Leaf springs are used in the rear suspension to support the weight of the vehicle and to maintain vehicle ride height . Also, they allow the suspension system to move and adapt to changes in condition of the road. They are commonly found in pickup trucks and some SUV's and minivans. Leaf springs are made up of a series of curved metal strips strapped together. The more strips that are used, the more weight the vehicle can carry.
Leaf springs wear over time and also can become damaged due to the vehicle carrying more weight than it is designed for. When the leaf springs fail then they will need replacing.
Some manufacturers may cover the leaf springs under the bumper-to-bumper warranty section of the factory warranty. There are also some extended auto warranties that will cover the leaf springs as well. To see if the leaf springs of your vehicle are covered, refer to the factory warranty booklet or your extended service contract, if applicable.