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Overdrive 4L65-E Transmission - Bionic Transmission

Inside GM's Stronger, Faster 4L65-E Transmission

By Barry Kluczyk

Think of the 4L65-E transmission as the Steve Austin of GM's automatic overdrives. It looks like a standard 4L60-E, but beneath the skin, standard parts were replaced with improved components.

"We can make it stronger," said the Hydra-Matic engineers. "We have the technology."

Actually, the technology has always been there, and you many not have known, but the 4L65-E, or "L65" as GM's engineers call it, has been around for a little while, too.

Simply put, the L65 is a heavier duty version of the L60, which was the automatic found in the F-car, and currently, the Corvette and some light duty trucks. It's standard equipment in 6.0L truck applications, such as the Cadillac Escalade AWD, with an engine torque rating of 380 ft-lb (the 4L60-E's torque rating in the Corvette is 360 ft-lb).

An automotive application of the L65 was tuned recently in the high-performance HSV vehicles of GM's Australian Holden unit. These are rear-drive, LS1-powered cars, including the Holden Monaro coupe (reskinned as the new GTO), are considerably lighter than hulking Escaldades. Consequently, the car version of the L65 has a torque rating closer to 400 ft-lb, according to Steve Ford, GM's assistant chief engineer for the 4L60 and 4L80 transmissions.

"The L65 is stronger all around," says Ford. "Although it was initially developed 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 late-model Z28 and Corvette 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 valve body calibration.

The use of five-pinion gears for the input and reaction gearsets spreads the torque load so that less of the load is held by any one gear. The 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.

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.

Hydra-Matic 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.

By Barry Kluczyk
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