4L80E Transmission Overhaul Gasket and Seal Kit

This is the sealing half of a 4L80E overhaul: the case and pump gaskets, rubber lip seals, O-rings, and sealing rings that get replaced any time the unit comes apart. It is a WIT (Whatever It Takes Transmission Parts) kit and it crosses to interchange numbers W34002EA, KP34900FX, and 80000733. It does not contain frictions, steels, bushings, or a filter - this is the soft sealing package only, which is what you want when the clutch pack is still serviceable or you are buying your frictions separately.

Fitment is the 1997-2011 GM 4L80E and 4L85E. That covers Chevrolet Silverado 2500 and 3500, Suburban, and Express, GMC Sierra, Yukon, and Savana, plus Cadillac, Hummer, Workhorse chassis, and the commercial and motorhome applications running the same heavy-duty four-speed. The 1991-1996 4L80E uses different sealing parts, so check your build year before ordering - a 90-96 unit needs the earlier kit, not this one.

On the bench this is what you lay out first. Every lip seal that came out of the drums and servo bores gets replaced, the pump O-ring goes on before the pump drops back in the case, and the sealing rings go on the shafts and center support before anything stacks up. Reusing old rubber is the single most common reason a fresh rebuild comes back - heat cycling takes the set out of a lip seal, and it will bypass under load even though it looks fine laid on the bench.

The failures this fixes are pressure failures, not mechanical ones: delayed engagement into drive or reverse, a slip that only shows up when the trans is hot, a soft or flaring shift, and fluid weeping past the servo covers and pan rail. Those are hardened seals bleeding off apply pressure, and no amount of valve body work corrects it until the rubber is new.