The two most likely clunks from the rear of the car are driveline lash and UCAs. This fix addresses the UCAs. If you installed a urethane bushed UCA from the aftermarket and used the factory front UCA bracket, you're guaranteed a clunk. All the UCAs, factory and aftermarket, use a 14mm bolt in the front. Ford, in their infinite wisdom, put a 16mm hole in their bracket. There are two fixes. The best is to use the fabricated bracket from your UCA vendor. Second, Steeda (555-4110 - $9.45 at Summit) and UMI (1058 - $7.99 from UMI) make a stepped spacer that reduces the factory hole to 14mm. Needless to mention, proper torque (129 lb/ft) is also a must.
Edited by 54First, 24 June 2012 - 10:11 AM.