By Barry Kluczyk
Photography: 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.

Despite these upgrades, the L65's gearing remains the same as the L60's: 3.059 for first gear, 1.625 for second, 1.000 for third and .0696 for the overdrive.

Finally, the L65's valve body, including line pressure and shift timing, differs from the L60 by optimizing shifts based on a higher engine torque curve. Also, to withstand the higher fluid pressure of the L65, the springs in the accumulator valve are stronger than those in the L60.

Shift points for the L65 are programmed to complement the Corvette Z06 LS6 engine's powerband and, compared with the 4L60-E, the maximum shift speeds for each gear change is lowered from 6,100 rpm to 5,600 rpm.

"Although the 4L65-E was originally developed for trucks, the transmission available through GM Performance is specifically tailored to cars," says Ford. "We think it offers the best compromise to a five-speed manual. It's got great strength and the gear ratios complement a car's power-to-weight ratio."

Making it Fit
All the improvements made to the 4L60-E to make the 4L65-E are internal, so it will bolt up to any vehicle originally equipped with the 4L60-E. And since the L60/L65 transmissions are basically electronically controlled versions of the 4L60 (which was known as the 700R4 until the early '90s), they'll bolt up to most GM vehicles from the early '80s and up.

Of course, the 4L65-E requires the use of an electronic controller, whereas the non-electronic versions of the L60 or 700R4 do not. These non-electronic overdrive transmissions, however, were used in computerized applications and adapting them to carbureted, non-computer vehicles requires the use of a throttle valvespring and some "just right" adjustments to ensure proper kickdowns.

That's not the case with electronically controlled transmissions like the L65. Swapping it into an older vehicle, though, requires the use of its electronic controller. And if the swap is performed with a carbureted vehicle, an aftermarket controller kit with a specialized throttle position sensor is a must. Aftermarket vendors, such as JET Performance (www.jetchip.com) or Phoenix Transmission Products (www.phoenixtrans.com) offer such kits.

Here are a few additional transmission swap considerations:
* The two-piece case of the 4L65-E is bulkier than, say, a TH350 or TH400, which means the transmission tunnel may need massaging.
* The L65 is relatively long (approximately 3 inches shorter than a TH350), therefore a custom driveshaft may be required.
* Depending on the vehicle, a new rear crossmember may be required to mount the tail end of the transmission
* Because the L65 uses an electronic signal to indicate vehicle speed, a mechanical speedometer won't work without a signal converter, such as Abbott Enterprises' Cable X (see sidebar story).

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