Adding a rear sway bar helps keep your musclecar flat in the turns; here's how to install one on a leaf-spring rear suspension car.
We have been making upgrades to the suspension system on our 1962 Ford Galaxie 500XL ragtop with the goal of creating a car that goes, stops, and turns like a late-model performance car. In this installment, we are adding a rear sway bar from Gearheads Cruiser Products.
Full-sized Fords from the 1950’s and 1960’s utilize a leaf-spring rear suspension system. Leaf springs play double duty; they not only suspend the rear of the car, they also locate the rear axle under the car. This means they have task of holding the rear axle in place laterally as well as front to back. The forces placed on a car when cornering at high speeds tend to make the body roll to the outside of the turn, especially when dealing with a heavier car like our Galaxie. Body roll offsets the load on the inside wheel and shifts it to the outside wheel, altering the traction levels of each wheel. This has a negative effect on the road-holding performance of the car. Sway bars, also known as anti-roll bars, are added to vehicles to combat this unwanted motion.
To understand how a sway bar works, it helps to visualize the relationship between the axle and the car body and frame. Without a sway bar, when a car enters a turn, inertia acts on the body and frame and tries to keep the motion going in a straight line. The wheels, axles, and steering gear are trying to turn the car in a new direction. If the car body were rigidly mounted to the axles, there would be no rolling effect of the body. However, because the body is suspended by springs, the body is subject to unwanted motion in the form of body roll.
A sway bar is a device that attaches the rear axle to the frame with the intent of minimizing the body roll effect without limiting suspension travel, effectiveness, or comfort. The challenge is to control the axle / body relationship only in one axis, when the axle twists longitudinally in relationship to the body, or when the body twists in relationship to the axle.
So how is this accomplished? A sway bar mounts to the frame and the rear axle using mounts that allow the suspension system to articulate and move up and down, but it introduces resistance when a twisting motion is encountered. When viewed from the side, a sway bar needs long arms reaching either forward or back between the axle and the frame mounts to so the axle can move vertically and “swing” on the sway bar. When viewed from the rear, the sway bar needs to anchor to the outsides of the axle and the frame using a short length to provide anti-twisting leverage on the axle.
One additional benefit of a sway bar is an increased amount of straight-line traction, as the presence of the axle mounts and frame mounts provides a secondary attaching point for the axle on the frame. This rigid link provides additional leverage helping to keep the axle in a vertical position, resisting the tendency for leaf-spring rear axles to rotate and wrap up the rear springs. Spring wrap is a primary cause for wheel hop, a loss of traction in leaf-spring cars.
The Gearheads bar measures 7/8ths of an inch in diameter and mounts with 4 D-shaped polyurethane bushings.
Installing the rear bar is simple, but it is important to keep the proper positioning of the bar. The first step is to locate the sway bar laterally on the rear axle housing and tack weld the mounts in place. Keep in mind that the Ford 9” rear axle housing’s large center is not perfectly centered under the car, so it is best to measure the mounting points from the leaf springs inward.
The next step is to temporarily mount the sway bar on the rear axle mounts, and then locate the proper mounting points on the frame for the supplied brackets. This is best accomplished with the car at its driving ride height, as the sway bar needs to operate without binding. With the wheels on the ground, install the front mounts on the bar and swing the front of the bar up to where it meets the frame. Mark the location on the frame.
The Gearheads mounts are steel plates containing threaded holes. The mounts attach to the frame, and then the sway bar bushing mount bolts to it. This is a nice feature, as it forms a much more rigid mount than an end-link type mount, and the threaded plate ensures that the bolts will not pull out of the frame.
You have to drill or cut two ½-inch holes in the frame where the mounting plates weld to the frame to allow the mounting bolts to pass through the plate and frame. Use the plates as templates for the holes. Then you can weld the mount plate to the frame.
Next, install the sway bar on all the mounts, but do not tighten the bolts until the car is back at ride height. If everything looks good, finish welding the mounts on the axle and paint all the mounts to protect them from rusting. Tighten the bolts with the car back on the ground.
With your new rear sway bar installed, your rear leaf spring suspension system will be less prone to wheel hop and body roll, bringing your old ride one step closer to handling like a new Corvette!
FOLLOW-UP After driving the car with the rear bar installed, we're angry we didn't do this swap sooner. What a difference! The car handles ALOT better... it's flatter in the turns, and traction is improved as the rear bar doesn't let the springs wrap as much. This was a great swap!
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