One of the main areas affected by a lift is the angle of your drive line. That angle at which the drive line goes into the T-case must be correct or you can get a growl or drive line vibration. These transfer case drop kits are designed to lower the transfer case to correct the drive line angle of a lifted truck. If you purchased your suspension package through Jack-it and a transfer case drop is necessary, it will be included (except the Jeep XJ kits).