Mustang Rear Lower Control Arm Frequently Asked Questions
Why change from the stock Mustang rear lower control arms?
Because the stock lower control arms were designed for a grocery-getter, not a performance car. One of Ford's main goals when they designed the rear suspension was to avoid complaints about NVH (Noise, Vibration, Harshness) from little old ladies. As performance enthusiasts, we have very different goals.
What do the rear lower control arms do?
Rear lower control arms, along with the upper arms, control axle rotation.
All of the forces that accelerate the car pass through the rear lower control arms: The tires rotate on the pavement, moving the axle forward. The axle pushes on the rear lower control arms, moving the rest of the car forward. The control arms, and their bushings, must withstand those forces.
What's wrong with the stock control arms?
In stock form, the rubber bushings in the control arms allow excessive deflection that prevents the rear axle from maintaining its correct position under the chassis. The axle is allowed to shift forwards, backwards, and sideways under the car. This is the primary cause of wheel hop, and leads to poor traction and poor handling.
The stock arms are made of stamped steel. That style of construction is very cheap for mass production, but it does not make for a rigid control arm. Deflection of the steel arm contributes to wheel hop.
Instead of improving the control arms, Ford's attempted solution to stop wheel hop was to add the quad shocks (the two horizontal shocks mounted behind the rear axle). These shocks damp out oscillation and reduce the axle rotation allowed by deflection of the rubber bushings. That rotation (axle wind-up) leads to wheel hop.