Synchronizers perform the task of equalizing the gear speeds to the mainshaft speed. Blocking rings fit between each gear and synchronizer hub. They also have beveled teeth on their outer diameter that are identical to the dogs on the speed gear and a cone-shaped taper on their inner diameter. The blocking ring taper fits over a similarly shaped tapered surface machined into the side of the speed gear. As the slider is moved to engage a gear, spring-loaded shifter plates that fit inside slots on the synchronizer hub move with the sliding collar and push against the blocker ring, causing it to wedge against the tapered gear face. The speed of the freewheeling gear is brought into equilibrium with the mainshaft and synchronizer hub, and the shift can be completed.
How It Breaks
Now that we've gone over how it works, we can address how it breaks and how to make it better. As you can imagine, the blocker rings, sliders, and dog teeth take the harshest beating, especially under the sloppy shifting of a ham-fisted owner. But the parts that break are usually gear teeth and shafts. When a gear is selected, the dogs of that gear are encircled completely by the sliding collar, and power from the engine is spread out over a wide area--not so much with the gear teeth, however. The cluster gear and driven gears mesh in a relatively small area of contact--that's why the gear teeth will often break before the dogs are sheared off.
 Tremec's new T56 Magnum was...  Tremec's new T56 Magnum was designed to handle much higher horsepower and torque numbers than the standard T56. |  Wider gears in the T56 Magnum...  Wider gears in the T56 Magnum (left) are made possible by laser-welding the dog teeth to the gear face. |  This is a triple-cone synchronizer...  This is a triple-cone synchronizer assembly in a T56 Magnum. From left to right: dog teeth (that are welded to the gear), two synchronizer cones with an organic facing, a blocker ring, and a synchronizer hub and slider assembly. |
There are a few options to solve this breakage problem: Use harder steel to make the gears, make the gears bigger or wider, or reduce the pitch of the gear teeth. Some of these options are more expensive than the others, but the best option for all-out performance is to do all three. That's where we move into the high-performance transmission market.
The T56 Magnum has a much...
The T56 Magnum has a much larger input shaft and bearing (right) than the standard T56.
OE Plus
OE transmissions are a series of compromises made to allow quiet operation, smooth shifting, and long life. Unfortunately, these characteristics can make for clunky operation at the racetrack or worse yet, a box of ugly metal chunks when you put a lot of power to it. Tremec has just released a stronger version of the ubiquitous T56. Dubbed the T56 Magnum, it is filled with a number of improvements gleaned from years of R&D, racing in the American Le Mans series, and working with the OEs designing transmissions to go behind newer and more powerful engines in the Corvette Z06 and ZR1, Cadillac CTS-V, and Dodge Viper.
We discussed these improvements with the guys from Tremec. Product engineer Kevin Ryan told us one of the first improvements made was to increase the size of the input shaft and upgrade all the bearings in the box. The input shaft bearing is now nearly twice as large as the original T56, and all the bearings are made of better materials. Next, they switched to a proprietary blend of 4615 steel, a high nickel and molybdenum alloy that is stronger than stock but still easier to machine than the ultrahard 9310 steel used in most all-out racing boxes. The 4615 steel is used throughout the box--all the gearsets and shafts are made from it.
The gears in the T56 Magnum are wider than those in the T56. "That was a challenge," Ryan says. "We had to put bigger gears inside a case that was the same size as the original design." To accomplish this, Tremec changed the way its driven gears are manufactured. Most gears are forgings that include the dogs and the tapered cone that is engaged by the synchronizer blocker rings. All of these things need to be wide enough for the cutting tools to fit around those various surfaces to machine them properly. In the Magnum, two-piece gears are used. The gears and dogs are separate forgings that are laser-welded together. They fit tighter because they do not have to design in extra space for machining tool clearance. This tighter fit means a wider gear can occupy the same space.