how to check leaf springs

What we do is jack up the vehicle back end.Place your jack under the frame or bumper centered (if solid and safe to do so) . Not the axle. When you raise the vehicle slowly, do not raise wheels off the ground.Watch to see if the body rises while wheels are left on the ground.If it rises substantially, chances are those springs are shot, whether cracked or not they should be replaced.You will see a noticeable difference in handling and tire wear.

Look at the gap between the top of the tires and the body of the van. If you have to change the springs, you should add new shocks as well. The old shocks will be useless, because they will have been taxed to their limits by compensating for the bad springs.