GM’s 4T80-E transmission primarily used in Cadillac vehicles along with the Aurora, Bonneville and Lucerne vehicles, develop left side axle seal leaks (figure 1). This is typically caused by a worn output shaft bushing in the 3rd clutch drum. When this bushing wears, the axle being spline to the output shaft is no longer supported causing damage to the seal. Removing the right side differential assembly and output shaft will allow a tech to pull the left axle and replace this bushing and axel seal without transmission disassembly.
Similarly, GM’s 6T40 transmission also develops a left side axle seal leak due to bushing wear. The difference here is that this bushing is pressed into the case (figures 2, 3 and 4), making it difficult to change with disassembling the transmission.
There is an aftermarket tool kit available from Superior Transmission Parts that turns this job into a simple in car repair. The kit comes with a bushing removal (figure 5) and indexed installation tool that allows the technician to remove the damaged bushing with the transmission in the vehicle. They also provide a replacement axle seal and bushing that is wider for better support and is Teflon® coated for improved durability (figure 6).
Ford’s version of this transmission called the 6F35 suffers from this left side axle leak for the same reason. The same tool kit, seal and bushing will offer an in-car repair here as well.
Do not overlook inspecting the condition of the bushing journal area on the axle’s stubby shaft for damage, especially if the bushing was found to be severely worn.
