XJ rear brake calipers are virtually the same from 1969 to mid-1993 but in the mid-Õ70s a larger groove was cut into the pistons to allow for a retaining ring for the rubber dust boots. A correspond-ing groove was cut into the caliper body. In addition, the mount flange was Òfly-cut.Ó Calipers are usually interchangeable as unitsbut the component parts are not. And, in some cases, later cali-pers will not fit an earlier differential, which can be difficult for horodders who donÕt know the history of their rear suspension. Early calipers fit XJ-6 Series I, XJ-6 Series II to 2T.58038, XJ-12 Series I, XJ-12Series II to 2R.54650/2G.50651, 1976 & 1977 XJ-S. Later calipers were used thereafter.