Any time one runs across a custom classic truck that has been in the hands of the same owner for many years, it is always interesting to note the changes both the owner and the truck have undergone. It seems the more radical the truck was built in the beginning, the less the owner tends to enjoy it as he ages, and almost without exception the truck is driven less.
Such was the case for Jerry Sievers of Placentia, California, and the '64 Chevy shortbed Stepside pickup he has owned for the last 30 years. Complementing the '64's classic hot rod looks, the drivetrain in Jerry's pickup is a 327 with three deuces backed by an M-21 Muncie four-speed hooked to a set of deep 4.10:1 gears. As we all know, deep gears are a lot of fun when it's time to leave someone sitting at the stoplight, but the fun starts to wear off as soon as one hits fourth gear and the engine is still screaming like a banshee. In addition to the wear and tear on both the engine's internal components and the driver's nerves, an engine sustained at higher rpm burns a lot more gasoline and ultimately wears out faster.
Jerry considered dumping his four-gear Muncie in favor of a late-model five-speed, but in addition to losing a major part of his '64's nostalgic appeal, he was concerned installing a five-speed with its wider ratios would hurt his truck's performance. A standard five-speed would drop the rpm by 40 percent on a first to second gear shift, which means when winding first to 4,000 rpm and then shifting to second, the tach would drop to 2,400 rpm. To give an example of how wide a jump that is, skip-shifting an M-21 Muncie from 4,000 rpm in first to third gear will drop the tachometer to 2,327 rpm.
Before Jerry installed the Gear Vendors Under/Overdrive unit, the jump from 4,000 rpm in first gear in his close-ratio M-21 Muncie would be to 2,981 rpm in second gear. After installing the Gear Vendors Under/Overdrive unit, shifting from first gear at 4,000 rpm to first gear overdrive will drop the rpm to 3,120. When we asked Gear Vendors about the effect of a clutchless power shift from first gear to first gear overdrive, they explained, "Since the vehicle actually is gaining speed during the Gear Vendors shift (no clutch depression), you actually would never see less than probably 3,300 rpm."
Prior to installing the Gear Vendors Under/Overdrive unit in Jerry's '64, he was aware of the benefits he would reap with a taller top gear as far as engine noise and better gas mileage, but it was being able to select closer-ratio gears that really blew his mind.
Listening to Jerry's '64 Chevy as he sped away, the truck sounded like a dragster blasting through the gears at the dragstrip. This was due to the ultra-close gear ratios created by the Gear Vendors Under/Overdrive unit splitting the M-21 Muncie's stock ratios, plus its ability to withstand full-throttle power shifts. For example, the Muncie's 2.20 first gear becomes 1.71 with the Gear Vendors unit engaged, in comparison to shifting to the close-ratio Muncie second-gear ratio of 1.64 (which, thanks to Gear Vendors, no longer seems as close as it once was). For the next shift, since second-gear overdrive and third-gear direct both have a 1.28 ratio, the hot setup is to manually shift into third gear direct and then punch the Gear Vendors button for a clutchless shift to third overdrive, which is 1.00, the same as the Muncie's fourth gear. And now, of course, since we are back into fourth gear, where the final drive on Jerry's '64 is 4.10:1, his little 327 is turning some major rpm at highway speeds. This is where the Gear Vendors unit, with its 28.6 percent faster overdrive cruising, really comes into play. The 4.10:1 differential in Jerry's '64 in essence becomes a rearend packing 3.20:1 gears.
In comparison to a major manufacturer's mass-produced transmission manufactured with larger allowable tolerances and corners cut to save costs, the Gear Vendors Under/Overdrive unit is a precision-made jewel. Starting with the overdrive's cases sourced from foundries in Germany, England, and California, Gear Vendors custom-machines their internal parts in-house at their El Cajon, California, manufacturing plant. Gear Vendors precision-cuts their splines instead of rolling them. In conjunction with Gear Vendors' improved design of the legendary Laycock de Normanville's planetary gear arrangement and specially formulated friction materials from Raybestos, the Gear Vendors Under/Overdrive unit is capable of handling 1,200-plus horsepower. So it doesn't matter if you use a Gear Vendors Under/Overdrive unit for racing or just beat it as hard as you can on the street, they are unconditionally guaranteed for two years and are designed to last a lifetime.
Installing the Gear Vendors Under/Overdrive unit onto the M-21 Muncie is pretty straightforward and doesn't require any special skills. Since there are only four bolts that hold a Muncie in place, it was easiest to remove it and install the Gear Vendors unit on the workbench.
Thanks to keeping the 327 within its power curve, the '64 accelerated faster and was more tractable on the freeway, switching out of overdrive to function as a passing gear, then back to overdrive for better gas mileage. CCT
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Here are three Gear Vendors Under/Overdrive units with optional deep-sump pans thoroughly tested and ready to be packed for shipping to anywhere in the world. Deep sumps are used for large truck applications. | 
Thanks to Gear Vendors machining components in-house and tight quality control, parts like this only require a thin gasket without any sealants. |
These lengths of special steel round stock will be cut to size and then have splines cut in. | 
After the transmission was removed from the truck, the next step was to remove the stock M-21 Muncie's tailshaft. | 
With the stock tailshaft removed, Guillermo prepped the Muncie's case by scraping off the old gasket and installing the new gasket dry. |