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SAE J2521 noise tests are conducted to examine the impact of shim and grease on brake squeal generation. The impact of adhesive (bonded) shim, clip-on shim and grease for noise generation are examined. Low frequency squeal is eliminated by the application of grease on both adhesive (bonded) shims and clip-on shims. The role of shim and grease for reducing brake squeal is discussed. Adhesive (bonded) shims were found to be effective for high frequency squeal (pad bending mode) by increasing damping. Grease is effective for low frequency squeal (pad rigid mode). The mechanism to eliminate low frequency squeal by the application of grease is investigated. Friction between the shim and caliper piston/finger is reduced. Pads contact directly to the anchor bracket. As a result the contact stiffness is increased. The mechanism is confirmed by experiments.

In the past, in order to have good brake effectiveness, it was necessary to adopt high coefficient friction materials for pads or linings, or enlarged brake effective radii. But high coefficient material can create problems such as noise or vibration. And increasing effective radii is limited by the wheel package. A high pedal ratio can provide good effectiveness, but also leads to long pedal travel and poor brake feel. Specifically for trucks and SUV's with large GVW's, it can be difficult to achieve both good brake effectiveness and good pedal feel. In response to this difficult design challenge, a double link-type variable ratio pedal was developed for a production application.