TH400 3L80 Master Rebuild Kit, Turbo 400, 1965-Up

The TH400, also stamped 3L80, is GM's Turbo-Hydramatic 400 three-speed automatic. This master kit carries the wear parts you replace on a full teardown: the clutch frictions and steel plates for each pack, the complete gasket and rubber seal set, the sealing rings, and the pan filter. It covers TH400 units built from 1965 up.

Fits the Turbo 400 behind small- and big-block Chevy, Buick, Oldsmobile, Pontiac and Cadillac engines, plus the same case used in GMC and Chevrolet trucks and swap builds. It is the same three-speed core sometimes called out as TH475 in heavy-duty applications.

On the bench you strip the unit to the bare case, wash every part, then reassemble with new frictions and steels stacked in each clutch pack, fresh sealing rings on the drums and center support, and new gaskets and lip seals at the pump and servo. Soak the frictions in ATF before install and check clutch pack clearance as you build.

Reach for this when a TH400 slips in a gear, flares on the 2-3 shift, or leaves friction material in the pan: the signs the clutches and seals are worn out. It restores holding capacity and clean shifts in one kit instead of chasing down each seal and plate separately.