The Goal
While producing a "short" shifter, UUC’s guiding goal in improving the BMW shifter assembly is to increase the precision and smoothness of the overall operation.
The Problem
One significant problem area is the wear and ovalization of linkage connection points at the transmission and the shifter's lower pivot.
In the original BMW design, the connection at both ends has a large injection-molded plastic bushing. Plastic wears greatly in automotive applications, and these areas are not an exception.
The design of the selector rod includes a pin at 90° to the main rod, which exerts a tremendous amount of leveraged force on the selector joint bushing from one side (known as a single shear force). The result is a steady deformation of the bushing, resulting in looseness and slop in the entire mechanism.
Looseness and slop are magnified by the leverage-multiplication effect of the shift lever itself. The result is an in-gear shifter "free play" of 3/4" and up to 1" in either direction, over 35mm total.
The Cure
A temporary fix is to simply replace the selector joint. Unfortunately, this is only a temporary fix as the new joint's bushing will exhibit the same rapid deformation. To permanently fix this, a change in the fundamental design of the pivot is required, changing the assembly to a double shear system with the UUC Double Shear Selector Rod (DSSR).
The DSSR redistributes the torsional forces from the pin/bushing interface to the complete face area on both sides of the selector joint. By taking advantage of the strength of steel in the DSSR and the body of the joint, the problem of deformation is eliminated and the movement of the selector rod correlates directly to movement of the selector joint - the only "free play" movement remaining in the shifter assembly is from within the transmission itself. In-gear "free play" is reduced to approximately 10mm total when used with a UUC EVO3 shifter.
OEM and aftermarket shifters (except UUC, which uses deformation-free bearings) contain a plastic bushing similar to the selector joint, and the exact same wear and ovalization causes those shifters to get sloppy. The DSSR permanently fixes these shifters also. The DSSR is compatible with all brand shifters, OEM BMW or aftermarket. When used with the original BMW shifter or other aftermarket shifters, the amount of "free play" will be greatly reduced but varies by shifter (flexation of the shifter shaft contributes to the total "free play" travel).
No Other Solutions.
While there are other aftermarket replacement selector rods (including "no tolerance" brass and "heavy" selector rods), none will get rid of the slop and "free play" in the BMW shifter assembly. These alternate products are not actually improving shift feel at all, but are simply rods with alternate geometry (either bent or twisted), an accommodation to make the "universal fit" aftermarket shifters fit properly.
These other aftermarket shifters, even with their "heavy" selector rods, will still be as sloppy as the original BMW shifters they are replacing. While the throw may be shorter, the precision of the assembly is no better than OEM, and will develop the same slop within a few thousand miles.