Springs

The truck springs are a group of mechanical devices used for ride control. The springs carry the weight of the hopper car body and trucks. They buffer the vertical movement of the trucks and reduce swaying of the hopper car.

Individual truck springs come in a variety of sizes that the AAR has designated D3, D4, D5, D6, D6A and D7 and are packaged together into groups. The number, type and size of the springs used is governed by the weight to be carried and amount of vertical spring travel or compression required. During scheduled maintenance, springs are gauged for their overall free height without load. In the field, they are defective if one or more is missing, broken, cracked, cocked or the wrong type for the hopper car.
Springs can be equipped with inner springs, as shown.

The number and type of springs in each spring group must be the same in all locations. Deviations must be reported to your supervisor. Do not load a hopper car with differences in the spring groups.
This close-up shows the inner and outer springs in this spring group. It is important to look for cracks on the inner springs as well.

It is important to look for cracks on the inner springs as well as for the outer springs. Any inner springs used are locked in by the outer springs. A missing outer spring, obvious on its own, is the only way in which an inner spring can be missing.

The placing of springs is calculated for load distribution. When the load is present, the springs are compressed. You will see a difference in spring height between a loaded and unloaded hopper car. This will affect the height of the hopper car and in turn the height of the couplers. This is why there is a range in allowable coupler heights.
These pictures show some common spring defects
Cracked springs are defects. Aside from load support problems associated with them, broken springs can cause personnel injury if parts of them are ejected during transit.
Do not load or ship a hopper car with a cocked spring.
Spring Seat (Stops)

A missing spring is a defect and the hopper car should not be loaded or shipped in this condition. Spring stops hold each spring in position and a broken stop is one way in which this defect can occur. The missing spring is spotted easily due to the empty area enclosed by the spring seat/stops.

Spring seat designs vary from manufacturer to manufacturer, but function in a similar way-to hold the springs in place.
This disassembled side frame shows the locations where both the inner and outer springs were held in position by the spring stops.

A spring grouping similar to the one from this side frame is shown in the illustration below.
Spring Types (Groups)

Spring groups are combinations of standard coil springs used in each truck side frame. They are selected to match hopper car capacity and vertical travel requirements. The spring group shown here is only one of the possible arrangements.

Stencils on the head of the hopper car heads show the specific spring standard to that particular hopper car.

The nominal new height for the outer spring is 10-1/4" with a test load capacity of 5,500 lbs per spring. The nominal new inner spring height is 10-5/16" with a test load capacity of 2,200 lbs per spring.

When inspecting springs, there are many different arrangements of springs that you might see. It will always be clear if a spring is missing because the spring stops should still be present where the spring was originally placed.
Snubbers (if present)

Snubbers are hydraulic or friction damping devices used in the suspension system of some hopper cars to improve stability. Snubbers are designed to start absorbing energy immediately when the vertical motion exceeds normal ride conditions.

Usually a snubber will replace one spring in the truck spring group. Others are incorporated as part of the truck side frame or bolster design.

One of the major drawbacks of hydraulic snubbers are seal leaks. Leaking oil that has spread 3" from a snubber indicates the it must be replaced or refilled with oil.

Snubbers come in several styles and shapes. When looking at the spring package, a snubber might look like an enclosed spring or like the one shown in this spring group. Depending on the design, snubbers can be located anywhere in the spring group, or restricted to certain locations by their size or shape. This snubber can only replace an outer spring.

Snubbers are not widely used for hopper cars, but are commonly used in gondola cars, especially in those hauling heavy loads of coal.
Only springs that are in the front and part of the second row can be easily seen during an inspection. You can see the rear of each spring grouping when looking through the opposite side frame or from the view below.
Even though you cannot see all of the springs, when one spring goes bad the rest tend to follow. With less spring capacity to support the load, the additional weight is supported only by the remaining springs. A telltale sign may be a bolster which is cocked or leaning to one side under a load.