Double Shear Selector Rod
This part fits:
Z4M
Z4 3.0i
Z4 3.0si
NOT for Z4 30i
All kits include two DSSR pins, two "U" clips,
shims and grease.
The goal.
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.
The problem.
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.
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° 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.
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.
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.
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).
No other solutions.
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.
© 2021 UUC Motorwerks
