Double Shear Selector Rod
for most BMW models
Please [ CLICK HERE ]
for available applications.
While producing a "short" shifter, our more important goal
in improving the BMW shifter assembly is to increase the precision and
smoothness of the overall operation.
One significant wear area that has never been addressed
previously is the wear and ovalization of the linkage connection points
at the transmission and the shifter's lower pivot. (figure 1)
In the original BMW design, the connection at both ends has a large
injection-molded plastic bushing. We already know how badly plastic wears
in an automotive application, and
these areas are not an exception. The design of the selector rod has a
pin at 90 degrees 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.
(figure 2) The fig. 2 image shows a selector joint that has
approximately 25K miles of use.
The 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.
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). (figure 4 and 5)
The DSSR redistributes the torsional forces from the pin/bushing
interface to the complete face area on both sides of the selector
joint. (figure 6)
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. (figure 7)
In-gear "free play" is reduced to approximately 10mm
total when used with a UUC EVO3 shifter. (figure 8)
The original BMW shifter and all other 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, whether
original BMW or other-brand 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).
While there are other replacement selector rods sold in the
aftermarket (including "no tolerance" brass and "heavy" selector rods),
none of them will get rid of the slop and "free play" in the BMW
shifter assembly. These alternate products are not actually improving
the 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 a new BMW part, and will develop the same
slop within a few thousand miles. (figure 9)
Note: currently available DSSR fitments are suitable for UUC
EVO 3-series shifters, original BMW shifters, and all aftermarket
CLICK HERE ] for available applications.
? 2004-2012 UUC Motorwerks