Accumulator-piston wear is common and fixes are readily available, but the little pocket where the piston pin sits in the accumulator housing also wears, and this is a more-difficult problem to solve. This article describes a way to salvage accumulator housings using parts and tools you have lying around in your shop.
This particular tech call was the usual 4T60-E or 4T65-E transaxle with the code P0741, “Torque Converter Clutch System Stuck Off.” It began as so many times before with the normal question, “Was this unit just rebuilt or is it coming back with this problem?” The next question was, “What repairs have you done to correct this problem?”
When GM introduced the stamped-steel drum for the THM 200 transmission, it presented technicians with some new challenges. The 200 direct drums would crack where the inner liner (where the piston lives) was joined to the outer shell. The weld that holds the two members of the drum together is subject to pivotal flexing each time the clutch is applied. Over time, this flexing action will cause a crack at the weld.
A customer comes into your shop in a GM vehicle with a 4T60-E transmission that’s making a lot of noise no matter what speed the car is going but is quiet as long as there’s no wheel movement, or possibly no movement at all. You do the basic diagnostics, pull the pan and discover that the pan is full of metal, and upon disassembly you find the differential parking-gear bearing is blown. Or, even worse, a unit you just repaired a couple of months ago comes back with one of these problems.
The wrong differential was installed when the accident repairs were made two years before. The problem never surfaced until the car was driven more than 30 miles at one time. Since this was a second car, it took two years for the problem to show up.