Justin Cesler
January 25, 2011
Photos By: Steve Baur

Whether you're a seasoned Mustang modifier or are just now enjoying the ownership of your first classic Mustang, you are probably familiar with one of the golden rules of tinkering: For every positive action, there is usually an opposite and equally negative reaction. Take for instance that new camshaft you have been eyeing. While it certainly will give you more horsepower, torque, and parking lot credibility, it won't do so without costing you a certain amount of driveability or gas mileage. Or, how about a new ring-and-pinion? While a set of 4.10 gears will make getting off the traffic light a blast, the downside is the inevitable loss of gas mileage and the wear and tear of sustaining higher rpm while cruising. Of course, for every rule, there is an exception. In our particular case, we're talking about automatic transmissions, an essential piece of your driveline that can normally be upgraded without suffering any decrease in performance or enjoyment. In fact, with many new cars coming with six-speed manual and automatic gearboxes, it's hard to argue with the theory behind adding gears to any retro ride.

Case in point, our '70 Mustang coupe. Powered by a 302 and a C4 three-speed automatic transmission, the '70 is a real driver, although it has recently sat dormant due to a destroyed transmission. When we went searching for rebuild options, we immediately thought of ditching the C4 for an AOD unit, which could be built just as strong, while also giving us an overdrive gear, allowing for a more modern cruising experience, an increase in gas mileage, the ability to stay in our engine's powerband longer with each shift, and the option to upgrade our rearend gear later, without making our Mustang undriveable on the street. Now, we must be honest, there is one downside to converting your C4 to an AOD and that's the amount of time and money you have to spend scouring the Internet to find the right parts.

Enter Monster Transmission and Performance of Brooksville, Florida, a company dedicated to providing some of the best transmission rebuilds on the market. After seeing a need for simple, turnkey overdrive transmission conversions, the crew at Monster sat down and compiled a virtual nut-and-bolt list of everything needed to complete this swap. With one call to the folks at Monster Transmission, we were set up with everything we needed for the swap, including a 450hp-capable AOD transmission, a new torque converter, a flexplate, a block plate, and all of the required linkages. Inside the Mega Monster AOD, there are a plethora of upgrades, including Alto Red Eagle clutches with Kolene steel friction plates, a one-piece input shaft, and a vehicle-specific shift recalibration kit, which Monster tailored to our exact needs.

Of course, the extra horsepower capabilities of the Mega Monster were a bonus and the upgraded shift feel will make for excellent part throttle and wide-open shifts, but the real magic here is in the overdrive. With a 0.67 Fourth gear ratio, Monster claims customers will see a 30- to 40-percent increase in gas mileage over a C4, which, depending on how much you drive your classic, will basically pay for the transmission in no time. Now, we know you're interested in seeing how this conversion is done, so follow along with us as we equip our '70 Mustang coupe with a Mega Monster AOD. We promise it will be worth the upgrade!

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