When a car’s springs sag over time, other parts get worn down too.
Installing new springs with old hardware may cause vibrations in these parts. This is why it’s important to use fresh attaching parts when installing new springs.
After replacing old springs, it is not uncommon for vibrations to appear.
Unless you specify otherwise, new springs will put your vehicle back to the stock factory ride height, but the following also applies when setting the vehicle at any ride height prior to replacing the springs.
All those other suspension and steering and driveline parts have worn themselves to the old sagging ride height.
Resetting the ride height can bring out the need to replace some of those old parts.
Replacing the old spring bushings, isolators, shackles, and u-bolts can eliminate one area of concern when dealing with vibrations after a spring install.