A visual experimental noise investigation of a twin calliper disc brake

A twin caliper 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 caliper and a disc node under the second caliper. 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 caliper the minimum distance is slightly larger than the piston centers. There is evidence that the disc mode position, in relation to the two calipers, 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 calipers are positioned either at an angle between 125\mD to 130\mD or 165\mD to 175\mD. The smaller angle was not tested but the brake became quiet at angles greater than 166\mD. A brief study of the caliper modes and pad spring retainer is included in the holographic results.