Performance
gear splitter install

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.

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Photo Guide
gear vendors gear splitter
Since the Gear Vendors unit connects directly with the driveline, the two-piece driveshaft needs to be replaced with a shorter, single-piece shaft. The rear driveshaft comes out first, then the front driveshaft and the center support housing.
tail shaft housing
Unbolt the tail-shaft housing on the stock transfer case. Be sure to clean off the old gasket material thoroughly.
gear splitter adapter
At left is the Gear Vendors tail-shaft housing; on the right is the adaptor for the gear splitter. Add RTV silicone sealant to the tail-shaft housing before installing it.
gear splitter how to
Carefully install the new housing. Careful alignment of all the parts is critical. Some shimming of the coupler between the transfer case shaft and the Gear Vendors unit may be necessary.
gear splitter bolt on
This is how the housing and the adaptor bolt onto the factory transfer case.
gear splitter underdrive overdrive
The Gear Vendors Under/Overdrive is fairly compact, and will fit underneath just about any truck. Here's how the unit looks after bolting it to the adaptor. A new, shorter driveshaft needs to be custom fitted.
gear splitter electronic control module
The electronic control module fits under the dash, and the actuator switch goes on the shift lever. Another electronic component fits underneath the pedals in the footwell.
gear splitter speed sensor
A speed sensor is part of the system, so that it engages at the proper speed (about 47 mph), and turns off automatically (at about 20 mph).
gear splitter dashboard switch
Here's how the master switch for electronic module fits in the dash.
gear splitter actuator button
With the master control module turned on, we hit the red actuator button on the gearshift lever.
gear splitter install lower RPM results
Without the gear splitter engaged, we cruised at 70 mph at slightly more than 2,200 rpm, but with the gear splitter engaged, the tach drops to 1,700 rpm, even though we're still running at 70 mph. That's a difference of 500 rpm, a 22 percent reduction in the drive ratio.



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