Magazine for the auto service professional
Issue link: http://asp.epubxp.com/i/684411
30 | ASP June 2016 Technical Te abutment pads are a throwaway piece and should be replaced any time pad replace- ment takes place. Tese complicated little pieces of metal are designed to provide a fat, smooth area for the pad's backing plate edge to ride on, absorb vibration and provide anti-rattle properties. Some even help push the pads back slightly to reduce drag (more on this in a bit). All of these properties will have been compromised and damaged by rust, heat and fatigue during their life on the bracket, so replacement is paramount. Te next concern involves the guide pins and their boots. Te guide pins locate the caliper to the abutment bracket and must provide free and equal movement for optimum braking and even pad life. But again these components are subject to heat, fatigue, the elements and road debris, so these parts have to be carefully examined and replaced if necessary. Te guide pins must be clean, rust free and straight, but the boots and seals that the pins slide into have to be scrutinized as well. Tey shouldn't be cracked, torn or hardened, as they are designed to allow movement yet provide protection against the elements. In extreme but not rare cases the guide pins can be stuck or frozen in the bracket and replacement may be the only option, but if they are able to be removed, they need to be properly cleaned and new lubricant applied. Te pin holes need to be cleaned of the old lubricant that has gathered dust, moisture and road grime that could impair the pins' free movement. Te boot attachment areas should be clean and rust-free, providing a sealing surface that prevents foreign material from entering the guide pin's hole. In some cases these boots are also a bushing that the guide pin rides on and after many brake applications they deform into an oval or egg shape that can allow rattles by not holding the caliper securely. After cleaning and visual inspections for wear and tear, the guide pins and boots should be reinstalled or replaced and properly lubricated with the correct lubricant. Tis is an area that can't be discounted. Te proper lubricant is critical. Using the old tub of water-attracting white grease simply won't cut it anymore. Te lubricant should be designed to be compatible with the rubbers and seals that it touches, silicone based to prevent water attraction and must be able to properly deal with the high tempera- tures involved. Abutment pad shims should always be part of a complete brake job. The shims wear out and must be replaced and properly lubricated to reduce noise and vibrations. Sliding caliper pins must be clean, free of burrs and corrosion and lubed with high-temperature pin grease for smooth and consistent caliper movement. Never re-use the boots. Worn, pitted and/or gritty sliding caliper pins will cause sliding caliper hang-ups, uneven caliper movement and potential pad drag. Always re- place with new pins, boots and grease.