Modernizing an Older Transmission with a Gear Splitter

Modernizing an Older Transmission with a Gear Splitter

Get better performance and save gas

Anybody who's ever driven a vintage vehicle has probably experienced the following problem: You'd like to settle into a nice cruise down the highway, but the low rear-end ratio, while ensuring a quicker launch off the line, keeps that big V-8 buzzing, even in top gear. At first the exhaust note sounds kind of cool, but after a while the drone can drive you batty (not to mention run up your gas bill). The answer is to install a gear splitter.

Extra Overdrive Gear

Obviously an overdrive gear would come in handy, but we're not going to recommend a late-model, 5- or 6-speed transmission. Most of the older transmissions are basically bulletproof, and you wouldn't want to lose their feel and look, which adds to the intrinsic value of the car. Why replace those good four gears for a newer trans that merely adds one gear, but doesn't shift as well, nor handle as much power and abuse?

What that means on the road is that now the car is able to go 70 mph at about same rpm as at 55 mph without overdrive.

Instead, you can install a gear splitter that adds an extra overdrive gear, which reduces the power output required to maintain driving speed in a specific range. It does so by allowing the engine to turn at a lower speed than the drive shaft, in this case at a ratio of 0.78:1, a 22 percent reduction in revolutions. What that means on the road is that now the car is able to go 70 mph at about same rpm as at 55 mph without overdrive.

Think Green

That makes it one of the greenest aftermarket accessories available, since the engine runs slower at all given speeds when the overdrive is engaged, consequently uses less fuel, and creates less pollution and fewer greenhouse gases.

The Gear Vendors can be engaged in any gear, so it actually doubles the number of ratios available in any transmission. Basically it can turn a 3-speed tranny into a close-ratio six-speed, divvying up the powerband into smaller increments. All told, a gear splitter is a modern yet essentially invisible upgrade that furnishes long-legged performance on the highway as well.

As one example, check out the Gear Vendors overdrive setup in this '67 Chrysler wagon with a 727 Torqueflite 3-speed automatic. While not exactly a common application, note that Gear Vendors offers gear splitters for all major transmission, and this specific install is virtually the same for Chrysler A, B, C, and E Bodies with a 727 Torqueflite. This particular transmission is also found in the Plymouth Fury (I through III models), Sport Fury, VIP and Suburban wagon Dodge Monaco and Polara Chrysler Newport, 300, New Yorker and Town & Country.

Clutchless Power

Besides slowing down the motor for better fuel economy and improved drivetrain durability, there's another potential benefit for vintage muscle cars, when under hard acceleration with a manual transmission. Typically when you want to show off or are trying to lay down a good run at the strip, the 1-2 shift is where the automatic guys blow on by. That's because by the time your tires hook up and you get the car driving down the lane, you immediately have to clutch and that gets the chassis all unloaded and squirrelly again.

With the Gear Vendors unit, though, you are 22 percent (or even more, depending on the gear ratios) farther down the track and all the way through the first two ratios before you have to clutch. That's where the clutchless, tire-barking shift function comes in real handy. With a Gear Vendors behind the tranny you can hit the button on the shifter before you ever leave the line (or traffic light). Then drop the clutch in 1st and the car will rev through 1st gear and then automatically (or you can hit it manually) shift to 1st-over, all without touching the clutch pedal.

Gear Vendor Kits

As for other types of muscle car transmissions, Gear Vendors makes kits to fit its planetary overdrive on a number of other makes as well. In addition to bolting right up to the Muncie M20, M21 and M22, it also goes on the BorgWarner T10, Mopar 833, and Ford Top Loader, along with a number of racing transmissions such as the Gforce GF5R, Jerico, Tex Racing, and Lenco units.

The Gear Vendors Under/Overdrives are found in a number of applications besides muscle cars, including certain types of passenger cars, diesel pickups, delivery trucks, RVs, and even modern cars such as the Callaway Corvette. The unit has been in numerous record-setting competition vehicles as well, from land speed to drag racers. So the technology is a proven and reliable approach to improving performance.

The unit consists basically of a self-contained auxiliary transmission with planetary gears like those found in modern automatic transmissions. It fits in line between the transmission and the driveline. Since the unit has a pressurized lubrication system driven by an internal pump, it doesn't share any of the fluids of the vehicle's OE components.

Upon activating the unit with a switch on the shifter or dashboard, a solenoid closes a valve, changing a path of oil to hydraulically hold a clutch pack that drives the planetary gears. These gears reduce the drive ratio 22 percent (0.78:1), so you have intermediate ratios to maintain engine rpm at the optimum level.

Installation Details

Installation of a gear splitter at Gear Vendors typically takes about a half-day or so, and is fairly simple in most applications, so it could be done by a relatively experienced home mechanic with some common shop tools. You first bolt on the Gear Vendors replacement housing which has an eight-hole pattern to receive the overdrive. Then tighten the eight nuts and take the driveshaft with the new yoke (included) to the local driveshaft shop to be shortened (as per the instructions). One of the most important aspects to keep in mind is precise alignment of the driveline angles to ensure vibration-free operation. Plug in the electronics and fill the overdrive with the recommended lube, and you're ready to roll.

The electronic control box is installed inside the cockpit, under the carpeting at the toe-board. For a manual transmission, the switch for activating the unit mounts on the gearshift lever. For automatics, a foot-operated switch is used on the left side of the driver's footwell (like the old headlight dimmer switch).

The electronic module controls the splitter, so that it engages at the proper speed, and turns off automatically (at about 20 mph), in case you forget. The module also locks and unlocks the factory torque converter in an automatic. Overall, the gear splitter integrates seamlessly with the factory driveline, and is easy to operate when it comes time to drop the engine revs for long-range cruising-or make your move off the line.

Photos by Steve Temple and Larry Weiner


Gear Vendors - 800/999-9555 -

gear splitter, transmission upgrade
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