Our LS-Powered C10 Goes Into Overdrive With Gearstar’s Bulletproof 4L60E

September 5, 2024

01 Gearstar Performance Transmission facility is so clean — Zach Farah’s Gearstar Performance Transmission facility is so clean anyone’s mother would be proud. The handpicked staff is made up of experienced professionals and all parts are USA sourced.

When overdrive automatics came on the scene they found their way into a variety of modified vehicles, and for good reason. These transmissions were tough, had a wide gear ratio spread with a low First gear and an overdrive Fourth. In addition there was a lockup torque converter that provided a direct connection from the engine to the rearend. But if there was any shortcoming to the 700-R4 it was the throttle valve (T.V.) cable (sometimes called the kickdown cable).

02 thoroughly clean and inspect the transmission cases — The first step in the building process is to thoroughly clean and inspect the transmission cases. Any that are not perfect are tossed out.

Ironically, the problem with the 700-R4 T.V. cable was often a result of the induction system being used. The T.V. cable controlled the hydraulic pressure in the transmission and in stock configuration the GM carburetors and fuel injection systems had the correct ratio as the throttle was opened to activate the T.V. cable appropriately. Unfortunately, many aftermarket carburetors and fuel injection systems did not have levers with the proper ratio and the result was low hydraulic pressure at some throttle settings that allowed the clutches to slip, which ultimately led to a complete transmission failure.

03 Each Gearstar transmission is built by one master technician from start to finish — Each Gearstar transmission is built by one master technician from start to finish. Should a customer have questions or concerns about their new purchase, the person who built that transmission will be available on the Gearstar tech line.

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For over two decades Zach Farah’s Gearstar Performance Transmission has specialized in building what they describe as: “The best horsepower transferring systems available.” At the outset of their popularity, Farah recognized the problems associated with 700-R4 transmissions and had the cure, quickly establishing Gearstar’s reputation for bulletproof overdrives. That same reputation continues today in a product line that includes 200-4R, 700-R4, 4L60E, 4L65E, 4L70E, 4L80E, 4L85E, as well as the six-speed 6L80E and 6L90.

04 Gearstar has a long list of upgraded parts for performance applications — Gearstar has a long list of upgraded parts for performance applications. On the left is an OE sun shell that uses a thrust washer, on the right is a Gearstar high-performance reinforced replacement that uses a thrust bearing.

For our project C10 pickup we chose one of the most popular GM overdrive transmissions available, the 4L60E (that’s GM speak for a four-speed, longitudinally positioned, 6000 GVW, electronically controlled transmission). Basically this transmission is an improved version of the venerable 700-R4. The gear ratios are the same: First 3.06, Second 1.62, Third 1.00, Fourth 0.70, and a lock-up torque converter is used. The big differences are the T.V. cable is gone and the shift valves are operated by electric solenoids, all controlled by an ECU (electronic control unit).

05 this is the sun shell as installed in the case the rear planetary gearset fits inside and engages the internal teeth — For reference this is the sun shell as installed in the case, the rear planetary gearset fits inside and engages the internal teeth.

Although the 6L80E is a great transmission, there were a few peculiarities that Gearstar has addressed. As Gearstar’s sales manager, Ryan Steele, explains it, “GM uses transmission cooler bypass thermostats in many but not all models (trucks did not start using them until 2014). The reason for this is to heat up the transmission quickly to improve fuel economy. It is not advised to use thermostats in high-performance transmissions because they run hotter (mainly from the higher stall converter). Gearstar uses thermostat bypass kits in all their transmissions. The other issue with these transmissions was the torque converter friction materials. Starting in 1996, GM introduced the EC3 lockup in the 4L60E, which allows partial lockup apply to improve fuel economy. Most GM transmissions made after 1996 have some form of partial lockup apply (the only exception is the 4L80E, being GM’s workhorse transmission). Of course, this required GM to develop a friction material that could withstand being constantly slipped, hence the development of the woven carbon converter lockup friction. There are two main issues regarding this friction. One, it is only 0.025-inch thick, and two it easily glazes if the slip becomes excessive. As the TCC regulator valve wears, the lockup pressure drops and the friction slips more than normal. Once this happens, the friction glazes and the converter develops a clutch shudder; each time it shudders it wears off a bit of the material. With the friction being only 0.025-inch thick when new, you can see why it won’t be long before the friction is totally disintegrated. Once the friction is gone the shudder will disappear but with the piston now running metal to metal with the cover it is generating a massive amount of metal particles that will get into the solenoids and valves and transmission failure is imminent. All Gearstar transmissions have the EC3 system removed and full lockup restored.”

06 on the right is a hardened five pinion upgrade — On the left is an OE rear planet assembly with four-pinion gears, on the right is a hardened five-pinion upgrade.

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When it comes to selecting a Gearstar 4L60E Steele stresses that there is no “one size fits all transmission.” The team will want to know the specific application (street, race, or a combination) power range, gear ratio, tire size, vehicle weight, and so on to determine what stall speed converter is appropriate and what transmission upgrades are necessary. Transmission are identified as level 1, 2, 3, or 4, or from “stock applications” up to 650 hp and 600 lb-ft of torque.

07 the input drum on the right has an added reinforcement for strength — Another performance upgrade, the input drum on the right has an added reinforcement for strength (arrow).

Gearstar recommends and includes an external transmission cooler with all of transmissions. The transmission cooler should be mounted in the front of the vehicle to ensure that it is getting proper airflow for cooling. The normal operating temperature should be between 170-180 degrees. If needed, an electric fan can be added to the cooler to help maintain the temperature.

08 Gearstar offers an upgraded front planet pinion assembly with a hardened five pinion replacement — Like the rear assembly, Gearstar offers an upgraded front planet pinion assembly with a hardened five-pinion replacement.

For a long life, it’s recommended that servicing is done every other year or 15,000 miles. If you are towing a lot, or driving the car very hard, it’s recommended servicing the transmission once a year. However, never flush the transmission. The proper service would be to drop the pan and allow the fluid to drain, replace the filter, and refill the transmission. Follow those guidelines and you and Gearstar will be happy for lots and lots of miles.