Gear Vendors Overdrive Dodge 4 sp automatics 518, 618 or 47RH


Dodge Automatic Transmissions - Gear Vendors Save Gas or Diesel Fuel Extend Mileage, Extend Engine Life, Start Saving Money Today!

Does your Dodge Ram pickup need more power to climb hills or tow with heavy loads? What if at the push at the touch of a button, you could have taller gearing for cruising down the Dodge Overdrive, Dodge 4 Speed Automaticshighway with the lower engine RPM's and improved fuel mileage? See our Dodge Automatic transmission application guide. Our Gear Vendor overdrives are available for Dodge automatic transmissions using: 4 speed automatic transmission models A-518, A618 & 47RH. Our Dodge Ram pickup overdrive transmission provides 500 to 600 less RPM's plus 20% increase in fuel economy. You'll need an auxiliary overdrive transmission capable of gear splitting behind your transmission. The toughest built best performing auxiliary overdrive transmission you can buy is the Gear Vendors overdrive from Order yours online or call us at 800-216-1632!


See How It Works, Guaranteed Amazing Performance for Your Dodge


Gears are multipliers of torque and our Ratio Splitting capability allows you to shift to a gear with more mechanical advantage than the next stock gear in automatic transmissions and wide ratio manuals. This also means engine rpm drops about half what it did without the Gear Vendors and so rpm is sustained - higher torque and rpm on shift = more Horsepower. When shifted into overdrive final gear, reducing both rpm and torque to reduce the manufacture of HP when steady cruising to improve fuel mileage and decreases wear on your engine. Two-year warranty rated at 30,000 pounds applications for Dodge Ram pickup, most beneficial when used in commuters, tow vehicles, 5th wheels and Motor homes.
Our Dodge overdrive kits are very complete and are designed for your specific vehicle. Detailed installation instructions are included in the kit, and installation is also available. Related to fuel economy, performance, and emissions — Gear Vendors overdrive units include state of the art electronics circuits that keep your vehicle in the optimum performing gear. Whether you are driving an older non-computer controlled vehicle or a late model with all the latest emissions computers, our electronics provide the interface to ensure maximum performance and correct rpm without lugging or over revving in the wrong gear. The OE factory programming remains intact and our processor just makes it aware of the actual ratio 1,000 of times per second. In older vacuum or throttle linkage transmissions the stock governor on the output shaft instantly slows down the moment the overdrive shifts and so automatically moves the shift point in any overdrive gear up by the correct 28.6%. So both electronic and non-electronic automatic transmissions gain a group of features including a passing gear or climbing gear that is automatically available without driver intervention and is at the split between 2nd and 3rd where you really want it. Need more information on how to save gas or diesel fuel?

Gear Vendors's Complete Kits Ensure a Smooth Installation for You


Gear Vendors overdrive kits are complete with adapters. Our Gear Vendors overdrives are supplied with specific adaptation kits for each model of transmission model. By supplying specific extension housings to each model/brand transfer case Gear Vendors is able to have a better product withgvyoutubesema2008.jpg increased engineering benefit to the final installation. Fact is, when you are in 4X4 there is very little desire to use GearSplitting and overdrive unless you are racing (and we do make the in-between kit for that purpose), it's 2wd where the benefits of overdrive and additional gears are most needed. See YOUTUBE video for more information. All our kits bolt directly to the rear of the transmission, you can manually control the unit or we suggest you flip the switch when leaving the city limits sign and turn it off when you get to the next city limit sign. No additional crossmembers are required and you retain the factory ground clearance instead of moving the transfer case rearward which puts it at or nearer the middle of the wheelbase where ground clearance is most critical. You get all the benefits of the Gear Splitting performance and overdrive economy (see your appropriate transmission under Dodge) and the best auxiliary transmission you can buy.

Free Technical Support, Get Expert advice about your vehicle's performance with our Gear Vendors Overdrive. Call toll free at 800-216-1632. More fuel milage 20%, 600 RPM reduction in Engine RPM means longer life and you save Money!

You get all the benefits of the GearSplitting performance and overdrive economy (see your appropriate transmission under Dodge) and the best auxiliary transmission you can buy. Give our overdrive expert a call toll free 800-216-1632. He can answer your questions and help you pick the correct model for you application. Get free telephone support during installation when you purchase from

  • You need quality.
  • You'll want reliability.
  • You want performance 22% Overdrive.
  • You want better mileage 20% more fuel economy!

YOU WANT A Gear Vendors


Bolt on Performance & Economy! 



  • Save Fuel
  • Extend Engine Life
  • Save Money
  • 30,000 lbs Capability

Select your vehicle from the following table to see detailed information on improving your vehicles performance and saving money today!

Dodge 4 Speed Automatic Truck/Motor home   Dodge A-518/A618 4 Speed Automatic Final Drive Ratio
Dodge 4 Speed Automatic Performance Car/Street Rod   Dodge 4 Speed Automatic Application Chart & Pricing
    DODGE RAM Horsepower and Torque Curves


DODGE 4-Speed Automatics Trucks/Motor homes

There are two common Dodge 4-speed automatics: The non-lockup 518 and the lockup version designated 618/47RH. The 518 was used prior to computer controls until 1994. Everything 1994 and newer has the lockup torque converter (618/47RH). The gear ratio of each of these transmissions is the same. (see Final Drive Ratios)


The 4-speed automatic is basically the old venerable 727 with an overdrive bolted on as a tail case. The first thing you may have noticed is that the drive ratio of the factory transmission is very tall (.69). The Gear Vendors .78 to 1 ratio will not hunt (shifting back and forth under load) and will also reduce temperatures in the main transmission by as much as 100 degrees on warm days. Consequently all our customers tow in the GV ratio and greatly extend the life of the transmission. Trucks running empty can make use of double overdrive for great economy and extended engine life.


Gear Splitting is the feature that allows the UNDER/OVERDRIVE to shift between the gears. You will now have approximately 1/2 the drop of engineer pm from one gear to the next when you want power. This is why a Gear Vendors will give you more power than any underdrive or overdrive on the market (see common questions). By keeping torque multiplication higher and engine rpm narrower you increase engine performance by typically more than 40hp and 60lb ft. of torque without any modifications to the engine (see Final Drive Ratio charts and Horsepower and Torque curves in this section)(see also common questions on performance modifications).


This is why big trucks use gears (most 18 wheelers have 15 to 21 gears) instead of modifications. Because gearing gives them performance which actually improves the reliability of the engine. The heavier you are loaded the more you need a Dodge Overdrive.


If you already have engine modifications (chips, exhaust, fuel increases, etc.) the Gear Vendors will let you get the most from them through working in narrower rpm ranges when loaded and also by adding torque multiplication to make it easier on the engine and trans.


The Gear Vendors comes with a 2-year unlimited mileage warranty (on non commercial applications ) and a 30 day money back guarantee that you will love the performance (see warranty for details). The Gear Vendors is the only after market performance device or auxiliary transmission that comes as original factory equipment on new cars, trucks, vans or Motor homes Over 1 million in the 80’s and 90’s were installed by manufacturers on vehicles; i.e.; Ford Diesel Transit Vans (European market), Volvo gas and diesel, Fleetwood, Allegro, Rexhall, Monoco and others Motor homes and GM’s Twin Turbo Callaway Corvette.


If you’re vehicle is heavily loaded or you just love performance the Gear Vendors is the ultimate option. Call our Overdrive Expert at (800) 216-1632.

DODGE 4-Speed Automatic Performance Car/Street Rod/Sport Truck

The 518/618/47RH factory overdrive transmission was designed for improving Dodge’s CAFÉ (Corporate Average Fuel Economy) ratings. Because of this it has a very tall .69 overdrive ratio. The Gear Vendors fixes the wide ratio problems so that when you want performance you have a gear between each of the factory ratios. This gives you approximately half the drop in the engine rpm and torque multiplication (see final drive ratios).

You can easily have increases in horsepower in the 50+ range and torque boosts of 70lb ft. just by gear splitting. With 8 forward gears available the motor stays in a narrow rpm band of performance. The .78 ratio of this overdrive gives an alternative overdrive ratio to the very tall factory gear and the Gear Vendors can e used with virtually unlimited horsepower (if 1200hp or less it gets the standard product). If you have a car or hotrod truck, also read the 3-speed 2wd section. If you have a truck used for towing, read also the GM4-speed automatic truck section.


Final Drive Ratio 518/618/47RH 4-Speed Automatic

Axle Ratio

  Rer End Ratio 4.56 4.1 3.9 3.54
  Transmission Ratio

Final Drive Ratio

1st 2.45 11.17 10.5 9.56 8.67
Over 1.91 8.71 7.84 7.46 6.76
2nd 1.45 6.61 5.95 5.66 5.13
Over 1.13 5.15 4.64 4.41 4
3rd 1 4.56 4.1 3.9 3.54
Over 0.78 3.56 3.2 3.04 2.76
4th Dodge O/D 0.69 3.15 2.83 2.69 2.44
Double Over 0.54 2.46 2.2 2.1 1.9

 Dodge 4 Speed Automatic Trans Products 



Dodge Application Guide 2 Wheel Drive 4-Speed Automatic

Part Number





3D0171A A-518 4 Speed Automatic 2wd w/overdrive Spicer 1350 series front & rear yokes, see kit. Replaces existing carrier bearing in 2 piece drive shaft or becomes carrier bearing in on piece. All application 1989-1993 including Cummins 6BT.


3D0518A Automatic 4-Speed 518 Direct Mount. Replaces factory 2-Wheel Drive tailhousing with factory Dodge 4x4 tailhousing, see kit.    $3545.00
3D0174A A-618 4 Speed Auto 2wd with overdrive Spicer 1350 series front and rear yokes, see kit. Replaces carrier bearing in 2 piece drive shafts or becomes carrier bearing in one piece shafts. All applications 1994 and newer Cummins 6BT diesel and Dodge V-10 gas.


3D0174E  A-618 4-Speed Automatic 2-Wheel Drive with Overdrive. Replaces carrier bearing in 2pc. Driveshaft applications, or becomes carrier bearing in one piece applications.  Spicer 1350 front and rear yokes, installation is $200 additional, see kit. All applications 94 and newer Cummins 6BT diesel and Dodge V10 gas.   $3145.00
3D0618A Automatic 4-Speed 47 RH (618) Direct Mount  Replaces factory 2-Wheel Drive tailhousing with factory Dodge 4x4 tailhousing, see kit.  94-95 with Governor.   $3545.00
3D0618E Automatic 4-Speed 47 RH (618) Direct Mount Replaces factory 2-Wheel Drive tailhousing with factory Dodge 4x4 tailhousing, see kit. 96-97 without Governor.     $3545.00
3D0618G Automatic 4-Speed 47RE (618) Replaces factory 2-Wheel Drive tailhousing with factory Dodge 4x4 tailhousing, see kit. 98 and Newer Diesel application.    $3545.00

We have included a frequently ask questions section that may answer some of your questions, don't see answers you need, just give us a call we will be happy to review your application with you. The following links provide specific application information, performance data that you can expect and the price data for your specific vehicle.