Auto Basics
Zack Farah: "Automatic transmissions are extremely complex devices comprised of dozens of components. In trying to explain how they work, a good place to start is the trans pump, which supplies hydraulic pressure to charge the torque converter and cooling and lubrication circuit, to apply clutch packs, band apply servos, and valvebody control systems. The input clutch drum and input shaft transmit torque from the engine and torque converter to the input element of the planetary gear system. The clutch packs provide a release mechanism for Neutral and Reverse. The direct clutch pack contains the Third gear clutch and houses the intermediate clutch sprag, providing control over the planetary sun gear. They determine whether it will be held for Second gear engagement, driven for Third gear, or serve as reverse input for Reverse engagement. The planetary gearsets consist of two planetary gearsets. The output planetary carrier is linked to the output shaft. The reaction planetary carrier is linked to the low-reverse clutch pack. The reaction planetary is only engaged in Low gear and Reverse, and otherwise it just goes around for the ride. The input sun gear is splined to the forward clutch pack and is applied in all forward gears. The intermediate clutch is engaged in Second gear, but is ineffective for engine braking. Hence, an intermediate brake band is applied in manual Second by a servo for engine braking in Second gear. Finally, the valvebody is basically a hydraulic computer and generates logic for shift patterns via balance valves."

Dyno Testing
Zack Farah: "At Gearstar, we dyno test every transmission that we build. The importance of testing each transmission is to verify operating pressures, shift points, and overall functionality. The transmission dyno is an indispensible tool for R&D since it facilitates quick removal of the pan and valvebody for recalibration of the valvebody, governor, and shift solenoids. The fluid recovery system on the dyno makes quick and easy work of dealing with 10 quarts of hot transmission fluid. Simulated loads are achieved via an 800-pound flywheel which replicates the inertia of a vehicle weighing 3,000 pounds with a 3.73:1 rear axle ratio. By running a transmission on a dyno we can check for leaks, vibrations, and abnormal noises during a simulated road test. The transmission is observed for leaks at the pump, front seal, speedo housing, rear seal, servo, and accumulator housings. Shift points and shift firmness specifics for each custom-built Gearstar unit are verified on the dyno as well. Any variations in shift timing or shift quality are readily accessible for recalibration on the transmission dyno. For instance, if we experience one shift point which does not occur at the same load-speed setting as the others for that shift calibration package, it's addressed, corrected, and verified upon retest. Transmissions which are shifted via computer or ECM, such as 4L65E and 4L85E, are tested for up to 90 minutes or 120 miles to verify that shift solenoids and pressure force motors will remain functioning properly over the long haul."

Achilles Thomas: "The purpose of dyno testing a transmission is to check that it's working properly, and to watch for leaks and excessive noise. Whether this step is mandatory is up to the trans builder. Monster Transmission actually takes testing a step further and installs each transmission into a test vehicle to drive it either on the street or on our state-of-the-art chassis dyno. By giving our transmissions a real world testing experience, we can fully customize the way the transmission performs and make sure it's working before it leaves our facility."