Shown below is a brand new E46 M3 replacement floor and cross member (aka push rod) – both virgin, never having been torqued before – with AKG SF469 Poly 90A subframe bushing installed on the left side, and factory bushing on the right side, to show a comparison of how they are fitted. The unit is upside down with E46 floor sitting on bench, for a clearer view. In this photo, the cross member is only torqued to the floor. The ears are not yet torqued down. As you can see, the height as installed on each side is the same. The AKG bushing is touching both the cross member and the floor of the car. The factory bushing however, shows a gap as installed (see photos 3 and 4 for more information).
The next photo shows the bottom view of the AKG bushing fully installed, sitting in car frame. You can see here that the AKG bushing is longer than the AKG sleeve (10.5mm). The AKG bushing was designed with maximum pre-loading in mind, in order to eliminate most of the damaging vertical movement, and the sleeve is only used for locating and centering the subframe into the floor mounting.
We do not use a factory length sleeve, as that would cancel the effect of our design. Our design is meant to spread the load to a wider area (80mm). If we used a factory length sleeve, the AKG poly 90A bushing would instead behave like a factory bushing with the main torque point being the center sleeve (30mm), which would allow the same undesired maximum vertical movement as with the factory bushing. This undesired vertical movement would contribute to the hammering effect under acceleration, causing the top front bushing to mushroom. (That mushrooming affect would only apply to the softer Poly 90A material used to give more comfort for street use. Our Poly 75D or solid aluminum bushings would not mushroom, since these hard materials are not compressed by torqueing.)
Close up of factory bushing as seen installed in photo 1. Shows the significant gap between the factory cross member and the original factory bushing.
Close up of factory bushing as seen installed in photo 1. We used a filler gauge (.70 filler gauge = approx. 2mm) to measure the gap between the factory bushing and the new cross member. As you can see the ears must be compressed by 2 mm to even touch the factory bushing. This shows that insignificant compression of the ears to touch the bushing is not an issue. The cross member does its job as a double sheer support preventing horizontal subframe movement.
Please see our Install Page, and always use proper torque values when installing your bushings!