Mopar Stock Suspension Upgrades - Handle It!

Control Arms

The factory control arm design works pretty well as is, but there is always room for improvement. The original lower control arm design is an unboxed U shape, which can be twisted out of shape by a stiff antisway bar. We feel that boxing the lower control arm when using big antisway bars seems like a good idea. The upper control arms are a fairly simple design stamped out of steel. This design works OK for most applications, but one downfall is that the threads in the arm are easily damaged when replacing the upper ball joint, so most original control arms are worn out by now. Stamped replacement upper control arms are available in the aftermarket, but for serious performance it is probably best to go ahead and purchase a set of fabricated upper arms. The fabricated upper arms are designed to provide more caster and camber than is available from a stock arm, and the threaded sleeve used in most fabricated arms is much more robust than the stock design. If you are determined to keep the factory upper control arms, and need to get more camber, Moog makes an offset bushing to help. The offset bushing locates the center hole of the bushing off center to "move" the control arm farther, in order to gain more camber ability. Caster angle means that the pivot points of the steering (ball joints) are angled such that if a line is drawn through them, the upper ball joint is behind the lower one. The purpose of this is to provide a degree of self-centering for the steering--the wheel casters around so as to trail behind the axis of steering. This makes a car easier to drive and improves its directional stability (reducing its tendency to wander). Excessive caster angle will make the steering harder less responsive, but in racing, large caster angles are used to improve camber gain while cornering. Camber angles alter the handling qualities of a suspension. Negative camber will improve the grip of the tires when cornering. This is because it places the tire at a better angle to the road. Another reason for needing negative camber is that a tire tends to want to roll over itself while cornering. This effect is only true for the outside tire during the turn; the inside tire would benefit most from positive camber.

On the other hand, for maximum straight-line acceleration, the greatest traction will be achieved when the camber angle is zero and the tire's tread is flat on the road.

Some of the aftermarket control arms are adjustable to increase the available caster/camber angles, while others use relocated pivot points to change the front suspension geometry. There are a lot of options for upper control arms, so a little bit of Internet research is probably a good idea before you place the order.

Steering Linkage

There are a few tricks that can be used on the steering linkage to improve the feel and precision of the steering. If you have a manual steering box, you can change to a faster ratio box using either a 16:1 gear set or a 20:1 gear set. These quick ratio gear sets can be hard to find, so some searching might be required. The quick ratio steering box will increase the steering effort, so be careful if you have a nose-heavy car and wide tires.

If you are planning on higher cornering speeds, then it is always a good idea to reinforce the steering box mounts on the K-frame. Any flex in this area reduces the responsiveness of the steering system. One last idea is to swap in the larger tie rod adjuster assembly from a C-Body car. The C-Body cars used larger 11/16-inch tie rod ends, which are twice as stiff as the original 9/16-inch units. This is a bolt-in swap, and as an added benefit, the C-Body tie rod assembly is often less expensive than the A-, B-, or E-Body part.

Wheels, Tires and Chassis

While the suspension is the primary focus of this article, the suspension does not act on its own. The tires connect the suspension to the road, while the chassis provides the mounting points for the suspension. Reducing the weight of the wheels will reduce the load on the shock absorbers, and make it easier to control wheel movement over rough sections of road. Tire width and aspect ratio will also have a dramatic effect on the car's handling. Mopar muscle cars were originally designed around tall, skinny, bias-ply tires. These tall tires were fairly soft and tended to roll over and distort while cornering. Replacing the original tires with wider, low-profile tires is one of the first steps towards improved performance.

The chassis also plays an important role in how well the suspension works. The Chrysler engineers designed the original unibody chassis to complement the OEM springs, shocks, and tires. Once the suspension is upgraded, the chassis will be unable to properly handle the loads placed on it. At some point, the springs and shocks become stiff enough to distort the chassis. Rather than compressing just the springs and shocks, the sheetmetal and frame will also start to deflect under the loads of heavy cornering. Photos of stock body NASCAR racers from back in the '70s will clearly show how much extra bracing was used to support the shock towers and K-frames. The guys who built those old race cars understood that they wanted the chassis to be rigid and the suspension to be compliant. That was good advice then, and it is still good advice today.

Summary

The Mopar torsion bar and leaf spring suspension was an excellent design. Even after more than 40 years, the original design is holding up well. A careful mix of replacement and aftermarket parts should allow any of the Mopar muscle cars to perform excellent on the street as well as at the track.

Rebound meters how fast the fluid is returned to the original reservoir, or how fast the tire can go to full or partial droop. If you have too much rebound pressure, the wheel doesn't go back down after the compression cycle. If it can't go back down quickly enough, and you're hitting continuous bumps, the car actually lowers itself and can eventually bottom out the shocks.