Front Knee

Control arms (also called A-arms or wishbones) are the primary suspension links connecting the wheel assembly to the vehicle's frame or subframe. This applies to front upper, front lower, rear upper, and rear lower control arms — the principles are the same regardless of position.

What's Included

The control arm itself. Depending on the listing, bushings and/or ball joints may be pre-installed or sold separately. Not included: opposite-side control arm, related ball joints or bushings (if not pre-installed), sway bar links, or mounting hardware.

Left vs. Right — Both Sides?

Control arms are typically side-specific. While it's not always required to replace both sides simultaneously, it's generally recommended since a control arm on the same axle has typically seen the same wear and stress. At minimum, inspect the opposite side before leaving it in service.

Bushings: The Key Wear Point

The rubber bushings at the frame end of the control arm are what most commonly wear out — causing clunking, vibration, and handling instability. Many aftermarket control arms come with new polyurethane or rubber bushings already installed. Verify before purchasing; bare arms without bushings require a shop press to install new ones.

Ball Joints

If your control arm has an integrated ball joint (pressed in), confirm whether the replacement includes the ball joint. If buying an arm without a ball joint, the old one may be pressable into the new arm — but this depends on condition and design.

Upper vs. Lower

• Front lower control arm — the primary load-bearing link; typically larger and heavier; more commonly replaced

• Front upper control arm — controls camber and aids articulation; fails less often but important for alignment

• Rear upper and rear lower control arms — serve the same geometric function at the rear; rear lower arms especially can be damaged in rear-end collisions

Alignment After Replacement

A wheel alignment is required after replacing any control arm. Control arm geometry directly determines camber, caster, and toe — all of which shift when the arm is replaced.

Front Spindle Knuckle

The front spindle or steering knuckle is the central upright at each front wheel that the hub, bearing, and brake components mount to, while pivoting on ball joints to allow steering. It's replaced after severe collision damage or cracking. Knuckles are side-specific. On many designs the ball joints press into the knuckle — a shop press operation. The wheel bearing and hub mount into the knuckle and are typically separate purchases; given the labor involved, replace the hub bearing at the same time. A front-end alignment is required after installation.

Rear Knuckle Assembly

The rear knuckle mounts the wheel bearing, brake rotor, and connects the rear suspension links. Knuckles are replaced after collision damage or cracking. Verify the casting matches your suspension design — many vehicles have knuckle variants between standard and performance/sport trims.

Front Knee

The front knee is the upright/strut-mount casting used on some independent front suspensions — effectively a combined knuckle and strut bracket. It is side-specific and replaced after collision damage; match the casting to your exact suspension layout, and align the vehicle afterward.

Front and Rear Leaf Springs

Leaf springs support the vehicle on trucks, vans, and some SUVs with solid-axle suspension, providing both spring rate and axle location. Used leaf springs are viable when the packs are straight (not sagged or broken) and the eyes and center bolt are intact.

Key specs to match: spring length (eye-to-eye), eye diameter, number of leaves, and spring rate. Spring rate determines load capacity — replacing a high-capacity pack with a lighter one reduces tow/payload rating.

Coil / Air Spring

Coil springs are the helical steel springs on independent suspension vehicles. Air springs (air bags) replace coil springs on self-leveling and air-ride suspension systems. Both are vehicle-specific for ride height, spring rate, and mounting diameter.

• Coil springs: Always replace in axle pairs — a new spring on one side and a worn spring on the other creates a height imbalance and handling asymmetry.

• Air springs: Fail from rubber cracking, bladder puncture, or fitting failure. When replacing, also inspect the air compressor and height sensors. Used air springs are viable but inspect the bladder for cracking and the mounts for corrosion.

Torsion Bar

Torsion bars provide spring rate by resisting twisting — found on older trucks and some SUVs. They're side-specific (left vs. right) and have an adjustment point for ride height. Bars rarely fail outright but can crack if severely overloaded. Match the bar diameter and spline count exactly.

Strut

The strut is a combined structural suspension member and shock absorber. "Loaded" struts come with the spring, mount, and bearing pre-assembled — the easiest installation. "Bare" struts require a spring compressor to transfer the spring from your old unit.

Strut mounts and bearing plates wear independently of the strut — clicking or clunking when turning on an otherwise functional strut often indicates a worn mount. Replace the mount whenever replacing the strut. Alignment is required after any strut replacement — the strut determines camber and caster.

Sway Bar / Stabilizer Bar

The sway bar resists body roll by connecting left and right suspension. Sway bars rarely fail outright — when replacing, the issue is usually worn end links or sway bar bushings rather than the bar itself. Verify bar diameter (thicker = stiffer) and mounting point locations. End links and bushings are sold separately and should always be replaced when the bar is removed.

Front Axle Beam

The front axle beam is the solid I-beam or twin I-beam front axle used on some trucks, locating the front wheels and carrying the spindles. It is replaced after a bend from severe impact. Match the beam width, spring perch locations, and spindle/kingpin design.

Suspension Compressor Pump

The air suspension compressor maintains pressure in air spring systems. When the compressor runs constantly or fails to maintain ride height, the compressor (or a leaking air spring) is typically the cause. Verify the compressor pressure specification matches your system — some vehicles use a chassis-mounted pump; others integrate it into the spring assembly.

• Replace springs and struts in axle pairs to keep handling balanced.

• Always perform a wheel alignment after replacing control arms, struts, or knuckles.

• When replacing a sway bar, strut, or spring, also replace the associated bushings, end links, or mounts.

• Match suspension parts by exact vehicle, trim, and drivetrain — sport and heavy-duty variants differ.