Nissan Technical Advisor 7/19/2011A vehicle that drops in height over night is a problem. The suspension will not drop unless there is a leak. Like any piece of rubber, the suspension bags have a life span. Most will last several years and well over 100,000 miles. When they do eventually wear out, they must be replaced. This is the key to preventing expensive problems. Most bags fail by developing cracks in the rubber. Air leaks through the cracks and the vehicle starts to drop after sitting. A Lincoln Town Car uses two rear bags. Both can be replaced in under an hour and for a relatively low cost. Not replaced, they will leak, cause the pump to overheat and create a very expensive repair.