While mechanical reliability is subjective and depends heavily on proper maintenance and application, several units have achieved legendary status for longevity. Examples include the legendary GM Turbo-Hydramatic 400 (TH400), later generations of the Allison 1000 series automatic transmission, and robust manual gearboxes like the ZF S5-42, all of which are widely celebrated by mechanics and fleet operators for their ability to withstand hundreds of thousands of miles of heavy-duty abuse.