“Harley Klentz owns a Corvette,” wrote Hot Rod magazine’s Bob Pendergast back in the May 1960 issue, “and like all ‘true believers’ who own Corvettes, he runs it at the drags. When Harley discovered that a gear suitable for drags is not a gear suitable for the highway, inspiration occurred.”
What Klentz was inspired to do was bring an old-fashioned hot-rodding idea to late-model cars: the quick-change rearend.
When rodding was in its infancy in the days after World War II, a man named Ted Halibrand modified early Ford rear-axle assemblies (since almost all hot rods then were Fords) with a pair of extra spur gears. These gears were readily accessible at the back of a modified rearend housing, and by varying their size—the tooth count—a racer could fine-tune his axle ratio to suit track conditions without having to touch the ring-and-pinion. As often happened with cars that served double duty as both transportation and race car, a rodder could drive on the highway to a dragstrip or dry lake with the spur gears set up for a tall rearend ratio, then swap the position of the gears at the track to shorten the ratio for better acceleration.
The concept had merit for more-modern cars like Klentz’s Vette, but there was a hitch: Because they were intended for early Fords, the original quick-change rearends were hung on the Ford’s transverse leaf-spring pack and accepted the old-fashioned torque-tube driveline. They were not made for the Hotchkiss rearend style of parallel leaf spring packs and an open, U-joint-equipped driveshaft.
Undaunted, Klentz developed a quick-change that bolted to a conventional Hotchkiss-style axle housing. “Now, anyone who has slid a creeper under a Corvette knows how crowded things get immediately behind the rearend,” Pendergast wrote, “what with the design of the frame and body being what it is, so Harley made his quick-change with the spur gears up front.” Yes, that necessitated shortening the driveshaft by 2 or so inches, but once the initial work was done and the unit was installed, changing ratios was a breeze, he said. “The hardest part of the whole job is jacking up the car—after you once slide under, you should be able to disconnect the rear U-joint, remove the change plate, and swap gears with the whole job buttoned back up and ready to roar in not over 10 minutes.”
With the new rearend, “you may now head out for the nearest dragstrip to try out your new ‘wings,’ which is exactly the way your Corvette should feel if you selected the correct ratio spur gears,” Pendergast said. Building on a Ford 3.78 ring-and-pinion ratio, the Klentz Quick-Change—available through the Moon Equipment Company—offered spur-gear sets to go as tall as 1.94:1 and as short as 7.35:1.