TH400 Transmission Oil Pan with Drain Plug and Gasket

A replacement transmission oil pan for the GM Turbo Hydra-Matic 400 (TH400, also sold as the 3L80) at the stock 2-1/4 inch depth. It is a finned black pan with a drain plug already fitted, and it comes with a pan gasket and a set of pan bolts and washers. It crosses to OE-style reference number SP8593BK.

Because it keeps the factory depth, it bolts up under the stock TH400 filter and pickup without a spacer or a deep-pan filter, and it will not hang any lower than the original pan. That matters on lowered cars and on trucks and street rods where the stock pan already sits close to the crossmember or exhaust.

The main reason to swap one on is the drain plug. A factory TH400 pan has none, so every fluid change means loosening the pan and letting ATF pour over the edge. With a plug you can drain it hot, check what comes out for clutch material and metal, and refill without breaking the gasket seal. It is also the fix for a pan that has been bent from a jack or road debris and weeps at the rail no matter how many gaskets go on it.

On install, clean the case rail of old gasket and sealant, set the gasket dry, and snug the bolts in a cross pattern to the light factory torque rather than cranking them down, which is what distorts pan rails and starts leaks. Refill with Dexron-type ATF and check the level hot in park.