums to spec, the new pistons replace the old bonded pistons that harden and crack with heat and age, and the gaskets and seals go in as the pump, center support, and tailhousing are torqued back down. Rebuilding the TH400 in one boxed kit keeps the clutch clearances and the seal set matched instead of ordering hard parts piecemeal in the middle of the job.