Transmission

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Over the years, Buell and Harley-Davidson transmissions have become smoother shifting and quieter, which has made the majority of riders happier. The first XB transmissions changed to a smaller gear pitch to increase contact patch and reduce noise. In 2006, the XBs switched to a helical cut gear set, which again reduced noise and made shifting a bit smoother. Even though the latest transmissions work well for most XBs, I didn’t want risk excessive axial loads that the helical transmission design could generate under high power, and I knew that I should upgrade the transmission how ever I could.

My stock straight-cut XB transmission held up to the 187hp and 150ft/lbs, but with the latest rebuild, I asked Mark at R&D Transmissions to set me up with the strongest possible setup. He put together an Andrew’s 2nd through 5th gear set and shafts, designed after the early Evolution Sportster transmissions with large tooth gears. To get the ratios I wanted, I retained the stock XB first gear set, which shares the large tooth gear pitch of the early XL transmissions.

The gears were annealed and heat-treated to a bit softer Rockwell C56. The gear dogs were back-cut with a straight-cut 1st gear back side dog to help shifting out of 1st during a wheel spin, and all of the parts were de-burred. Finally, everything was micro-polished and cryo-treated. This transmission preparation is the same as most drag-racers have done to maximize their transmission’s capability and improve the shifting.

To install the transmission in the 2007 XB cases, I had to make some modifications to properly align everything. The 2007 cases/transmission are set up for the helical gear set, and are machined specifically for a double-row angular-contact 5th gear main drive gear ball-bearing. Unlike the earlier transmissions, the bearing does not use a quad seal, so the main drive gear had to be grooved for an o-ring, like the helical 5th main drive gear. The inside face of the bearing also sits deeper in the case than the earlier style bearing, so I had .085″ machined off of the main drive gear lip that seats against the inside of the inner bearing race.

For proper alignment of the countershaft using the 2007 transmission bearings, I shimmed the left side of the shaft off of the left bearing by an additional .072″, using a machined Big Twin countershaft spacer. The fist picture is of the stock XB spacer and the second is of the modified, thicker Big Twin spacer.

The XB shift forks also needed to be modified to fit. The two XB shift forks that engage in the Andrews mainshaft gears need to be relieved to fully seat with the larger outside diameter of the fork groove.