Those of you who drive older trucks might wonder about the magic that apparently gives newer rigs the ability to produce such impressive fuel-economy figures. You may know that newer trucks tend to have smaller engines than the older ones, and that these smaller engines are more efficient, are fed by carefully controlled fuel-injection systems, and that those engines push bodywork that is much more aerodynamic than ever before. In addition, new trucks roll on tires with less rolling resistance than was possible with older-generation tires. But theres one more thing that by itself is as important as all those other elements: Newer trucks have overdrive transmissions.
Overdrive is the single most important weapon in your miles-per-gallon arsenal. Its also very important when it comes to reducing the wear and tear on your trucks engine. Obviously, an engine that turns fewer rpm lasts longer. Almost all new vehicles offer an overdrive tranny as standard equipment. The automakers know that by equipping cars and trucks with overdrive, they can meet stringent, federally-mandated Corporate Average Fuel Economy (CAFE) standards. Also, because overdrive contributes to engine longevity, they can extend factory warranty periods with little or no chance that youll be dropping by the dealer for a free engine replacement.
So, what do you do if you have an older rig that does not enjoy the benefits of an overdrive? Well, besides selling it and buying a new one, you can upgrade to an overdrive. An overdrive upgrade can be done by swapping to a more modern transmission or by installing an aftermarket overdrive unit. The idea of swapping in a factory transmission might sound easy, but dont be fooled. Many modern automatics are computer-controlled, so you might need an expert to help you wire it into your truck. Also, whether you have an automatic transmission or a manual one in mind for your swap, you have to consider what it will take to mate it to your engine and T-case. Manufacturers such as Advance Adapters and Novak have most of this figured out and offer a wide range of adapters.
But there is another solution. The aftermarket overdrive makers know that they cant sell overdrive units to the masses without adapters to make them fit. So if you decide on one of these units, the aftermarket supplier you choose to work with likely will have done the work for you. Here is a list of some of the sources for overdrive units, overdrive transmissions, and adapters.