Zack Farah: "Heat is arguably the biggest detriment to transmission longevity. Excessive heat in transmissions is detrimental for the same reason as in an engine. Would you hang your engine's radiator off the bottom side framerail of your car? Of course not. With proper cooling, a performance transmission should live for the long haul. Automatic transmission fluid serves many functions in a transmission. It's a hydraulic medium to transmit pressure, sometimes reaching in excess of 250 psi, to apply the clutch packs. Another one of its functions is to transfer torque and horsepower through the torque converter, and this is where 90 percent of heat is generated in the transmission. This is also why ample cooling and airflow over the cooler is necessary. The torque converter is in a constant bleed-and-feed mode. It's constantly recharging with sump fluid and is building heat in the converter. The fluid is then pushed out to the cooler where it must receive adequate cooling and return to the transmission, where it charges the lubrication circuit. This return fluid must lubricate all bearings, bushings, thrust washers, planetary gearsets, clutch packs, lip seals, sealing rings, and the valvebody assembly. After all this fluid has returned to the sump, it goes back to the torque converter and must still be cool enough to allow the converter to transmit torque, and then the cycle repeats. We recommend and insist that a 20,000 GVW Hayden cooler is installed with any transmission up to 400 horsepower, and a 30,000 GVW unit is required for any application above 400 horsepower. We also recommend eliminating any coolers that are integrated into the radiator core, as these are notorious for failure."
Stanley Poff: "Heat is the enemy of transmission performance and durability for multiple reasons. First off, it can break the transmission fluid down to a point where it will no longer perform. When this happens, it is usually a sign that the converter stall speed will go way higher than normal. Secondly, there are rubber seals and O-rings in the transmission that will actually melt or become disfigured to a point where they won't seal any longer. This is why it's imperative to always run a sufficient transmission cooler."
Regis Finn: "Installing an adequate transmission cooler increases the longevity of a transmission. Proper fluid temperature is the key to component longevity. When modifying a transmission to operate near peak potential, it is vital to keep [the] lubricant working at its peak performance as well. Heat deteriorates the performance of the parts. For instance, parts can become glazed due to oil breakdown, and seals can become hard and brittle, causing slippage. Choosing the right cooler for your transmission will depend on vehicle type and intended use. If the application is racing, heavy towing, or you live in a hot and dry area, you may need to use a larger cooler. If you're only using a car for street/strip duty, short-distance driving, or mild towing then you may be able to install a smaller cooler."
Stanley Poff: "In a manual transmission, gears slide along shafts as you move the shift lever from one position to another. In an automatic transmission, however, the gears are never physically moved and are always engaged to the same gears. This is accomplished through the use of planetary gearsets.