When two objects move relative to one another, the molecular interaction between the two surfaces leads to wear. Wear occurs by several mechanisms, which material scientists categorise as adhesive, abrasive, fretting and erosion. All of these can be avoided by keeping the surfaces separated by a film of lubricant.
In a brake caliper, the pads move in their abutment slides not only when the brakes are applied, but when vibrations are transmitted from the road surface and drivetrain. Whenever there is motion at the brake caliper, there is relative movement between the sliding components.
Some of the mechanisms of wear are closely related to corrosion, where oxygen from the air reacts with metal to form oxides. These oxidisation products are much harder than metal, and when present at a sliding interface can act as an abrasive, rapidly accelerating the mechanical wear rate. A key to avoiding this accelerated wear process is to avoid the formation of metal oxides, by excluding oxygen-rich air from the surfaces – best achieved by coating the surfaces with lubricant.
In its early stages, wear on the abutments of the caliper is microscopic, creating a roughness on the slides. But the damage is cumulative, and will get worse over time. Although the brake may function properly at its first pad change, over the course of years the wear on the slides will increase until the pads are no longer able to move freely. Pads jamming in the caliper can lead to many brake problems, including shudder, drag, rapid pad wear and overheating. It is good workshop practice to delay the onset of this wear damage, or eliminate it altogether, by providing appropriate lubrication at the contact points.
The noise behaviour of a brake system is a complex interaction between all parts of the brake; the pads, caliper, rotor, and often the suspension components. When several components go into resonant vibration together, a positive feedback system can form, leading to brake noise.
One strategy for avoiding brake noise is to isolate the pads from the caliper. Decoupling the caliper from the pads adjusts the dynamics of the brake system, changing the noise properties.
Applying lubricant between the backplate of the pad and the piston and fingers of the caliper is an effective way to isolate the pads and decouple a system resonance.
Many Japanese OEM pad manufacturers use multi-layer clipon shims with a layer of grease between them to achieve this isolation effect. If the OE shims are to be reused on an aftermarket brake job, then the grease should be replenished with a suitable brake lubricant.
The guide pins of a sliding caliper require lubrication to operate properly, allowing the caliper to centre over the rotor, and adjust to accommodate pad wear. If the pins are not lubricated, pads may drag on the rotor leading to overheating, rapid wear or shudder. Whenever the pads are replaced, each caliper should be inspected and tested, and all sliding components lubricated.
Having established that lubrication is a good idea when replacing brake pads, it becomes a matter of choosing the best product for the job. The brakes of a car work under uniquely demanding conditions, which require a specially formulated lubricant. Any grease will do the job temporarily - even water can be an effective lubricant until it dries. Designed specifically for brake systems, Bendix Ceramasil Brake Parts Lubricant will last the life of the brake job.
Brakes need to operate effectively at a range of temperatures, from the coldest winter mornings to the scorching heat generated by hard-working brakes on a mountain descent – temperatures that will melt a conventional grease. Exposed to the worst undercar conditions, continuous jets of road water in downpours and clouds of dust on dirt roads, it’s a product that has been created specifically to protect and lubricate brake systems under extreme duty conditions.
New Caliper
Brand new caliper with OE grease on the slide pin. This should be replenished when the pads are replaced to ensure the caliper can slide freely for the life of the brake job.
Caliper
Apply lubricant to the abutment slides of the caliper, so the pad can slide freely without jamming or causing wear.
Lubricant Application
Apply lubricant between the back plate and the caliper fingers to isolate the pad and break resonant coupling between the pad and caliper.
Caliper Bolt
Caliper bolt should be lubed when re-assembled.
Used Caliper
Clean off the gunk with a wire brush and apply lube to the abutment shims before re-assembly.
Japanese OE Pad
Japanese OE pad with multi-layer shim. Replenish the grease between the shim layers if they are to be re-used.
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