My dad sent me these for the '11's but I've found it applicable to my son's '07 as well so these codes are probably pretty consistent through the years. F-150 axle codes Vehicle Rear Axle Ratio Non-limited Slip Rear Axle Code Limited-slip Rear Axle Code F-150 3.15 15 A5 3.31 27 Not Available 3.55 19 H9 3.73 26 B6 3.73E N/A L6 4.10E N/A L4 Found either on the door or pillar post.