Under extreme braking conditions, some lubricants can’t stand the heat and melt off, evaporate, oxidize or burn. That’s why ordinary, general-purpose chassis grease should never be used for lubricating brake components. It won’t hold up.
What’s needed is a specially formulated, high-temperature brake grease that can withstand the heat, and also not harm rubber seals or plastic bushings.
Petroleum-based lubricants should never be used for brake assembly work because mineral oils can cause seals to swell and fail. What needs to be lubricated? Mechanical components in the brake system that slide, move, rotate or bear pressure.
Why do lubricants work to reduce some brake noises? It is a simple answer. When a caliper finger is lubricated at the point it touches the brake pad, the lubricant creates a boundary layer that separates the vibration of the brake pad from exciting the caliper finger and the caliper.
This is one approach to solving NVH problems that can have its limitations. Lubricants do not dampen forces by adding extra mass like a brake shim. Also, lubricants can not fill in pitting on brake slides. Additionally, lubricants do not insulate against vibration and are only effective for some frequencies.
On disc brakes, lubrication points include the caliper slides and bushings, self-adjuster mechanisms on rear disc brakes with locking calipers, and the parking brake cables and linkage.
There are several basic types of brake lubricants: those that are designed for lubricating hardware and mechanical components and typically contain a high percentage of solids (dry film lubricants), and those that are designed for lubricating seals, boots and other internal parts when assembling calipers, wheel cylinders and master cylinders.
Brake lubricant for hardware is a special high temperature grease designed to provide long-lasting protection. The lubricant may be a synthetic or silicone-based product. Synthetic-based, boundary-type lubricants that come in a tube, paste or stick form have a high solids content and typically contain a variety of friction-reducing ingredients such as molybdenum disulfide (moly or MOS2) and graphite.
Moly and graphite are both dry-film lubricants that can handle high temperatures and pressures. Some of these products are rated to withstand intermittent temperatures as high as 2,400 degrees F!
Moly and graphite have excellent staying power and won’t evaporate or burn off over time, and they won’t attract or hold dirt like ordinary “wet” greases can. This type of product is ideal for high temperature applications where long-lasting metal-to-metal lubrication is essential for good brake performance.
Silicone-based brake grease is designed for caliper and wheel cylinder assembly work because silicone is an excellent lubricant for rubber and plastic. It is compatible with all rubber compounds including nitrile, teflon, nylon and other synthetic rubbers. Silcone’s normal working range is -40 degrees F to 400 degrees F.
But it does not have the high temperature staying power of a high solids synthetic lubricant, and it is a “wet” lubricant that can attract and hold dirt, making it less suited for lubricating external metal-to-metal contact points, such as caliper mounts and shoe pads.
This type of product is best suited for assembling calipers, wheel cylinders and master cylinders.
Another synthetic-based brake lubricant uses polyalphaolefin (PAO) as its main ingredient. PAO-based brake lubricants are also excellent for assembly work and lubricating seals and boots. PAO offers superior rust protection, making it well-suited for brake systems operated in wet environments.
PAO brake lubricant may also include various amounts of moly, graphite and teflon to enhance its lubricating properties.
This type of product can withstand intermittent temperatures of up to 600 degrees F, and can be used for both assembly and external lubrication.
White lithium is a low-temperature grease that can be used to lubricate drum brake hardware and backing plates, but lacks the heat-resistance for front disc brake applications. So this type of grease is not the best choice for general brake work. Regardless of what type of brake lubricant you choose, always follow the supplier’s recommendations as to how their product should be used.
Brake lubricant can also be used to dampen vibrations between disc brake pads and caliper pistons. But it should not be applied between the pads and any noise suppression shims that may be used. Use it on the back of a bare pad or between the pad shim and caliper — and use it sparingly. Don’t glob it on.