Originally Posted by Autobahn335i
What kills the trannies in the first place? Just the heat?
Stable transmission fluid temps are critical to the correct operation of the multi-plate clutch packs in the transmission.
If the transmission is running outside of its optimal temp, the clutch packs can slip or flare on gear changes, which in turn generates more heat within the tranny and exacerbates the problem.
Poor quality transmission fluid, or fluid that is beginning to break down as a result of excessive service length or heat can also cause clutch pack slippage.
However whilst stable operating temps and high quality fluid are critical to AT serviceability, they still have a torque threshold where the clutch packs will slip regardless of running temperatures or the condition of the transmission fluid.