700R4 and 4L60E Forward Drum Repair - Part 1

In this video, I show you how to potential salvage a forward clutch drum that would otherwise have to be replaced due to fluid leaking under pressure at the 2-3 feed circuit.

Technical context:

Failure of the 3-4 clutch pack in 700R4s and 4L60Es (especially 4L60Es) is the number one pattern failure mode for this family of transmissions...I believe the leading direct cause to be the forward drum. Specifically, high-pressure apply circuit leaks at the base of the input shaft where it is press-fit into the drum.

Third gear feed oil is routed through the stator and 2-3 feed orifice in the input shaft where it flows directly into the 3rd clutch piston's underside cavity*. Fluid instantly fills the cavity, forcing the piston forward to compress the 3-4 clutch pack, holding it to give the vehicle 3rd gear....The 3-4 clutch pack continues to hold when the transmission upshifts to forth.

*Approximately 80% of 3rd gear apply oil is routed directly to the band release/3rd gear accumulator circuit which pushes the servo off the band to affect release. This is a timing event that happens in concert with the application of the 3rd clutch piston so a clean 'hand-off' can take place between the 2-4 band and 3-4 clutch pack while the forward clutch pack remains applied.

This pack becomes exposed to premature failure when a portion of the fluid volume that's coarsing through the input shaft's 2-3 feed begins to hemmorage into the case due to wear-driven voids between the base of the input shaft and inner diameter of the drum where the two are mated via a press fit.