28 and tapers through the middle portion 32 to a relatively thin layer at the second end 30 the variation in the thickness of the liner 26 results in the variations in density a second embodiment of the assembly 10 is shown in fig3 the second embodiment includes all of the elements described above for the first embodiment in the second embodiment the friction material liner 26 has a greater density at the second end 30 than at the first end 28 as shown in fig3 the liner 26 is relatively thick at the second end 30 and tapers through the middle portion 32 to a relatively thin layer at the first end 28 referring to fig4 a third embodiment of the assembly 10 is shown the third embodiment includes all of the elements described for the first embodiment in the third embodiment the friction material liner 26 has a greater density at the middle portion 32 than at the first and second ends 28 and 30 as shown in fig4 the variations in density are the result of the relative thickness of the liner 26 at the middle portion 32 as compared to the thickness of the liner 26 at the first and second ends 28 and 30 it has been found that for each of the above described embodiments the thickness of the liner 26 can be varied in the range from about 0 020 inch to about 0 050 inch with the range of about 0 032 inch to about 0 042 inch being preferred the above detailed description of the present invention is given for explanatory purposes it will be apparent to those skilled in the art that numerous changes.