Transmission Weight Reduction - The Tranny Diet

Everything that has mass has a “moment of inertia,” the energy required to spin an object about its axis. The greater the moment of inertia, the greater the energy required. Two factors affect an object’s moment of inertia: mass and the distance of the mass from the axis of rotation. This means that a one-pound solid rod with a one-inch diameter will have a smaller moment of inertia than a one-pound disc with a 12-inch diameter. That’s about all the physics my brain can stand. Let’s move on.

The best way to make sure the horsepower produced by your engine makes it to the rear wheels is to reduce the rotating weight of the driveline to the absolute limit without sacrificing durability. And generally, because of gear reduction at the transmission and rear differential, the closer to the engine you are when removing rotating weight, the greater effect it will have on the car. That’s why a properly-built and maintained transmission can be a tremendous advantage on the racetrack.

When it comes to the Saturday-night level of oval-track racing, many sanctioning bodies require “stock-style” transmissions, which can have either three or four speeds. This severely limits the number of options available to the competitive racer. There are the normal junkyard options, Muncie and Saginaw, but those are getting extremely difficult to find. One popular solution is the T10 transmission, now being produced by Richmond Gear. The T10 was originally designed in the early ’70s by Borg-Warner and found throughout the ’70s and early ’80s in nearly every GM automobile with a manual four-speed.

The right to produce the transmission is now owned by Richmond Gear, which mainly sells it to racers and street rodders. It is lightweight and durable, but the gears are clustered into a single unit, limiting the racer’s options for customization. The T10 is also a four-speed, which is one more than most oval-trackers need for racing.

Where it’s legal, there are ways to improve the T10 for the Saturday-night circle tracker. Johnny Hightower, owner of Hightower Racing Transmissions, has been building custom racing transmissions for years. A longtime racer himself, Hightower’s work building custom racing transmissions isn’t widely known, but his client list does include some pretty impressive names. Three-time Hooters ProCup champion Bobby Gill races Hightower’s equipment, as does former ASA champ Gary St. Amant. Other customers can be found in All Pro cars, the Busch Series and Late Model race cars across the country. Recently, Hightower turned his attention to transforming the T10 into an oval-track monster. “I’ve been customizing Jerico transmissions for years,” Hightower says. “Jericos are great units, but they are built expressly for racing and aren’t legal in series that specify stock-style [stock outer case, usually] transmissions. That leaves the Richmond T10 unit, which is the only thing that is strong enough to be raced, still being built new and will fit within the rules.”

For years, racers who were lucky enough to have a Muncie or Saginaw three-speed in good working condition enjoyed an advantage—in terms of rotating weight—over racers using four-speed transmissions. Now Hightower has made the playing field a little more level with his three-speed version of the T10. Originally, he began with a completely stock unit and made all modifications himself. Now though, he has been able to work with Richmond to produce custom pieces exclusively for his use.

The first step is to cut down the cluster gear. Hightower’s redesign for the T10 includes completely throwing out the existing reverse gear, flipping the reverse idler around and using the first gear slider to drive reverse. Since the entire gear isn’t necessary, he cuts it down until it’s approximately only a half-inch wide. To minimize heat buildup Hightower actually cuts the gears off the cluster on a lathe instead of grinding the metal away. It requires more time and a lot more care with specialized tooling, but he believes the end result is worth it.

To match the new cluster gear configuration, Hightower also uses custom output shafts. Depending on what the racer’s rules will allow, he has one for use with roller bearings and another for the standard setup—the gears spin on the shaft with nothing but a film of oil to reduce friction. We did a very unscientific test comparing the roller-bearing equipped shaft with the standard unit. Without lubricant or any tension on either gear, a flick of the wrist sent the roller-bearing gear spinning two to three times longer than the gear spinning directly on the shaft. The motion is quite noticeably smoother.

“I’ve been adding roller bearings to transmissions for years and never had any trouble with failures,” Hightower says. “The more friction you have, the more heat buildup you are going to get. Neither is good for a transmission. Plus, when the gear and shaft heat up, they expand making them fit even tighter; that’s where I’ve seen galling problems. The bearings help reduce all of that. The transmission depends on oil splashing up between the gear and the shaft to provide proper lubriction; a roller bearing just requires less lubricant.”

Once all the various parts and pieces are properly chosen and cut down to Hightower’s specifications, the first option is to put all gears, shafts and shifter forks through a time-consuming polishing process. Hightower uses REM equipment and a special media mixture designed to reach even the tightest slots on the gears. Don’t even bother asking him about the fluids used, because all you are going to get in return is a sly smile. The polishing process cuts down all sharp edges—potential crack points—and smoothes all the surfaces to a mirror finish. When he’s finished, the gears look like they’ve been chromed.

Assembly is fairly straightforward. The reverse idler gear is cut down and flipped over, and even though it’s significantly smaller and lighter than the stock configuration, it still secures to the stock mounting points. Normally, the idler gear extends into the tailhousing, but a plug contains Hightower’s unit completely within the gear case. One note here: Hightower has significantly cut down the reverse gear. It can be used to back the car, but only very gently. For simply maneuvering the car around the pits, he recommends pushing the car whenever possible. (If you’ve ever had the opportunity to spend some time in the Winston Cup pits, you might have noticed the Cup guys doing the same thing. Reverse gear is weak in almost every full-race transmission.)

Overall, when Hightower has finished remaking a T10, the reverse gear is gone from the tailhousing, the idler gear is cut down, first gear (now reverse) is significantly cut down and the synchronizers and shifter fork are removed. And if the customer wants it, the tailhousing bushing is also replaced with a roller bearing to further reduce parasitic losses. It all adds up to approximately seven pounds of rotating weight removed from the transmission.

Second is used for a pit gear, third is the gear for restarts and fourth, of course, is for racing. Hightower sells a stock T10 three-speed for $1,450 and his polished unit with free-spinning roller bearings for $1,950.