Gear Vendors Overdrive

Installing the Gear Vendors Overdrive
In the Silver Ghost 

A compilation of advice from Dave Browne, Bob Jefferson, Bill Kennedy, Steve Litman, David Morrison, Jim Stroman, Bob Thompson, Doug White and Rick Johnson of Gear Vendors, Inc.

Text and photos by Gil Fuqua

 Gear Vendors1 makes an electrically activated overdrive for the Silver Ghost (Photo 1) that provides a 22% reduction in engine RPMs when engaged at a given speed (Table 1).  The overdrive is based on a proven design created by Laycock Manufacturing and incorporates planetary gears that have been used for over a half a century in drive trains by GM, Ford, John Deere and Detroit Allison.  The Gear Vendors overdrive is rated to handle 30,000 pounds gross combined vehicle weight, more than enough reserve to handle the largest Ghost.

The advantages of the overdrive include lower engine and drive train noise, ability to achieve higher cruising speeds, and reduced RPMs at existing cruising speeds.  Reduced RPMs mean less wear on your engine and transmission, lower stresses on crankshafts and bearings from high rotational speeds (stress varies as the square of the speed)2 and may improve gas mileage.  Since the higher gearing allows you to drive faster, it’s important to remember you still have to stop your Ghost, and it takes longer to stop at higher speeds.  Think ahead and drive accordingly!

 The Gear Vendors overdrive provides about the same top gear performance for a standard 14/52 rear axle as an 18/52 ring and pinion.  The costs of the overdrive and new gears are similar; however, the overdrive is easier and faster to install and does not require the services of an expert gear fitter.  An advantage of the overdrive coupled with the 14/52 rear axle is the combination of low end pulling power of the original gears combined with the high speed cruising allowed by the overdrive.

The Gear Vendors overdrive comes pre-assembled with fittings that bolt directly to the Ghost’s torque tube (Photo 2). No structural modifications are required to the Ghost’s chassis or driveline and the overdrive installation can be easily reversed. The installation requires the torque tube to be unbolted from the sphere, and the axle backed out so that the front section of the torque tube can be removed and replaced with the overdrive unit (Photo 3). Once installed, a number of wires and switches are connected to the overdrive and control box to provide a means of control.

 

The Gear Vendors overdrive for the Silver Ghost is available from Sports Classics Ltd.3 (Bob Jefferson), Jim Stroman4 and Gear Vendors, Inc.   

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Section 1 - Disconnecting Torque Tube
Section 2 - Removing the Front Section of the Torque Tube
Section 3 - The Mathematics of an Overdrive
Section 4 - Checking Universal Joint and Bearnings
Section 5 - Installing Overdrive in Drive Line
Section 6 - Overdrive Lubrication
Section 7 - Connecting Speedometer and Electric Controls
Section 8 - Hooking up the Electronic Control Box
Section 9 - Hooking up Speedometer and Calibrating Output
Section 10 - The Overdrive in Operation
Section 11 - Overdrive Service
Section 12 - Crusing in Overdrive
Endnotes - Endnote
Table 1 - Silver Ghost Rear Axle Gear Ratios Comparisons
Table 2 - Engine Revolutions per Tire Turn
Table 3 - Overdrive Speedometer Gears for the Silver Ghost