30 Auto Brakes Copyright by Goodheart-Willcox Co., Inc. adjustable screw that passes through the clamp body, Figure 3-6A. A large C-clamp, such as the ones commonly found in hardware stores, is useful for pressing caliper pis- tons into the caliper. Caliper piston compressors, also called brake pad spreaders, are specifi cally designed for the task of pushing caliper pistons back into their bores without dam- aging them, Figure 3-6B. Other clamps can be used to press out rivets, and to remove and install pins at various loca- tions in the brake system. Brake Cylinder Hones Brake cylinder hones are used to remove glaze and deposits from wheel cylinders, master cylinders, and disc brake cali- per bores, Figure 3-7. Th e two general types of hones are the rigid-stone hone and the fl exible hone. Th e rigid-stone hone has two or three spring-loaded fi ngers holding one stone each. Th e stones can be short, for use in caliper bores, or long for use in wheel and master cyl- inders. Th e total diameter of the hone is adjustable within a certain size range. Various hone sizes are available for dif- ferent bore diameters. Th e fl exible hone contains abrasive balls on the ends of fl exible wires. Flexible hones are also available in diff erent sizes. Goodheart-Willcox Publisher Figure 3-6. Tools used to push caliper pistons back into their bores. A—A common C-clamp. B—These tools are referred to as disc brake spreaders or caliper piston compressors. The tool on the upper-right is designed for dual-piston calipers. Note: Not all cylinders can be honed. Some cylinders are coated or anodized and must be replaced instead of repaired. If any cylinder is heavily pitted or cannot be cleaned up by honing, it should be replaced. Both types of hones are operated by a portable drill, either electric or air operated. Th e hone is chucked into the drill, then inserted into the cylinder to be honed. Th e drill is started and hone rotation removes deposits and glazing. A small amount of brake fl uid should be used as a lubricant. Do not exceed recommended hone rpm, if given. Do not allow the hone to leave the bore while it is still spinning as it can fl y apart violently or be damaged. Respiratory Protection As discussed in Chapter 2, brake dust is a constant danger in the shop. You should have a fi lter mask equipped with HEPA fi lters. Do not rely on painters’ paper masks, since they will not protect against the entry of extremely small asbestos particles. Caring for Filter Mask Like any other tool, a fi lter mask must be cared for to be eff ec- tive. Inspect the mask on a regular basis. Check for stretched or damaged head bands, torn or cracked facepiece, torn valve fl aps and damaged fi lter housings. Th e mask should be disassembled and cleaned in a mixture of antibacterial soap and water. Replace the fi lters at every cleaning and any time you notice increased resistance when you inhale. Brake System Measuring Tools Brake system repairs oft en call for making measurements. Th ere are numerous specialty measuring tools. Th ese include micrometers, shoe and drum gauges, dial indica- tors, and pressure checking devices. ekkapon/Shutterstock.com Wheel cylinder Hone Direction of rotation Electric drill Travel limit Ammco Figure 3-7. A rigid-stone brake cylinder hone being used to remove light scoring and deposits from a wheel cylinder.