Wear at the direct clutch drum bore in GM TH400, 4L80-E and 4L85-E transmissions allows 3rd and Reverse apply oil to exhaust. This oil leakage can result in direct clutch failure, delayed or no 3rd/Reverse, slips in 3rd or no 4th Gear, and the various slip codes noted above. Often the direct drum bore is worn beyond the ability for new seals to restore the hydraulic integrity.

Sonnax direct drum sleeve kit 34838-01K salvages worn direct clutch drum bores and restores the hydraulic integrity at the center support piston ring locations. Machining of the direct drum is required.