Lexus IS250: Rear knuckle carrier arm bush wear — alignment wander

The IS-platform rear multi-link suspension uses rubber-bonded bushes at the carrier arm (No. 2 lower arm and toe-control arm) to knuckle attachment points. These bushes are loaded in torsion and compression with every steering, braking, and cornering input and degrade progressively with age and accumulated load cycles. As the bush compliance increases beyond design limits, the rear wheel toe angle is no longer rigidly controlled and shifts under dynamic loads. The resulting rear-end instability manifests as the rear of the car tracking slightly sideways under braking or lane changes, described by drivers as a reluctance to hold a straight line or a vague, unsettled feel at highway speed. Correction requires replacement of the affected trailing or toe-control arms, or professional rebushing, followed by a four-wheel alignment with rear toe adjustment.

• Rear end instability or lateral movement under braking at speed
• Car tracks inconsistently in a straight line on the highway
• Rear wheel toe readings outside specification on alignment printout
• Uneven rear tyre wear, typically on inner tread edges
• Squeaking or knocking from the rear suspension over small road undulations

Visually inspect rear carrier arm bushes for cracking, delamination, or rubber extrusion from the sleeve. Review a current four-wheel alignment printout specifically for rear individual toe readings on each side. Check rear tyre inner edges for uneven or feathered wear indicating persistent toe error. If a workshop inspection is possible: With the vehicle on a hoist, push each rear wheel at the 12 and 6 o'clock positions and then at 9 and 3 o'clock to detect play or deflection at the knuckle mounting bushes.

Parts involved: Ball joint.

$900 to $1,900 at New Zealand independent workshop rates. That is for this job on its own, not for the car.

An estimate, in NZD, for the repair as normally carried out. What a specific car costs depends on which part has failed and what it damaged on the way — treat this as the floor for a negotiation, not a quote.

• “Has the vehicle had a four-wheel alignment recently, and were rear toe values within Lexus specification on both sides?”
• “Have the rear suspension bushes been inspected by a workshop, and was any wear noted?”
• “Does the car feel settled and stable under hard braking or sudden lane changes at highway speed?”

The failure described above is documented in published sources — owner forums, technical service bulletins, recall notices and workshop write-ups — held in our fault database. The inspection instructions and the cost estimate are KickTyres’ own interpretation of them, and it is a starting point for an inspection rather than a manufacturer statement.