GM Facts

Under/Overdriveâ„¢ Facts

Straight facts about GEAR VENDORS more power enhancing gas saving transmissions!

You want more power to climb hills or tow with heavy loads, plus at the touch of a button taller gearing for cruising down the highway with the lower engine RPMs and improved mileage. You’ll need an auxiliary transmission capable of gear splitting and overdrive. The toughest built best performing auxiliary transmission you can buy is the UNDER/OVERDRIVEâ„¢ from GEAR VENDORS INC.


Each UNDER/OVERDRIVEâ„¢ auxiliary transmission represents the combined effort and technology of GEAR VENDORS, INC. (the largest producer of overdrives in the world). The very finest in manufacturing, assembly, and R&D facilities are available. Our customers ride with confidence knowing that GEAR VENDORS, INC. offers the only auxiliary transmission available that is approved and used by new car and motorhome manufacturers. Component quality is unsurpassed, Sheffield steel planetary gear set, 4500 ft. lb. roller clutch, forged ring gear assembly, common vertex (cone) full throttle shift clutch.


ford aux transmissions

No matter how much enjoyment you derive from the improved performance of gear splitting on hills and overdrive when cruising, if your auxiliary transmission leaves you stranded in the middle of the highway, you’ll wish you never made the purchase. GEAR VENDORS current “P”-Type UNDER/OVERDRIVEâ„¢ is the toughest rated product in the industry. Guaranteed to 30,000 lbs. GCVW, the unit relies on a mechanical lockup roller clutch (Sprague) just like automatic transmissions do to handle the extreme torque peaks of initial take off and change of direction from reverse to drive. It is a completly self contained system with its own integral pump and pressurized lubrication, (features not found in any other auxiliary transmissions). Ask these questions of any other auxiliary transmission manufacturer:

  1. Can the unit get stuck in neutral?
  2. What if the unit loses all its fluid (leak)?
  3. Can I shift the unit under any throttle condition (including full throttle)?
  4. If a major problem occurs, can I simply shut it off and continue driving?

GEAR VENDORS knows the RVer wants a gear splitting/overdrive product that works as well as the rest of his vehicle and can never leave him stranded, period! Price is secondary, Reliability First.


Power is certainly the No. 1 reason more people choose the GEAR VENDORS UNDER/OVERDRIVEâ„¢.There is no other auxiliary transmission available which can split gears as effectively.


In vehicles with automatic transmissions the unit is intended to shift at any throttle position including full throttle and delivers a crisp responsive shift. Shift it as much as you like . . . the internally activated common vertex clutch is designed to last 250,000 miles. Vehicles with manual transmissions also benefit from the constant mesh planetary gear design as both in-shifts and out-shifts are as simple as depressing the vehicles clutch pedal and pushing a button. No syncros to wear out, no grinding gears or misshifts possible. The systems sophisticated planetary design has very low friction which means not only will a GEAR VENDORS last longer, but it’s quieter and has less power loss (less than 1hp per 400hp) than any other auxiliary transmission. All GEAR VENDORS UNDER/OVERDRIVESâ„¢ offer a .78 to 1 (22%) overdrive ratio, designed to be the ultimate gear splitting and overdrive ratio for today’s RV’s. Anything less than 22% would be less effective at slowing RPMs while cruising in overdrive . . . anything more than 22% wouldn’t be effective as a gear splitter when you need power to climb hills or to pass slower traffic. Performance through proper gearing is the cornerstone of GEAR VENDORS UNDER/OVERDRIVEâ„¢.


There are many devices advertised as remedies for poor gas mileage. Fact is, anyone who tells you how much you are going to gain is just trying to sell you something. Every vehicle represents many different situations, different drivers, different conditions of tuning, different climates and altitudes. The GEAR VENDORS UNDER/OVERDRIVEâ„¢ is not some magic pill, but twice the number of forward gears for combating all these different conditions.


We at GEAR VENDORS believe that proper available gearing is the best solution to problems of power and economy. Why modify your engine for more horsepower and possibly deter from its reliability or void the manufacturer’s warranty when every time you shift there are such big changes in transmission ratios that your engine RPMs fall completely out of the power range. You need that half gear between each of your current gears which will not only keep the engine making power but improve its useful life and reliability. You’ll no longer be overreving the engine in too low a gear or lugging it in too tall a gear. Plus out of the same device get a gear that lets the engine slow down without slowing down the vehicle which not only can save you a lot of fuel, but greatly reduce engine wear. Imagine the same engine work (RPMs) that currently take you 15.56 miles – can take you 20 miles in overdrive (that’s a lot less wear) not to mention the fuel savings and longer range. There is a lot less engine noise in overdrive also. These are some of the reasons Volvo, whose cars have the longest average life expectancy of any automobile company in the world (21 years) bought more than 1 million of these units over the years.

Get geared for power and economy with a GEAR VENDORS UNDER/OVERDRIVEâ„¢