Ford Focus ST Lower Control Arm Guide: OEM Replacement, RS Arm Swap, and Bushing Upgrades

ByKenji Alvarez

What Actually Fails on These Arms

The front lower control arm on the Mk3 Focus ST (2013–2018) has one obvious weak point: the large rear bushing is fluid-filled. Once it starts leaking — dark residue weeping around the mount, handling going vague, a thud over square-edged bumps — that’s the tell. Usually not the arm itself or the ball joint. The bushing goes first.

The arm is stamped steel with an integrated ball joint, which means you can’t press in a replacement joint the way you might on older platforms. The practical fix is replacing the whole assembly.

OEM Replacement Options

For a straight like-for-like swap, Ford OEM arms are available through dealers and online OEM parts suppliers. The part number for the 2013–2018 Focus (non-RS) front lower arm is F1FZ-3078-A. Budget aftermarket brands — Moog and Detroit Axle are the most commonly recommended on the forums — also offer complete assemblies for the Mk3 platform. Moog has the better long-term reputation for durability and isn’t hard to find.

One thing to confirm before ordering: the Focus ST doesn’t always share the same arm as the base hatchback. Verify fitment against the ST spec, not just the model year and body style.

The RS Arm: Does It Fit, and Is It Worth It?

The Focus RS front lower control arm is a different part from the ST item. It produces measurably more negative camber — forum data from owners who have run the swap puts the difference at roughly 0.8 degrees more negative up front. That’s not a rounding error.

For a street car sitting at stock ride height, that’s a meaningful shift. For a car already on lowering springs or coilovers, the extra negative camber can be genuinely useful for cornering grip — or it’ll eat your inside tire edge if you’re already at aggressive numbers. Know your current alignment readings before choosing the RS arm.

The RS arm has also been reported to be less expensive than the ST-specific arm in some catalog listings, which makes the swap look attractive if you need to replace the arm anyway and want extra negative camber without paying for fully adjustable aftermarket components.

Performance Bushing Upgrades: A Different Path

If the arm itself is structurally fine but handling response has gone soft, or you want to dial in camber without swapping the whole arm, bushing upgrades are worth looking at first.

Adjustable Camber Bushings

Powerflex makes urethane front lower control arm bushings for the Mk3 ST and RS that are eccentric-shaped, giving you ±0.5 degrees of front camber adjustment. They run around $155 from Focus specialists and carry a lifetime warranty on the street compound. Urethane is stiffer than the factory rubber, so there’s a real but modest uptick in road noise and feel — most ST owners consider it an improvement, not a drawback.

One install detail: on some Mk3 arms the factory bushing is captured by a rolled-over lip on the bracket. Installing the Powerflex unit can require grinding back that lip before pressing the new bushing in. It sounds more alarming than it is. A small angle grinder and some care is all it takes. Post-install alignment is not optional.

Caster Offset Bushings

SuperPro — available through Steeda and other Focus ST specialists — offers inner rear bushing kits for the ST/RS that add positive caster rather than camber adjustment. More caster means better straight-line stability, reduced torque steer under hard throttle, and sharper steering return. The pay-off is slightly heavier steering feel. Most drivers prefer it. It pairs well with the camber bushing if you want to address both axes.

The CFM and Focus Central Warning Still Applies

The original thread mentions Focus Central and CFM tubular control arms for the Mk1 Focus — and it’s a fair warning to carry forward. Those arms had documented weld failures. The lesson isn’t about those specific companies; it’s about any small-run fabricated suspension component where the catastrophic failure mode is a weld giving way at speed. The Mk3 ST aftermarket is smaller than the old Mk1 scene, and the number of companies offering complete replacement arms specifically engineered for the Mk3 ST is limited. For structural suspension components on a performance car, stick to established brands or OEM.

Alignment Is Not Optional

After any control arm swap or bushing change, a four-wheel alignment is required. It takes very little movement at the arm to throw camber, caster, and toe well outside spec. Out-of-spec alignment will wear tires unevenly and undermine handling faster than whatever was wrong with the old arm. Budget for it upfront, not as an afterthought.

Sources


Similar Posts