Every technician has struggled with those little wire clips that push the pads onto the pistons on some calipers. Those little clips that barely fit into the painted-over holes on the new pads and can shoot across the shop like a rubber band can make a big difference.
One racecar builder who specializes in building “showroom stock” vehicles found out just how important this small piece of brake hardware can be. This builder commonly discarded those little wire clips, thinking that they did not provide any advantage in a racing environment.
While between runs on a chassis dyno, he realized that the front brakes of a vehicle needed new pads. Not having time to do the job himself, he had one of his employees perform the job. This time, the tech replaced the missing hardware including the wire clips that pushed the pads against the piston. On the baseline run, the car gained a very small amount of horsepower at the wheels.
The idea of gaining horsepower by replacing the brake hardware seemed impossible. But, after he performed additional runs with and without the clips, he realized that the little clips reduced brake drag. On a street vehicle, it could mean better fuel economy.
SPRINGS AND CLIPS
Heating and cooling cycles can weaken springs and anti-rattle clips. Weak hardware parts can result in excessive caliper/pad movement or binding, causing noise and other related problems. This can lead to uneven and premature pad wear, rotor warpage and pulling.
Some springs and clips can be difficult to install. Some anti-rattle clips may resemble Chinese finger traps when you are trying to reinstall them back on the car. But leaving them out is not an option.
When rust and corrosion build up on a floating caliper’s slides or bushings, it can prevent the caliper from centering itself over the rotor when the brakes are applied. Not only does this reduce effective braking force and increase the vehicle’s stopping distance, it also causes uneven pad wear.
The same condition may also create uneven braking between the right and left calipers, causing the brakes to pull toward the stronger side.
When technicians think of brake hardware, they think springs, clips and slides. But, soft parts like dustshields, grommets and bushings need just as much attention.
Most floating brake calipers use a rubber or plastic insulator or shim around the caliper’s mounting bolts. This sleeve of soft material loses resiliency over its lifetime. This is hastened by the high-temperature environment of the brakes. As materials wear, instead of being round, they are flattened by the torque from the brakes into an oval shape that can cause excessive caliper movement. This can produce noise like rattles and thumps, even if the brakes are not applied.
Unlike steel, soft parts like rubber are sensitive to chemicals. Choosing the right lubricant for these parts is critical to ensuring the integrity of the part.
There are three criteria to remember when selecting a brake lubricant. First, does it say that it’s a brake lubricant on the package? If not, do not use it. Some lubricants may say they are a silicone- or molybdenum disulfide-based product, but they may not be formulated to work on brakes. Second, look at the effective temperature range of the lubricant. At minimum, a lubricant should be able to handle 400° F. Third, check to see if it contains petroleum distillates or any substance that can be detrimental to soft parts.
A shim is a sandwich of materials that is staked to the back of the pad. One drawback to shims is “shim migration” or shifting that can negate its insulating abilities. But, automakers and aftermarket parts suppliers are developing an attachment system to alleviate this problem.
Some automakers stamp notches and posts that index and stake the shim on the pad. Certain manufacturers of shims use pressure-sensitive adhesives to secure the shim to the backing plate. But, over time, moisture and heat can destroy the adhesive. One new design to secure the shim to the pads are clips that clamp onto the sides of the backing plate.
But, remember, a shim does not do its job if it is left in the box.