Leaf Springs

Leaf springs are long, arc-shaped spring steel strips (or packs of multiple strips) used as primary suspension springs on rear axles of trucks, SUVs, and older passenger vehicles. A typical leaf spring pack consists of a main leaf (the longest, with eyes at each end for mounting to the chassis) and several progressively shorter leaves stacked above it, held together by a centre bolt and spring clips at intervals. The spring eye mountings allow the spring to arc (change radius) as it deflects, with one end using a fixed shackle and the other a swinging shackle to accommodate the length change. Leaf springs are extremely durable, provide both spring rate and axle location functions simultaneously, and are well-suited to high load applications. Their main disadvantage is weight and a harsher ride compared to coil springs.

When a load is applied to the axle (road bump, heavy payload, braking torque), the leaf spring flexes, increasing its arc radius and absorbing the energy as elastic strain in the steel. The number of leaves and their thickness and length determine the spring rate and load capacity. Single leaf (mono-leaf) parabolic springs are used on many modern trucks for their lighter weight; multi-leaf packs are used where high load capacity and durability are required. The spring also locates the axle longitudinally — preventing the axle from moving forward or backward under braking and acceleration torque. This dual function (spring and suspension link) is why leaf springs do not require separate trailing arms or Panhard rods in many truck designs. The U-bolts that clamp the axle to the spring centre must be torqued correctly to prevent the axle from rotating on the spring under braking loads.

Broken leaves: Individual leaves fracture from fatigue, typically at the point of maximum stress near the centre bolt or at corrosion pits. A broken main leaf causes the spring to sag and lose alignment. Broken secondary leaves cause load capacity reduction and rattling. A broken spring eye is dangerous and requires immediate replacement.

Worn or deteriorated silencer pads and inter-leaf inserts: The plastic inserts between leaves prevent metal-to-metal contact and squeaking. When worn, the leaves contact directly, causing metallic squeaking during suspension movement — particularly when loading and unloading the vehicle.

Worn or seized shackle bushings: The rubber or bronze bushings in the spring eye and shackle wear or seize, preventing the spring from changing length freely during deflection. A seized shackle bushing binds the spring movement, causing a harsh ride and stress risers that crack the spring.

Level 1 — Payload and Sag Monitoring: Inspect rear ride height quarterly — sagging below the normal laden height at rated payload indicates fatigued or broken spring leaves. Listen for metallic squeaking from the rear suspension during loading transitions — worn inter-leaf inserts or shackle bushings are the primary cause.

Level 2 — Lubrication and Bushing Inspection: Grease the spring shackle pivot pins at every service interval if grease fittings are provided. Inspect rubber spring eye bushings for cracking or extrusion at the eye bore. Check U-bolt torque annually — loose U-bolts allow axle rotation causing handling instability.

Level 3 — Leaf Pack Replacement: Replace the complete spring pack when a main leaf breaks — do not attempt to replace individual leaves in a worn pack, as the remaining leaves are at similar fatigue levels. Replace as an axle pair to maintain balanced ride height and handling. Torque all U-bolts to specification after installation with the vehicle at normal laden height.