Dodge 4/5/6-Spd Auto

DODGE 4-Speed Automatics Trucks/Motorhomes

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 ’94 and newer has the lockup torque converter (618/47RH). The gear ratios of each of these transmissions is the same. (See Final Drive Ratios)

Performance West Group's, 3500 Truck

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 overdrive 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 trans. Trucks running empty can make use of double overdrive for great economy and extended engine life.

GearSplitting is the feature that allows the UNDER/OVERDRIVE to shift between the gears. You will now have approximately 1/2 the drop of engine rpm 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 modification to the engine (see Final Drive Ratios charts and Hosepower and Torque curves) (see also Common Questions on performance modifications).

trucks, motorhomes

This is why big trucks (Kenworths, etc) use gears (most 18 wheelers have 10 to 15 gears) instead of other modifications. Because gearing gives them performance which actually improves the reliability of the engine. The heavier you are loaded the more you need a GEAR VENDORS.

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 transmission.

The GEAR VENDORS comes with a 2 year unlimited mileage warranty (on noncommercial applications) and a 30 day money back guarantee that you’ll love the performance (see Warranty for details). The GEAR VENDORS is the only aftermarket performance device or auxiliary transmission to come as original factory equipment on new cars, trucks, vans, or motorhomes. Over 1 million in the 80’s and 90’s were installed by manufacturers on vehicles; ie: Ford Diesel Transit Vans (european market), Volvo gas and diesel, Fleetwood, Allegro, Rexhall, Monaco and other motorhomes, and GM’s Twin Turbo Callaway Corvette.

If your vehicle is heavily loaded or you just love performance the GEAR VENDORS is the ultimate option. Call our customer service line (800) 999-9555 and we will arrange for purchase and installation at your authorized dealer or your preferred mechanic.


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

Direct Mount Option

The 518/618/47RH factory overdrive transmission was designed for improving Dodge’s CAFE (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 that give you approximately half the drop in 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 the GEAR VENDORS gives an alternative overdrive ratio to the very tall factory gear and the GEAR VENDORS can be used with virtually unlimited horsepower (if it is 1200hp or less it gets the standard product). If you have a car or hotrod truck also read the 3-speed 2 wheel drive section. If you have a truck used for towing read also the 4-speed automatic truck section.



Gears Under/Overdrive

Find your transmission and rear gear multiplier below. The Final Drive Ratio shows you how many times the engine turns for one complete turn of the tires. This Final Drive number is also your torque multiplier when in that gear. GEAR VENDORS reputation for being the best is because of its sophisticated planetary construction. This means GEAR VENDORS is the only auxiliary intended as a GearSplitter behind automatics and the nicest to work behind both automatics and manuals. You are able to shift half gears that keep the engine in the power. Any auxiliary that requires you to let off the accelerator or is not intended to shift frequently is not going to give you this performance.

There is not room here to cover all the details so call the factory to discuss the full benefits demonstrated on these charts.

Axle Ratio
4.56 4.10 3.90 3.73 3.54
Trans Ratio Final Drive Ratio
1st 2.45 11.17 10.05 9.56 9.14 8.67
Over 1.91 8.71 7.84 7.46 7.13 6.76
2nd 1.45 6.61 5.95 5.66 5.41 5.13
Over 1.13 5.15 4.64 4.41 4.22 4.00
3rd 1.00 4.56 4.10 3.90 3.73 3.54
Over 0.78 3.56 3.20 3.04 2.91 2.76
4th Dodge O/D 0.69 3.15 2.83 2.69 2.57 2.44
Double Over* 0.54 2.46 2.20 2.10 2.01 1.90
*Note: Double Overdrive not to be used when towing or loaded.

Call or e-mail the factory to find out all the options availalbe in your performance application.

DODGE/DODGE RAM 4-Wheel Drive Truck/Van 4/5 Speed Automatics

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