If your vehicle is showing rear end sags when carrying passengers or light cargo, here are the most likely causes and the parts you'll need to fix each one.
Over time and mileage, the steel in coil springs loses its tension and structural memory. This reduces their ability to support weight, causing the rear of the vehicle to sag significantly even under light loads.
Common on trucks, vans, and older SUVs, leaf springs bear the rear load. Constant heavy loads, towing, or simple age causes them to flatten out, lose their arch, or even crack.
While springs primarily hold the vehicle's weight, worn shocks or struts (especially load-leveling or coil-over types) fail to provide necessary resistance. Upgrading to heavy-duty shocks can help compensate for minor sagging.
If your vehicle is equipped with factory air suspension, a leaking air spring, failed compressor, or faulty ride height sensor will prevent the system from automatically leveling the rear when weight is added.
If the rear suspension was recently replaced, standard-duty springs might have been installed instead of the heavy-duty or towing-rated springs required for your specific trim or typical cargo needs.