Gear Splitter Install

Gear Splitter Install

Grabbing more gears for performance and efficiency

Having a few extra gears at your disposal can come in very handy. For instance, many drivers have likely experienced the following scenario on a steep hill: You're cruising along at a comfortable speed, right at the optimum spot for maximum engine torque. Then a slow-moving semi or RV pulls out in front of you, forcing you to lift off the throttle. Now that you've lost your momentum, you have two choices: To get back up to speed, you might try running a heavy throttle and high rpm, resulting in poor fuel efficiency. Or if you ease off the throttle and drop the revs, that may lug the engine, which can cause premature wear.

Close the Gap

Avoiding these problems might be as simple as having additional gears at your disposal. Whether you're running a manual or automatic, the spacing between those factory ratios is often too large a gap when you're towing a big load. The ratio you really need may fall somewhere in between them.

That's where a gear splitter comes in handy. The name comes from its ability to provide an increased number of underdrive gear ratios (those that lower the overall gear ratios) and overdrive gear ratios (those that make the ratios higher). As just one example, the Gear Vendors Under/Overdrive unit shown here adds five more gear selections to this diesel-powered Dodge Ram's 6-speed transmission allowing the driver to divvy up the powerband more precisely.

This type of product is not limited to diesel tow vehicles, however. It's found in a wide range of applications, including passenger cars, hot rods, delivery trucks, RVs, and even high-performance cars such as the Callaway Corvette. The unit has been in numerous record-setting competition vehicles as well, from land speed to drag racers. This transmission technology is a proven and reliable approach to improving performance.

Split the Difference

The unit consists 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 rocker switch on the 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. Splitting between the factory gear selections (hence the term "gear splitter") gives you better hill-climbing performance, among other benefits. Other pluses include lower transmission temperatures, improved fuel economy, and reduced noise in the cabin.

Installation of a gear splitter at Gear Vendors typically takes about a half-day or so, and is fairly simple in most applications. You first remove the transmission extension housing and 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). Plug in the electronics and fill the overdrive with the recommended lube, and you are ready to roll.

Bolt-On Application

On the 2003 3500 Dodge Ram Quad Cab shown here, a show truck nicely customized by Performance West Group, the transmission is a NV5600 manual with the NP 273 transfer case and 4.10 gears. For the show circuit, the truck is a shod with mind-boggling 37-inch tires. On the road, however, it runs on 285/80R17 tires.

Even more impressive is the Cummins HPCR engine pumping out 370 horses and a prodigious 750 lb.-ft. of torque. As big as those numbers are, Gear Vendors has handled much larger levels of power without a hiccup.

As shown in the accompanying photos, the install is a straightforward, bolt-on deal. The Gear Vendors unit is 14 inches long, requiring the two-piece driveshaft to be replaced with a single, shorter one. For this application, the tail shaft on the transfer case is removed and replaced with the Gear Vendors adaptor. One of the most important aspects to keep in mind is precise alignment of the driveline angles to ensure vibration-free operation.

As mentioned above, the electronic control box is installed inside the cab, under the dash. For a manual transmission, the switch for activating the unit while driving 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, and also locks out the overdrive when in four-wheel-drive. Overall, the gear splitter integrates seamlessly with the factory driveline, and is easy to operate when it comes time to make your move around that semi that gets in your way.


Gear Vendors, Inc., 1717 North Magnolia Ave., El Cajon, CA 92020, 800-999-9555, 619-562-0060,

gear vendors gear splitter
Previous Image Resume Next Image
Afraid of paying too much?
Get price quotes from dealers
near you... get ready to SAVE!

Get Internet Price