Maximum Motorsports MM Aluminum Rack Bushings (MM K-Member)

Maximum Motorsports has reinvented the steering rack bushing!
Exchanging the stock rubber steering rack bushings for solid aluminum bushings has long been known to be a fundamental step towards improved steering response. Rubber bushings, and to a lesser extent urethane bushings, allow the rack to move sideways, relative to the K-member, before any steering input begins to move the tires. This results in slower steering response than is desired for a performance car. Solidly mounting the rack with aluminum bushings eliminates rack movement relative to the K-member, and improves steering response. Along with improved turn-in, the car will maintain a more precise line through a corner, and require fewer steering corrections.

In some instances, along with the improvement in steering response, comes an unwanted side effect”steering chatter at low speeds. Chatter can be caused if the steel steering rack binds up inside of the cast aluminum steering rack housing. This binding (binding means a resistance to moving freely) can happen if the rack housing is twisted when the rack was solidly attached to the K-member through solid aluminum bushings. Twisting can occur if there are irregularities in the steering rack housing, or in the two rack mounting surfaces of the K-member.

Stock K-members are made from stamped steel, and always have some irregularities in the two rack mounting surfaces. The two rack mounting surfaces are never flat, nor even in the same plane. This may be acceptable when soft rack bushings are used, but with rigid aluminum bushings it can cause the aluminum rack housing to twist, resulting in steering chatter. For those experiencing steering chatter, the only solution until now was to swap the aluminum rack bushings for softer rubber or urethane bushings. Unfortunately, this also meant a step backwards in performance. While urethane rack bushings allow only one half of the movement that rubber rack bushings allow, they are obviously not as rigid as aluminum.

MM has designed a new steering rack bushing that retains the benefits of a solidly mounted steering rack, but also prevents the twisting that can cause chatter. The MM Engineering Teams new design uses a spherical washer to accommodate the irregularities in the K-member surface, while still providing a solid mounting for the steering rack.

MM K-members have large flat areas where the steering rack mounts, so there are no surface irregularities. However, there may be irregularities in the steering rack housing itself, and the result can be binding of the rack motion, and steering chatter. Because MM K-members have a crush sleeve welded in place, we developed a completely different steering rack bushing than what we designed for the stock k-member.

This all-new bushing design allowed us to provide features that are not possible for a bushing that would be used on a stock k-member. These bushings for the MM K-member let the steering rack be installed in any one of five possible vertical locations. The center position places the steering rack in the stock location. Two different offset positions are possible: 1/4" offset and 3/8" offset. The offset positions can be used to either raise the steering rack, reducing the height of bumpsteer spacers used at the steering arms; or to lower the rack, providing clearance for oversized oil pans.