Here at Mopar Muscle we've been drag racing our cars nearly as long as we've been driving, and, like any true enthusiast, we want our race cars to be pure Mopar. If there's one thing we hate to see at the track, it is a two-speed transmission in an otherwise great race car. We've heard the arguments: the two-speed automatic is considered more consistent for bracket racing; it takes abuse well; and it has a ton of aftermarket support, but whether completely aftermarket or not, the two-speed is still a brand-X transmission. The reality is most race applications, which utilize the two-speed automatic, would do just as well, or better, with a properly prepped TorqueFlite. The advantage is one more gear for torque multiplication allowing more leeway when it comes to converter selection, as well as keeping a heavier race car in its peak power range all the way down the track. The 727 can certainly handle a ton of power and is a very consistent performer, as we've shown with our Super-Pro 68 'Barracuda. If your combination is one that overpowers a race TorqueFlite (which for the record takes way upwards of 1,000 hp), you may be in the market for a Lenco or other pure race transmission. If you're like us and enjoy racing your Mopar with as many true Chrysler parts as possible, we'll show you how to build a TorqueFlite to handle your power and maybe even shave a little off your e.t. in the process.
If you follow drag racing history, you know the TorqueFlite automatic, much like Chrysler's A-833 four-speed, has a reputation for strength and durability. The 727 is a relatively simple piece when compared to other automatic transmissions, and its strength is a function of that simplicity. We've put stock TorqueFlite transmissions behind big-blocks pushing upwards of 600 hp and found they not only survive, but perform quite well. Pure race applications, however, will find the weak link of any combination, and the transmission is no exception. Planting 700 or more horsepower through a set of sticky rear tires in a 3,100-pound door slammer will require some transmission modifications. We're not talking about any high-tech machining or super expensive aftermarket parts, just good, solid replacement parts for what we consider the weaker areas of this tough transmission. Our combination is slated for our '68 Barracuda, which races in Super-Pro (electronics) class, as well as seeing some duty in the local Quick 16 races. To be competitive in Super-Pro, a delay box has pretty much become a requirement, so a transbrake valvebody will be utilized for this build. You don't have to use a delay box to use a transbrake, but you have to use a transbrake to run a delay box. We've never been big fans of delay box racing, but when we put this combination together, it ran too quick to race in the foot-brake classes. Not the type to purposely slow our car down, our choice was made for us, so the transbrake and delay box will be installed, making the car more consistent and competitive.
For those of you unsure how a transbrake works, the theory is really very simple. The transmissions valvebody is modified with an electric solenoid, which will actuate the reverse band of the transmission. When the car is staged at the starting line in low gear, the transbrake button is pushed, engaging the reverse band. This basically locks the transmission in first and reverse, and the engine can be revved to the limits of the stall converter or launch rev limiter without moving the car. When the button is released, reverse is disengaged, and the engine's power is all directed to first gear. The result is a harder, more consistent launch, though sometimes at the expense of drivetrain parts.
For our build we'll be using the TCI (pN 121900) transbrake valvebody, as well as several other trick parts to provide our car with a race transmission that will be dependable, consistent, and rugged. The TCI valvebody impresses us with its heavy-duty solenoid and solid construction, and will give us the fully manual reverse shift pattern that we need. TCI also offers this valvebody with a "safety neutral," which is an additional neutral position after third gear. This helps reduce engine wear that occurs during deceleration after a pass. We recommend this part for those of you running aluminum rods, as you'll get nearly double the life out of your rods. Our combination uses steel rods, and our shifter has no provision for an additional neutral so we'll stay with PN 121900.
Anytime you build a transmission for this kind of power and weight combination, there are several pieces that we consider mandatory. First is a bolt-in outer race for the overrunning clutch (also commonly referred to as the sprag). This piece is readily available from several manufacturers. We got ours from TCI. Next, you'll need to replace both the front and rear three-pinion planetary gearsets with four-pinion units. Rather than purchasing expensive aftermarket planetary gearsets, we set our sights on the salvage yards for these items. Chrysler actually put four-pinion planetary gears in many of their factory transmissions, so knowing where to look can save you a few bucks. The gearsets we're using came from a Winnebago motor home that utilized a '70 full-ton Dodge truck chassis. Finding the four-pinion planetary gears is somewhat hit or miss, but we've found that big-block truck transmissions from the late '60s through the late '70s are a good place to look.
The next item we consider almost mandatory is an aftermarket front clutch drum. The front drum takes the most abuse during first gear operation when torque multiplication is the greatest. If you've heard about or experienced a TorqueFlite grenading, it was likely caused by a front-drum failure. A factory steel front drum is adequate, but only if it has been checked for cracks by magnetic particle or dye penetrant inspection. Instead of taking chances with a factory front drum, we chose TCI's aluminum unit for two reasons. First, it is new and has already been inspected for defects that can cause failure, so we have peace of mind the drum will handle the abuse we'll give it. Second, the aluminum drum is lighter and frees up some ponies to send to the rear wheels, so we figure the TCI unit is money well spent.
Enough about theory, let's get on with the build so we can go racing. For our overhaul we enlisted the help of Tod Struck at Inline Performance Specialists in Bushnell, Florida. Tod has been a Chrysler specialist for more than 16 years and knows the TorqueFlite as well as anyone we know. He and his son are also avid drag racers and support several local Mopar racers with their transmission builds and chassis setups. We won't be covering the basics of transmission building in this article, rather highlighting the modifications required for a race transmission. For more detail on basic transmission building, refer to our "TorqueFlite Teardown" article in the November 2005 issue.