Broken Spring
This may be a subtle crack in one leaf, or it may be obvious if a leaf is hanging out from the side of the pack. In some cases, a broken leaf may swing out and contact a tire or a fuel tank causing a puncture. Under extreme circumstances, an entire pack may break, leaving you stranded. When looking for a crack look for a dark line perpendicular to the direction of the leaves. A cracked or broken spring will put additional stress on the other leaves and may cause further breakage. With a broken leaf spring, your truck or trailer may lean or sag, and you may notice noise coming from the spring. A truck or trailer with a broken main leaf may wander or experience "dog-tracking."
Shifted Axle
Loose U-bolts may cause the center bolt to break by putting additional stress on it. This allows the axle to shift from front to back and may cause a wandering or dog-tracking.
Fanned Out Leaves
The spring leaves are kept in line by a combination of the center bolt and U-bolts. If the U-bolts are loose, the leaves in the spring can fan out instead of staying lined up in a neat stack. Leaf springs not aligned properly, do not evenly support the load weight across the leaves, causing the spring to weaken, which may cause the vehicle to lean or sag.
Worn Leaf Spring Bushings
Prying on the spring eye should produce little to no movement. The bushings help to isolate the springs from the frame of the vehicle and limit the forward to back movement. When the rubber wears out, the bushings no longer limit the forward to back movement resulting in wandering or dog-tracking. In severe cases, the rubber may be completely worn away, causing loud clunking noises and damaging the spring.
Splayed Out Spring Leaves
This is caused by rust that has worked its way between the spring leaves. Similar to the effect of loose u-bolts, leaves that are not properly aligned will weaken the spring by limiting the contact between the leaves in the stack and not allowing the load to be transferred through the spring effectively. As a result, leaf spring clips may break, and the springs may squeak or make other noises. As is common with any weak leaf spring, the truck or trailer may lean or sag.
Weak/Worn Spring
Springs will fatigue over time. With no other indication of failure, the spring may lose its arch. On an unloaded vehicle, the truck may be sitting on the bump stop or the spring may be laying on the overload spring. With little or no support from the leaf spring suspension, the ride will be rough with little to no suspension movement. The vehicle will sag or lean.
Worn/Broken Spring Shackle
Check the spring shackle at the rear of each spring. The shackles attach the spring to the frame of the truck and may have a bushing. The leaf spring shackles can rust and will sometimes break, and the bushings will wear out. Broken shackles make a lot of noise, and it's possible that they may break through the bed of your truck. A truck with a broken leaf spring shackle will lean heavily to the side with the broken shackle.
Loose U-bolts
U-bolts hold the whole package together. The clamping force of U-bolts hold the spring pack to the axle and keep the leaf spring in place. If U-bolts are rusted and the material is thinning they should be replaced. Loose U-bolts can cause major problems and should be replaced and torqued to spec.