Six Full Gears of Smooth, Quiet Power

Ever since Baker Drivetrain hit the scene a decade ago, the company has been making waves in the Harley market-not just waves, but monster waves. Taking what he had learned as a senior project engineer at General Motors overseeing manual transmissions, Bert Baker applied this knowledge to his personal bike to make it run more smoothly. Bert’s hard work paid off in the form of Baker’s revolutionary six-speed overdrive transmission (OD6). Over the years this transmission became standard fare on many custom bikes, not to mention thousands of Harleys whose owners tossed their stock gears in order to get the benefits of running an overdrive gear, which afforded them a smoother, quieter ride while dropping the rpm of the motor.

Anyone who knows Bert knows he just can’t stand still. If he’s not tinkering with a new project, he’s figuring out how to make an existing one better. Baker’s DD6 (Direct Drive six-speed) is a result of Bert’s constant search for improvement. Just as the original OD6 was revolutionary in the ’90s, the DD6 is even more so today.

The OD6 was designed to give riders an additional Sixth gear with an .86:1 (a 14-percent reduction) ratio while still maintaining the same stock gear ratios (1-5) as the Harley transmissions. The only downside to this was that, based on the transmission’s design, the Sixth gear was only about 92-percent efficient. While 92-percent efficiency was standard for this type of application, Bert knew he could come up with a better way to put more power to the pavement, and that’s exactly what he did with the DD6.

By redesigning the internals of the transmission, Bert was able to effectively remove a pair of gears from the operation of both Fifth and Sixth gears. By doing so, there is less horsepower lost in the transmission, resulting in higher efficiencies in the 99-percent range. That, coupled with the design of the helical-cut Fourth, Fifth, and Sixth gears, results in much smoother and quieter meshing of the gears, making for an even more pleasant riding experience. Although this concept makes lots of sense on paper, there was still one hurdle Baker needed to overcome. By going with a 1:1 Sixth gear, the benefits of reducing rpm while at highway speeds were lost. In order to restore this benefit, Bert decided to change the ratio of the stock primary drive. He did this by replacing the stock compensator sprocket with a new, larger 28-tooth sprocket, and this, coupled with a new primary chain and redesigned chain tensioner, gave the new DD6 the same ratios as the older OD6 while giving it greater efficiency. Simply put, Baker over-drove the primary instead of the transmission.

The DD6 is designed to fit perfectly in place of the stock H-D transmission (both Twin Cams and Evos), and its interface to the inner primary is identical to a stock transmission. Baker makes the DD6 in styles to fit Softails, FLTs, FLHs, and Dynas, as well as customs. The transmissions are available in multiple finishes, including raw, polished, chrome, and wrinkle black. The unit we are installing is designed for an Evo Softail and has a wrinkle-black finish (MSRP: $3,195). Baker also makes a builder’s kit consisting of all the same components with the exception of a new transmission case, saving the bike owner roughly $700.

Since our motor was still sitting on the bench, we needed to install it to the frame in conjunction with placement of the new transmission, and then the two could be coupled to the primary prior to alignment of the entire drivetrain-an important step.

Depending on what stage of completion your bike is in, it may be necessary to complete all of the following steps, or possibly only some of them. Next stop, Bennett’s Performance.