These diagrams help illustrate what I’m talking about.
When the car accelerates, it has to push on the control arm through the bushing. It has to compress the bushing to its limit before it can push the car. Ditto for braking.
Those voids in the OEM bushing you saw earlier allow the control arm to articulate to the left and right about the bolt it mounts to. But it’s still rubber, and thus it still acts like a small spring that must be compressed before transmitting a force. The spherical bearings don’t have this problem, as they are free to articulate completely.
To remove as much slop as possible in Project Mustang’s rear suspension without also making the car painfully uncomfortable to drive on the street, we turned to BMR Suspension.
BMR has a wide range of control arms for the S197 Mustang chassis, ranging from inexpensive and lightweight “street” arms featuring polyurethane bushings to “full-race” adjustable arms featuring spherical bearings and Heim joints. Although the full-race arms would clearly perform the best, I didn’t want to completely compromise Project Mustang’s street manners, so I decided to test out BMR’s “combination” arms.
Seen here next to a stock control arm, BMR’s combination lower control arms allow adjustability and greatly reduced slop through the use of a spherical bearing on the axle side. The polyurethane bushing on the chassis side still helps prevent too much NVH from transmitting into the cabin.
BMR’s combination arms use a Heim joint on one end and a polyurethane bushing on the other. Through a lot of testing, BMR has found that replacing the bushing with a spherical bearing only on one side allows a huge increase in performance without sacrificing much NVH isolation. To completely transform the rear suspension, BMR sent us their lower and upper control arms and brackets, panhard bar and brace, and strut tower brace.
The first part of the ensemble was BMR’s nicely-designed strut tower brace, which uses two separate bars in a triangular configuration to provide maximum chassis stiffness:
There is some debate as to the efficacy of strut tower bars on the S197 chassis. However, I have found that they provide a slightly more confident feeling over bumps, surface imperfections, and any time the front end’s suspension is compressed.
The next stage of this installation involved the lower control arms, adjustable relocation brackets, and panhard rod and brace. You can see that each of these has a polyurethane bushing on one end (the chassis side) and a spherical Heim joint on the axle side.