Some of the best times we spend in our personalized trucks is when we are on the open highway with the windows down and we’re cruising. If you are like us, then you’re not big fans of cruising the downtown sports at lower speeds, but are more inclined to hit the highway. For the sake of your engine, an overdrive transmission may be just what you need. 

Our old 350 Chevy-powered ’47 International was running a three-speed 350 Turbo trans with 4.11 gears, which, as you know, is not a great combination for this type of highway cruising. It is fine, however, for those who absolutely love in-town, short-?distance, stop-and-go cruising, as it does prove great low-speed throttle response. On the highway, however, it spins up the engine and uses more fuel.

We decided that after having our low-speed fun, we were using too much fuel and weren’t comfortable listening to the whine of the small block as we approached 70 mph. It was time to make a change. We looked around for a number of answers and talked to many classic truck owners who had either installed a new set of gears, an overdrive trans or a Gear Vendors overdrive/underdrive unit. We figured that the new 700R4 trans best fit our application budgetwise, although future plans may call for a Gear Vendors unit, as it represents the best of both worlds. But we first wanted to start with a newer, more modern trans.

We selected a freshly rebuilt 700R4 from a transmission shop, along with a new lockup converter. Lokar supplied the new shifter, kickdown cable and dipstick, while the lockup harness came from Ron Francis. The Ron Francis lockup kit is preprogrammed to lock up the converter at 43 mph, and it is adjustable, allowing the lockup to be adjusted per application. This would have enabled us to retain our 4.11 gears for quicker starts and, when at speed, the converter would lock up and the overdrive would kick in, dropping the engine rpm. We like the outcome, but we can do more with the Gear Vendors unit, so we’ll be saving up for that possible inclusion.

While we thought that modifying our floorboard would be the worst of the install, it may not be needed on your particular application. The complete install took us a few afternoons, as the driveshaft needed replacing. Simple hand tools are all that is needed, and a lift and transmission jack will also make the swap much easier to do. Once the trans swap was completed we noticed a significant change, as the rpm went from 3,000 to 1,900 at around 60 mph. The entire cost of the upgrade was around two grand, and it has already saved us a ton in fuel costs, not to mention the wear and tear on the motor. Depending on how much you drive, the savings can be substantial.

After completing the installation and making a few minor adjustments, we were cruising at much lower rpm, which also resulted in lower engine operating temps and less exhaust and engine noise. We noticed an initial seven-mpg gain in fuel economy right off the bat, and much smoother cruising. Read along as we swap our 350 Turbo for a 700R4.