A Visual Experimental Noise Investigation of a Twin Calliper Disc Brake

A twin calliper brake system is investigated using the whole body visual technique of holographic interferometry. It is shown that the disc mode of vibration has a preferred position where a disc antinode is situated under one calliper and a disc node under the second calliper. The maximum angular space occupied by the pad antinode is, as predicted by the theoretical study of the disc/pad interface geometry, the angle subtended by the pad length. For a four-piston opposed calliper the minimum distance is slightly larger than the piston centers. There is evidence that the disc mode position, in relation to the two callipers, may be antinode/node, node/node or antinode/antinode. With these arrangements an accompanying revised theoretical study of the disc/pad interface geometry predicts two stable conditions are possible - if the callipers are positioned either at an angle between 125° to 130° or 165° to 175°. The smaller angle was not tested but the brake became quiet at angles greater than 166°. A brief study of the calliper modes and pad spring retainer is included in the holographic results.