Why does towing wear out transmissions faster?

Summary:

Jaden explains that towing wears transmissions faster because it puts more stress on the unit, and he ties that directly to why the shop builds tow transmissions the way it does. From the factory there is a small amount of slippage during shifts. Add 15,000 pounds behind the truck and that same shift now carries far more stress, so the transmission slips slightly more on every shift and wears faster as a result. That is the reasoning behind installing shift kits on heavy duty tow builds, since reducing slippage between gears addresses the problem at its source. He then describes the secondary consequence: slippage generates heat, which can overheat the transmission. He states plainly that heat kills transmissions, burning up the fluid and causing it to lose viscosity, at which point it no longer holds properly.

Answer:

Towing wears out transmissions faster because it's more stress on the transmission, which is why when we rebuild them heavy duty for towing, we do shift kits and stuff, because it's less slippage between the gears. From a factory, there's a little bit of slippage in the shifts, and when you're putting 15,000 pounds behind it, you're adding a lot of stress to it. And every time it shifts, it's going to be slipping that just a little bit more, and it's going to wear it out faster. The other thing too is that slippage will cause heat, and then sometimes you'll overheat the transmission, and heat kills transmissions. It'll burn up the fluid and lose the viscosity, and then it won't hold right. So it's really two things stacking on each other. The added weight makes every shift work harder, and the extra slipping from that added work generates heat, and once the fluid is cooked it can't do its job anymore.