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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.
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Unbolt the tail-shaft housing on the stock transfer case. Be sure to clean off the old gasket material thoroughly.
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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.
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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.
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This is how the housing and the adaptor bolt onto the factory transfer case.
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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.
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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.
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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).
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Here's how the master switch for electronic module fits in the dash.
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With the master control module turned on, we hit the red actuator button on the gearshift lever.
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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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