Most street-style four-links are canted-bar systems that minimize the need for a lateral locating device, like a Panhard rod or Watt’s link. This design is generally more for simplicity and cost savings than it is for functionality. Regardless, a canted four-link still does not laterally locate the rear as precisely as a Watt’s link. Alternately, some street four-links use a Panhard rod, which does a better job locating the rearend than a canted four-link. The downside is that Panhard rods still allow slight side-to-side movement of the rearend due to the arc of travel that the Panhard rod follows while the suspension extends and compresses. The Panhard rod must rotate on a fixed arc relative to the body as the suspension goes through its range of motion. This arc creates dynamic side-to-side movement that gets progressively worse as the suspension travels. Another shortcoming of a Panhard rod is roll center migration. During suspension travel, a Panhard rod allows the roll center to migrate left to right, which affects the roll axis of the car. This inconsistency is due to the fact that a Panhard rod pivots from only one side of the body. A Watt’s link fixes the roll center location dead center, allowing the body weight to roll on it. As such, Watt’s links always remain true to center as each link is equal in length, pivoting from one common center. Moreover, the BMR Watt’s link has multiple vertical mounting points to provide roll center height adjustment as well. This is very helpful in tuning the roll axis of the car, which, along with the sway bars, dictates whether the car will understeer or oversteer through the corners.
One of the key features of BMR’s Torque Arm Suspension system—which includes a torque arm, coilovers, a Watt’s link, and lower control arms—is the ease of installation. Installing this system in place of a factory leaf-spring suspension is a bolt-in affair. There is no cutting, welding, or fabrication required to install our kit. The torque arm bolts to the rearend, and to a crossmember that attaches to the body mounts on the front subframe. The control arms mount to the original leaf-spring pockets on the body and to the leaf-spring mounts on the rearend. The shock crossmember requires drilling four holes in the rear framerails to secure the mounting position. However, the crossmember itself supports the load, not the boltholes. The whole setup can be installed and adjusted in a weekend.
The rearends in GM cars that came equipped with torque arms from the factory are prone to brake hop under hard braking on road courses. Fortunately, BMR has taken several measures in its torque arm design to address this issue. Brake hop under deceleration in third- and fourth-gen F-bodies is generally attributed to a flexible torque arm, a lack of shock valving, or excessive “plowing” under braking. These factors unload the rear of the car, which results in brake hop. People generally correct this through shock valving, running less aggressive rear brake pads, or tweaking brake bias. Similar to wheelhop under acceleration, other cures include removing the flex from the suspension components, sometimes altering the control arm geometry with relocation brackets, or upgrading to shocks with separate compression and rebound adjustments. In BMR’s torque arm kit, the torque arm itself is made from heavy-duty 2x3-inch tubing with 0.120-inch wall thickness. It is very difficult to bend this material so flex is minimal. Additionally, our control arms have multiple mounting locations to help cure hop during acceleration and braking. The shocks we recommend for our torque arm kits are the Afco double-adjustable units. If a car is experiencing any wheelhop under braking, removing a few clicks to soften up the rebound adjustment will typically neutralize the hop.