Grease and Chassis Lubricants

Automotive grease and chassis lubricants are semi-solid or paste-form lubricants that remain in place at lubrication points that cannot be continuously bathed in oil — principally wheel bearings, CV joints, ball joints, steering rack end bearings, brake caliper slide pins, and driveshaft splines. Grease is a base oil (mineral, synthetic, or vegetable) thickened with a metallic soap (lithium, calcium, molybdenum, or aluminium complex) or polymer to produce a semi-solid consistency that clings to surfaces, resists being flung off by centrifugal force, and bridges metal contact surfaces even at rest. The thickener type and base oil together determine the grease’s suitability for a specific application: high-temperature wheel bearing grease must resist liquefying from brake heat; CV joint grease must withstand the high cyclic pressures and sliding contact inside a constant-velocity joint at operating angles; brake caliper lubricant must not attack the rubber boots and seals while surviving temperatures above 300°C. Using an incorrect grease type — particularly petroleum-based grease in contact with rubber components — causes immediate rubber swelling and seal failure. Silicone-based lubricants are used specifically where rubber compatibility is required, such as brake system rubber seals and boots.

Grease provides a boundary lubricant film at contact surfaces that cannot be supplied with oil under pressure. Wheel bearings packed with grease rotate continuously at high speed while supporting the full vehicle corner weight plus dynamic loads from cornering, braking, and road inputs — the grease must maintain a lubricating film across the rolling elements and races throughout the bearing’s service life without replenishment, relying only on the grease reservoir within the bearing cavity. CV joint grease is formulated with molybdenum disulphide (MoS₂) or other extreme-pressure additives that provide solid-film lubrication at the high-pressure contact between the ball bearings and their grooves during joint flexion at full steering lock. Brake caliper slide pin lubricant provides the low-friction surface that allows the caliper to float freely on its pins, ensuring equal pad contact on both rotor faces, while surviving both the heat and chemical environment of the brake system without attacking the rubber boots that seal the pins. Each application requires a purpose-formulated product — substituting general-purpose grease in a CV joint or a caliper slide pin application leads to premature failure of either the joint or the rubber seals.

CV boot failure allowing grease loss and contamination: The rubber boot that encloses the CV joint retains grease and excludes grit. A split boot allows the grease to be flung out by centrifugal force during rotation, simultaneously drawing grit and moisture into the joint. A CV joint that has run without grease for even a short period develops permanent ball groove wear and requires replacement. Inspect boots at every tyre rotation for splits, tears, or missing clamps.

Hardened or washed-out bearing grease: Wheel bearing grease degrades over time from heat cycling, water ingress, and oxidation. Hardened grease no longer flows to replenish the contact zone and effectively becomes an abrasive paste of degraded base oil and metallic particles. This is not detectable without disassembling the bearing. Sealed wheel bearing assemblies replace the serviceable packed bearing on most modern vehicles, eliminating field repacking but requiring bearing replacement on failure.

Petroleum grease on rubber components: Using petroleum-based grease on rubber seals, boots, or hoses causes rapid swelling, hardening, and cracking of the rubber. This is particularly damaging on brake caliper rubber boots and CV joint boots. Always use silicone-based lubricant or the specifically recommended product in contact with rubber.

Level 1 — CV Boot Inspection at Every Tyre Rotation: Visually inspect all accessible CV boot surfaces for splits, cracks, or grease ejection (a black smear of grease on the wheel inner face or surrounding components is the telltale sign of a split boot). A split boot is an urgent repair — the CV joint beneath it is losing lubrication with every rotation. Inspect brake caliper slide pin boots for tears or displacement simultaneously.

Level 2 — Periodic Lubrication at Service Points: Vehicles with grease nipples (Zerk fittings) on ball joints, steering tie rod ends, or driveshaft slip joints require periodic greasing with a grease gun using the manufacturer-specified grease type. Most modern passenger vehicles have sealed joints without grease nipples. Check the owner’s manual for any grease nipple locations and service intervals. Lubricate door hinges, bonnet latch, and boot hinge pivot points with a light machine oil or lithium grease annually to prevent seizure.

Level 3 — Professional CV Boot and Wheel Bearing Service: CV boot replacement requires partially disassembling the axle to remove and regrease the joint or replace the boot as a split design. Always regrease the joint completely with the correct CV joint grease quantity when replacing a boot — do not simply enclose a dry joint in a new boot. Wheel bearing repacking (on vehicles with serviceable bearings) requires bearing removal, cleaning, inspection of roller elements and races, and repacking with the specified bearing grease before reinstallation with correct preload adjustment.