Gear Vendors Overdrive Unit, Ford 3 Speed Auto Transmission C4 & C6

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

Does your Ford need 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 RPM's and improved fuel mileage, see application guide. Our Gear Vendors overdrive for Ford are available for the following automatic transmissions: C4 and C6 3 Speeds. Our Ford 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

See How It Works, Guaranteed Amazing Performance for Your Ford

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 Ford, most beneficial when used in commuters, tow vehicles, 5th wheels and Motor homes. Our overdrive kits are very complete and are designed for your specific vehicle, detailed installation instructions are included in 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 a 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 supplies with specific adaptation kits for each model of transmission model, the kits are completed. By supplying specific extension housings to each model/brand transfer case Gear Vendors is able to have a better product with gvyoutubesema2008.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 switch when leaving city limits sign and turn it off when you get to 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. Read customer testimonial

Free Technical Support, Get Expert advice about your vehicle's performance with our Gear Vendorss 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 GM/Dodge/Ford 2wd) and the best auxiliary transmission you can buy. Give our overdrive expert a call toll free 800-2161632 he can answer your questions and help you pick correct model for you application, and 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 and Economy! 



  • Save Fuel
  • Extend Engine Life
  • Save Money
  • 30,000 lbs Capability
  • Slowing the engine down so that the same rpms that currently take you only 500 miles will now take you 640 miles.


You want more power to climb hills or tow with heavy loads

At the touch of a button taller gearing for cruising down the highway with the lower engine RPM's and improved fuel mileage. You'll need an auxiliary overdrive transmission capable of gear splitting. The toughest built best performing auxiliary transmission you can buy is the overdrive from Drivetrain Specialist. 22% overdrive 20% fuel savings, two year warranty rated at 36,000 pounds applications for Ford pickup trucks with 3 speed automatic transmissions, most beneficial when used in tow vehicles, 5th wheels and Motorhomes.  Ideal for both diesel and gas pickup trucks and other vehicles with early C4 or C6 transmissions. Also available for early Ford automobiles. Our overdrive kits are very complete and are designed for your specific vehicle, detailed installation instructions are included in kit, installation is also available. Select your vehicle from the following table to see detailed information on improving your vehicles performance and saving money today!

Ford 3 Speed Automatic Truck/Motorhome   Ford C4/C6 3 Speed Automatic Final Drive Ratio
Ford 3 Speed Automatic Performance Car/Street Rod   Ford C4/C6 3 Speed Automatic Application Chart & Pricing


FORD 3-SpeedAutomatic Truck/Motorhome

With the Gear Vendors dash switch in “auto” you will have automatic overdrive just like the vehicle came with a factory system. The dash switch can either be mounted in our under dash bezel or the custom in dash bezel like the Fleetwood Limited's that came factory with the Gear Vendors. The Gear Vendors will shift in and off without attention of the driver and can be used while towing up to combined weight of 30,000 lbs. An interactive floor switch is positioned for the left foot (just like a headlight dimmer) to give manual control at any given moment so that you can turn the overdrive on/off for performance and gear splitting.

Performance while accelerating or climbing grades is greatly improved by the availability of 6 forward ratios (see final drive ). With approximately 1/2 the drop in engine rpm on each gear change and the ability to downshift at 1/2 the intervals (much smother an with the stock only transmission) performance gains of over 40+ horsepower and 60lb ft. of torque are typically minimum. (See Horsepower and Torque curves).


Most importantly you are getting this horsepower and torque without modification in any way to the engine. Any other way of increasing power (chips, induction, exhaust, fuel) all put stress’s beyond the original equipment. With the Gear Vendors OVERDRIVE you get this power because gears are multipliers of torque, plus the engine can be kept in a narrower (better performing) rpm range when power is needed. For this reason, if you do have performance modifications the Gear Vendors also helps them work to their maximum potential. Not only do you get performance without engine modification, but the overdrive will pay for itself in fuel mileage alone. Add to this the savings in wear you get from slowing the engine down 22% so that the same rpm's that currently take you only 500 miles will now take you 640 miles.


Most vehicles will experience mileage increase in the 20 percent region if driven at the same top speeds as they are without the Gear Vendors.  Increased mileage and reduced engine wear is why all vehicles today come with factory overdrive


The Gear Vendors OVERDRIVE will do more for this vehiclethen any Underdrive or Overdrive on the market. You will get all the features normallyassociated with an underdrive except a gear below first, plus all the economy ofoverdrive.  Because Gear Vendors is the only product you can shift under throttle you will have far greater performance and economy. The Gear Vendors comes with the best money back guarantee (see warranty for details). There is not room here to discuss every situation that arises where additional gears and torque multiplication help your vehicle perform. Look at the final drive ratio page and then call and get one,you will be absolutely glad you did.

FORD 3-Speed Automatic PerformanceCar/Street Rodford3speedautoperfcarsrtr_l.jpg

Starting at about 2200 dollars (depending on models) the Gear Vendors is not the cheapest way for you to get overdrive (a rebuilt wreaking yard AOD is probably cheaper) but the Gear Vendors is by far the best way. Horsepower handling is the first issue.  A Gear Vendors will handle 1200+ horsepower reliably.  This is why you have seen GearVendors in 8 second 1/4 mile cars in publications like Hot Rod and National Dragster.  This is also why all GM Callaway Corvettes with automatics came with a TH400 and Gear Vendors instead of the 700r4 which is the base Corvette transmission and comparable to the AOD Ford.  If you’re running more then 1200 horsepower (and we have customers that are) then talk to us at the factory as there are some hydraulic changes we do for vehicles up to 2000hp.


Horsepower aside, there are several other reasons you will prefer a Gear Vendors to any factory overdrive automatic. You will have a dash switch that allows both manual ad automatic operation. With the switch in “auto” the vehicle will act just like it came from the factory with overdrive. The overdrive will kick in at 47 mph or whatever the EPROM is set for in our electronics and turn back off at slower speeds without attention of the driver. The ratio is .78 to 1 (see the final drive ratio charts on page 17). This equates to 28% faster vehicle speed at the same rpm.  Or, take your existing rear gear multiplied by .78 (i.e. 4.10 X.78=3.20).  In this example a vehicle with a 4.10 behaves just like it had 3.20s when the overdrive is engaged. This is just the right amount of overdrive as any taller would require a lock up converter or create excessive converter slippage. With the .78 to 1 ratio you’re good with any torque converter you chose for high performance street/strip use.


Another great feature of the Gear Vendors is that you will have a full 6 forward ratios when you switch to manual on the dash switch Pull into low, accelerate, then hit our button (on the shifter or the floor), a green light appears indicating overdrive and your in first over which is right between 1st and 2nd . Then shift to 2nd and turn us off. Then rev back up and hit the button for 2nd-over. Then 3rd and 3rd-over. See more information on Gear Splitting in the Drag Racing section. The performance and sound of the motor is tremendous as it goes through 6 full throttle close ratio shifts. You are in each gar 1/2 the time you are now so the car is not only faster but it also feels and sounds much faster.


Check out the unlimited horsepower warranty and money back guarantee (under 3-spd truck) and the simple installation in the dimensions section.Then order by calling (800) 216-1632


Find you transmission and rear gear multipliers above. The Final Drive Ratio shows you how many times the engine turns for one complete turn of tires. This Final Drive number is also your torque multiplier when in that gear.  Gear Vendors reputation for being to best is because of its sophisticated planetary construction. This means Gear Vendors is the only auxiliary intended as a gear splitter 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 band.  Any auxiliary that requires you to let off of the accelerator or is not intended to shift frequently is not going to give you this performance.



Final Drive Ratio C4 and C6 3-Speed Automatic  

Axle Ratio

  Rear End Ratio









  Transmission Ratio

Final Drive Ratio

1st 2.46 12.62 12 11.22 10.09 9.59 9.18 8.73 7.94
Over 1.92 9.84 9.36 8.75 7.87 7.49 7.16 6.81 6.19
2nd 1.46 7.49 7.12 6.66 5.99 5.69 5.45 5.18 4.72
Over 1.14 5.84 5.55 5.19 4.67 4.45 4.25 4.04 3.68
3rd 1 5.13 4.88 4.56 4.1 3.9 3.73 3.55 3.23
Over 0.78 4 3.81 3.56 3.2 3.04 2.91 2.77 2.52


Ford Application Guide 2 Wheel Drive 3-Speed Automatic

Part Number





3DFS40A C-4 3 Speed Automatic Replaces 13" tail housing Ford light duty vans pickups and cars


3DFS41A Shorty C-4 3 Speed Automatic Replaces 13" tail housing Coverts long shaft C4 to a short 4wd version (That's 5 .5" shorter) Muscle car applications w/limited tunnel & driveshaft length


3DFS60A C-6 3 Speed Automatic Replaces 14" tail housing, also see 3D0063 below Ford vans, pickups, class C Motorhome and cars, including motorhome's and passenger cars including 6.9 and 7.3 diesels


3DFS63A Shorty C-6 3 Speed Automatic Replaces 14" tail housing, uses GV supplied output shaft, shortens package by 10" Used for Cobra kit cars and other short wheel base cars. Shortens package by 10". Some early model Ford trucks, with fixed yoke.



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.

1984 Ford Ranger

On 9/14/09 I ordered the GV as a final touch for my project 1984 Ford Ranger. It was promptly shipped on 9/22/09. UPS delivered it to me in Massachusetts on 9/29/09. First I was impressed with the neat, very nice job, your packing and shipping crew did. As I laid out all the parts on a table in my garage, and read through the install manual, it became clear to me that this was a high quality product, from a top notch company. The next morning I drained my tranny, removed my driveshaft and tailshaft housing. Just 4 hours passed before I had the adapter, GV unit, electrical components, and wiring harnesses installed. (the wiring harness connections were so well marked and color coded that "even a caveman could do it!!" ) The piggyback adapter for plugging my aftermarket electric speedometer sensor to the GV sensor was a real nice surprise, it made it so easy, and I later found that re-programming the speedo was not even needed. So off to my local driveshaft guy, (Mitchell Differential+Driveshaft, in Shrewsbury, Ma.) The next morning after picking up my new shorter driveshaft, (decided to keep original in case of any future changes) I installed it to find 5/8" free play on slip yoke, Wow!! I must have measured right! Promptly I filled the GV with recommended synthetic gear oil... $$$!!! and filled my tranny fluid. Now, I did one last inspection of all my work, and prepared for the big road test!

Gear Vendor Overdrive Installation in 1984 Ranger Engine  Gear Vendor Installation 1984 Ranger gv_ranger_inst_3.jpg

As per the instructions, I drove a few miles with the overdrive off.  Now my finger was shaking with anticipation just as it was about to depress the GV button........(will all my time, and all that money be worth it?)......... click. YES!! It worked perfectly, just as described on your website. My 302 w/roush heads and all the other goodies seemed to come alive like never before, it seems to be in the peak powerband right up through all of my new-found 6 gears! The Performance Automatic Super Streeter C4 seems to be made for the GV. What a huge difference on the interstates at 70 mph the rpm is now down from just over 3000 to 2400, and it is quiet and relaxed. In just a little over 2 weeks of driving I've already noticed I'm not having to unsnap my tonneau cover and fill the fuel cell as often. This GV is on the top of my very long list of modifications and improvements.

My wife often likes to remind me of all the money I've poured into my Ranger project, since I retired from my career as a truck driver, just over a year ago. She is right, no expense has been spared on the re-make of this fun little truck. The Gear Vendors is worth every penney and will eventually payback in fuel savings and less wear and tear.

So thanks to all who helped out in sales, and Mike in tech, for your assistance, and thank you all at Gear Vendors for such a fine product. Feel free to use my letter or pictures if you care to.


Brimfield, MA