TECHLINE Harley-Davidson Motorcycle Transmissions

Part III: Shifter springs, shifter forks & other shifty things – by Donny Petersen

This month in American Iron Harley magazine we continue with an excerpt from Chapter IX of Donny’s Unauthorized Technical Guide to Harley-Davidson 1936-Present, Volume III.  (Some content has been altered to fit AIM’s style and format.)

The five-speed transmission shifter shaft lever (#34084-86; #34084-86A) is located outside the transmission case, near the top and front of the left side. This lever is connected to the external shifter linkage, which is activated by the shifter lever near the rider’s left foot. This shifter lever’s shaft extends through the transmission case and its appendage is part of the shifter cam pawl (#34086-79) assembly. In between the case and pawl sits a plate (#35068-79) and the shifter shaft return spring (1979-92: #34087-79; 1993-2000: #34087-79A). The function of the spring is to return the foot shifter to the center position between the upshift and the downshift positions. This spring is the reason the shifter does not stay down after downshifting. The shifter may stay up after upshifting, but gravity will probably bring it down even if the spring is broken.

The function of the shifter shaft return spring (arrow) is to return the foot shifter to the center position between the upshift and downshift positions. This spring is the reason the shifter does not stay down after downshifting.

Shifter Shaft Return Spring
The shifter shaft return spring sits above the churning gear clusters beneath. Unfortunately, the early version of this spring has a nasty habit of breaking. When the spring breaks, it has nowhere to go but down into the meshing gears. Pieces of the spring may make their way down past the gears and lie harmlessly in the oil bath underneath. However, sections may lodge between the gear teeth, severely damaging or knocking them off their gear. It’s possible that nothing will give way until the five-speed transmission case cracks, but, in my experience, something else will smash up first. It’s a different story with four-speed transmission cases, as they can crack when debris falls between gear clusters.

You’ll know you have a problem if the foot shifter will not automatically return to its center position after up- or downshifting. Furthermore, if the spring’s broken pieces fall into the gears, the rear wheel may suddenly lock up for an instant and then break loose again when parts break, dent, or bend inside the transmission.

The problem is that the early springs on the shifter cam support have a sharp turn or bend, which creates a stress point and allows pressure to concentrate there. The constant back-and-forth, up-and-down movement as the gear shifter is shifted eventually breaks the spring at the sharp bend. This problem was corrected in 1993 with a stronger and more durable shifter shaft return spring. A rounded bend replaced the former sharp bend, which distributes the pressure more evenly throughout the metal, eliminating the weak spot. The newer version spring serves the five-speed well up until the demise of the Evolution in 2000 and through the Twin Cam years until the introduction of the Cruise Drive six-speed transmission introduced on the 2006 Dyna models and all Big Twins in 2007.

To get the rest of this story visit GreaseRag.com and pickup the March 2011 issue of American Iron Harley magazine.