High Performance Transmission - Transformation

Standard equipment in the F-car and a slew of other V-8-powered GM vehicles, the Hydramatic 4L60-E four-speed automatic transmission is a capable performer-to a point.

With a maximum engine torque capacity of 360 ft-lb, the "L60," as GM engineers call it, is best suited to moderate performance applications. Recently a new, stronger version of the L60 has quietly appeared. It's the 4L65-E and it has been attached to 6.0L versions of the Gen. III V-8 found in half-ton trucks, like the Cadillac Escalade AWD. In these vehicles, the "L65" has an engine torque rating of 380 ft-lb.

In the last year or so, an automotive application of the L65 was tuned for the high-performance HSV vehicles of GM's Australian Holden unit. These are rear-drive, LS1-powered cars, including the Holden Monaro coupe, which is being morphed into the '04 Pontiac GTO.

Besides the higher torque rating, the L65 is simply built tougher than the L60. In fact, in automotive applications, the L65's torque rating is closer to 400 ft-lb. "The L65 is stronger all around," says Steve Ford, GM's assistant chief engineer for the 4L60 and 4L80. "Although it was initially built for truck applications, the gearing we've developed for automotive duty cycles makes it a great performance upgrade. Right out of the box, it can handle about 20 percent more torque than the L60."

GM Performance Parts has released the 4L65-E as an over-the-counter item (PN 24221888), hoping to lure enthusiasts with older vehicles to the benefits of the electronically controlled overdrive transmission, as well as offering modern performance enthusiasts a stronger alternative to the stock 4L60-E. In a nutshell, the L65 differs from the 4L60-E in these ways:

* Five-pinion gears for input and reaction gearsets (versus four-pinion gears in the L60)* Heat-treated stator shaft splines* Induction hardened turbine shaft* Heavier-duty Low/Reverse roller clutch* Additional friction plate added to 3-4 clutch(seven plates versus six in L60)* Shot-peened output shaft* Revised valvebody calibration.

The use of five pinion gears for the input and reaction gearsets spreads the torque load so that less is held by any one gear. L65's gears also are made of powdered metal, which GM claims allows for more precise detail and accuracy of the part, as well as higher overall strength. (In these GM transmissions, the input and reaction gearsets are comprised of a sun gear, planetary gears and a ring gear.)

Additionally, a heavy-duty, needle-type thrust bearing replaces a thrust washer for the interface between the reaction shaft and the reaction sun gear and shell.

Increasing the strength of the stator shaft came from heat treating the shaft's splines (which mesh with the hub of the stator roller clutch), and substituting the L60's steel-backed bronze bushings with stronger aluminum versions.

Also in the L65, the turbine shaft (the main component transferring torque from the converter into the transmission) is strengthened through induction hardening. Compared to heat treating, which involves a heating/cooling cycle to improve hardness and strength, induction hardening utilizes an electric current in the heating/cooling cycles.

"The premium parts specified for the L65 are similar to parts you'd find in aftermarket performance build-ups," says Ford. "They were included for durability and the transmission's performance design."

Another improvement specific to the L65 is the use of larger-diameter rollers in the roller clutch. They better handle the increased loads of the L65, as do the seven friction plates of the 3-4 clutch. The L60 has only six friction plates for the 3-4 clutch; adding a seventh plate creates higher shift energy capacity.

Hydramatic engineers also improved the output shaft's capacity through shot-peening. The process involves concentrating the peening in several high-stress areas of the output shaft, thereby producing a longer fatigue life.