Another is the heavier-duty...
Another is the heavier-duty roller clutch.
THM 700-R4
The next GM overdrive unit, which came out for '82 models, was the THM 700-R4 (3.06 First, 1.63 Second, 1.00 Third, and 0.070 Fourth) and was loosely based on the THM 350, with most of the design work done by the Chevrolet Division. Its original intended use was in light-duty trucks. Unlike the THM 200-4R, this model was designed from scratch as an overdrive transmission and didn't require the installation of a third planetary unit. The major components of the THM 700-R4 were a vane-type oil pump, a 2-4 band assembly, five multiple-disc clutches, two planetary-gear sets, a sprag clutch, a roller clutch, and the traditional valvebody assembly.
4L60/4L60-E/4L65-E/4L70-E
For the '90 model year, the 700-R4 was renamed 4L60 and it was used until '92. The new GM transmission identification code is deciphered as:
4-four-speed;
L-longitudinal installation (RWD);
(T-transverse installation (FWD));
XX-torque rating as assigned by GM Powertrain;
E-electronic controls instead of a conventional valvebody, beginning in '93.
The torque converter is an...
The torque converter is an advanced design that is able to better control stall speed, while mechanically locking during highway operation.
With advancements in electronics, it wasn't long until the transmission was integrated into the engine controller. It was realized that many functions controlled through the valvebody could be better tuned via solenoids. Thus, the traditional valves that gave the valvebody its name were replaced by fast-acting electric solenoids. Hydraulic pressure was still at work, but instead of overcoming spring pressure in mechanical valves, the solenoids directed fluid flow when commanded by the ECM/PCM. The integration of electronic controls changed the name of the 4L60 (which was known internally in GM as the MD8), to the 4L60-E, for '93.
A variation called the 4L65-E featured a five-pinion planetary-gear set in place of the 4L60-E's four-pinion, and a stronger output shaft, making it heavier duty. It was introduced for the '01. The 4L70-E followed and was stronger yet.
4L80-E
The 4L80-E was based on the THM 400 three-speed (later called the 3L80) and debuted for '90 or '91. It used six bolts in the bellhousing case and a four-pinion planetary gear set.
By '02, the 4L80-E had been in production for 11 years and was due for upgrades, so it received a heavier-duty overdrive roller clutch. GM states: "This modification incorporates larger-diameter rollers and a 'shuttle-car' design, which allows the high-speed 4-2 downshift maneuver without downshift-sequencing delays. This design also incorporates error-proof assembly features and maintains the roller position in the clutch assembly."
Another upgrade was an induction-hardened and shot-peened turbine shaft for increased durability. GM explains: "The turbine shaft transfers torque from the engine via the torque converter to the gear sets. The turbine shaft is now hardened by electrical heat-treating and then shot-peened to relieve internal stresses in the metal. This sequence of processes increases the strength of the shaft, for increased durability." The torque rating of the 4L80-E was 440 lb-ft, and the transmission was used through '06 in some truck applications.
A variation called the 4L65-E...
A variation called the 4L65-E featured a five-pinion planetary-gear set in place of the 4L60-E's four-pinion, and a stronger output shaft, making it heavier duty. It was introduced for the '01. The 4L70-E followed and was stronger yet.
4L85-E
In '02, the 4L85-E was born of the need to hold even more torque. It featured beefier internal parts, along with a five-pinion planetary design. This allowed for less stress on the gear-train during high-torque input.
The 4L85-E was also originally designed as a truck transmission, and was offered with three different bellhousing configurations and minor internal tweaks to make the unit application-specific. The latest versions use a bellhousing with seven bolt holes to further expand the installation appeal.
Torque-converter upgrades increase durability. According to GM, "The torque converter input and output pump blades, where torque is transferred via fluid, are brazed to the torque converter input and output shells."