Magazine for the auto service professional
Issue link: http://asp.epubxp.com/i/684411
32 | ASP June 2016 Technical Many brake lubricants now even contain PTFE (Tefon) to improve the lubricant's performance. Anti-seize should not be used on the guide pins or boots; it is not a lubricant and will ball up, gather dust and cause a whole host of issues. The brake rotor In most cases a new rotor is going to be installed, but if we just machined it, either on the vehicle or a lathe, it is important to wash the rotor clean with mild soap and hot water to remove all the metal debris and graphite from the previous brake pads and machining process. Yes, I said soap and water, the use of a brake cleaning solvent isn't sufcient to properly remove all these leftover materials, as it evaporates too fast. It's this leftover material that can ruin even the most thorough brake service. When not properly removed from the surface of the freshly machined rotor, materi- als left over from machining (too small to be visible to the eye) can be transferred to the new pads, and this can result in noise, uneven braking and a host of other issues. Many times the problem is fxed by chang- ing the pads that are contaminated with the small machining particles, with a new set of non-contaminated pads. But the actual issue was improper cleaning of the machined rotor. Rotor run-out should also be checked. Just a few thousandths of an inch over the spec can cause uneven pad transfer to the rotor that results in uneven braking and vibrations, usually within the frst 3,000 miles of driving. Te softer pad materials that were used for years (late 1970s, '80s and '90s) were quite forgiving and didn't as a rule generate much noise or cause excessive rotor wear. Te problem was that they often contained asbes- tos, so the brake pad manufacturers changed to a semi-metallic or a ceramic compound that can cause noises and wear rotors, but these compounds require a very true rotor. Ceramic pads are the worst for this, as a small amount of run-out will unevenly deposit transfer materials across the surface of the rotor, and this creates a slap-stick action that mimics a bad rotor. Use the lug nuts to tighten the rotor to the clean, rust-free hub surface, and check the run-out with a dial indicator. If it's over 0.002- inch you have a problem (the old spec was no more than 0.007-inch). Just try indexing the rotor a couple of times, and in most cases the problem is solved. Shims are available and Above are examples of new brake pads with new vibration shims and pad separators. With the brake caliper removed, it becomes obvi- ous that the abutment bracket surfaces on the caliper bracket are corroded along with dam- aged pads, shims and stuck slider pins.