In fact, after The Brake Man big-brake installation, the GV unit was the first modification we made to the vehicle. We knew that what we had in store for this adaptable truck would be even more useable and efficient with the Under/Overdrive unit installed. This now makes the fourth vehicle that we have installed the unit in over the years, all different vehicles, and each one responsive to the GV addition. But none more perfect for this unit that the 7.3-liter Power Stroke diesel. No matter what vehicle-pickup, dualie or Excursion-it is equipped.
    Often mistaken for simply an overdrive unit, the Gear Vendors Under/Overdrive unit is much more than that. It should be thought of more as a transmission enhancer. And, when you consider the relatively small power band (limited rpm range) that diesels operate within, the GV unit is like adding a whole other set of gear rations, which, of course, is exactly what it does.
    In effect, the Gear Vendors Under/Overdrive unit doubles the number of gears that are available in the stock transmission. The Gear Vendors unit acts to split the distance between two gears. Think of it as if your vehicle had first gear, and then a first and a half; second gear, and then a second and a half, and so on. That means, if you have a transmission that features four forward gears, by timely engagement of the Gear Vendors unit, you effectively now have eight tighter ones. With some transmissions, the jump from first to second gear can be a long one, so the vehicle will have some trouble staying well within the power range, especially at

slow speeds, such as in rush-hour traffic. A GV unit can take care of the hunting that a normal auto transmission tends to do in such situations.
    Of course, that also means that if you have a transmission that is equipped with a factory overdrive, with the addition of the Gear Vendors unit, you will actually have an over-overdrive. That means there will be a gear over the overdrive. On the economic side, this can help keep fuel consumption to an absolute minimum, as a 300-500rpm decrease at speed can have a profound effect on mileage. So, without extolling the performance benefits of this package, fuel savings alone, over time, will offset the additional cost of this installation.
    Internally, the GV unit utilizes a planetary gear system as well as a Vertex clutch, which is cone shaped, to transfer the energy through the unit. To eliminate any problems of slippage, the GV unit has 700 psi of locking power to keep the Raybestos-equipped cone in contact. The Gear Vendors unit does not share fluid with the transmission, so there can be no problems due to cross contamination, or worry about proper fluid transfer.
    The system can be switched on an off manually with either a foot switch or one of the handle for those vehicles equipped with floor shifters. It also can be run in an "auto" position so that the computer will engage or disengage the unit at the pre-programmed mile per hour. The GV control module can even be programmed to control the tranny and torque converter as well as the Gear Vendors unit, thus allowing total control over the system.
    The Gear Vendors unit comes with an

impressive warranty. For those running an automatic transmission (and not using the vehicle in a business application), the Gear Vendors Under/Overdrive unit comes with a two-year unlimited-mileage warranty. Gear Vendors also offers this deal to prospective buyers: Put one of its units on your vehicle, and if you are not satisfied, call the company back within 30 days. Gear Vendors will take the unit off, and you get your money back. Guaranteed. That's right. If you buy one and don't like it, Gear Vendors will give you your money back. Now that is having a great deal of confidence in your product, but it isn't much of a gamble for Gear Vendors, because the unit works every bit as well as claimed. Also, with the correct input and output pieces, the GV unit will fit on virtually any vehicle.
    The Gear Vendors Under/Overdrive system has twice received the Best Engineered Product award at the annual SEMA show, first in 1981 and again in 1989. And in this day of brute power, big tires and multiple-use vehicles, including super rods, this device is about unique as anything on the market today. So follow along as installer Lin Roberts made short work of installing a Gear Vendors Under/Overdrive unit on our Low Buck Excursion. Of course, he has a lot of experience, but he had the complete installation done in about four hours. SR

Product Profile
Gear Vendors Dept. SPR, 1717N.
Magnolia Ave., El Cajon, CA 92020,
800/999-9555,
www.gearvendors.com

01 The Buckaroo Excursion is lifted into position on the Gear Vendors lift in preparation for the transformation to come.

02 The stock Ford 4R100 transmission is good but is about to become a tranny for all occasions. The first step, of course, is to remove the driveshaft and send it out to get shortened. On the big Ford, slightly less than 13 inches (12-8/10 inches) will be chopped out of the shaft.

03 A jack is placed beneath the transmission to hold it up in place while the rear trans mount is removed.

04 The output shaft speed sensor is located on top of the stock tailhousing. The plus is pulled.

05 A drip pan is placed beneath the rear housing, and with the housing bolts removed, the snout is carefully pulled off.

06 There is a spring and clip that connects to the parking-brake system that tends to fall out. Don't lose them, because these need to be reinstalled.

07 The output shaft speed sensor has been removed from the stock tailhousing and is installed into the Gear Vendors extension housing.

08 Gear Vendors recommends that the gasket hat fits between the transmission and the GV extension housing be put in place without any sealant.

09 With the seal and bushing located within the GV unit lubricated with white lithium grease, the extension housing is slipped into place. The nuts that hold the adapter to the case are installed and need to be torqued to about 18 lb-ft.

10 The rear tranny mount is installed and the jack removed from beneath the tranny case.

11 The output shaft sensor is plugged back in.

12 With the extension housing in place, the job is nearly a third of the way done.

13 With the GV extension housing in place, measurements are again taken for the driveshaft.

14 A coupler is used to connect the output shaft on the tranny to the Gear Vendors unit. To get the correct amount of slip, first the output shaft is gently tapped with a rubber mallet to ensure that the shaft is firmly seated. The coupler is greased with white lithium grease and slid over the output shaft.

15 With the gasket in place, a straightedge is placed over the end of the assembly, and shims (they are 0.0020-inch thick) are slid between the edge of the coupler and straightedge until the correct amount of spacing (0.0000.015 inch) is achieved.

16 The shims actually fit inside the coupler and against the output shaft of the tranny. So, the coupler is pullet out, the shims are inserted and the coupler is slid back in place.

17 With the coupler in place and the splines lubricated, the unit is installed. It is recommended that you tighten the mounting bolts in a crisscross pattern and torque them to 6-9 lb-ft. Applying blue Loctite to the threads also is recommended.

18 Because the speed is electronically calibrated through the stock tranny, a freeze plug is placed in the hole on the Gear Vendors unit.

19 On the electronics part of the install. The first step is to remove the leads to the battery.

20 The plug is pulled to gain access to the main harness.

21a This wire is the one that provides the vehicle speed to the computer.

21b A clip is placed on the wire, and that wire goes to the Gear Vendors control module. The black wire is a ground wire.

22 A good place is found on the dash switch, or selector switch, as it also know. It is held in placed with a metal mount that is screwed into the lower dash.

23 It is mounted to the bottom of the dash. The individual switches and lights can be removed from this mount and flush-mounted into the dash. Gear Vendors also supplies small LED-type lights for those who don't have the room for the larger lights.

24 Because this vehicle uses a column-mounted gear-select system, a foot switch will be used to actuate the GV unit when it is in the manual mode. If the vehicle uses a floor-type shifter, GV also has shift-knob-type switches available.

25 The GV system is well designed, with easy-to-connect plugs in place as it comes from the factory. All the connections are color coded, and some even use telephone-type connections This, thankfully, makes the job of connecting the various wires simple.

26 The Gear Vendors control module is the brains of the operation.

27 It is recommended that the GV control module be installed inside the cab and away from the elements, such as heat and water, which could cause harm to the unit. This was accomplished by affixing it to the firewall beneath the dash.

28 Power to the Gar Vendors computer comes from the main fuse box. The lead will be run from a "key-on" source, because it is not desirable to have constant power running to the GV computer.

29 A good ground is imperative for proper operation of the GV unit, or qny electronic device, for that matter.

30a Rather than drill more holes in the floor,

30b Roberts uses the existing throughway to run the wires that run from the control module to the solenoid.

31a One look at this clean installation shows the professionalism of the guys at Gear Vendors.

31b Wires are run smoothly, and all excess wire are carefully wound up and zip-tied out of the way.

32 Another input that must be run to the GV control module is the converter lockup. It is located in the main harness that runs to the tranny and separated out.

33a-b Again, GV makes the job easy, as the connections are well marked and the splice is a no-brainer.

34 Considering the problems that exposure to the elements could cause, this splice is taped up well.

35a-c Lithium grease is applied to the splines on the output shaft on the GV unit before installing the driveshaft.

36a-c An electronic level is used on the Gear Vendors housing, the driveshaft and the rear U-joints to ensure all are within tolerances.

37 With that, the Gear Vendors Under/Overdrive unit is in place and ready to run. It is recommended that the vehicle be driven a mile or two before engaging the GV unit to ensure proper fluid distribution in the hydraulic system.