GMwrencher Those rear cab mounts intruduce rubber into the mount system because you know when the frame flexes something has to give. Those old time rivited frame guys really put the frame thru it's paces,and afterwords frame still strajght rivets tight ready for more !! My 51 6400 out there has hauled thousands of bushels still just fine,had a few chain bites from poor hitching,nothing a BFH wouldn't take care of !!