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Shackle or Slipper: The Layman’s Guide to Trailer Springs

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Trailer springs are an essential part of the suspension but are generally forgettable until something goes wrong. Leaf springs or coil, these trailer accessories are easier to replace when you’re not on the side of a highway with a heavy load, so it’s important to recognise when they’re wearing out.
Springs Explained
Springs come in a wide range, for different conditions and loads:

  • Eye to eye (shackle) springs. The traditional leaf spring, these have both ends coiled in an ‘eye’ into which a bush is placed. The front of the spring is held in a ‘hanger’ while the rear swings on shackle bolts and plates around a rear hanger.
    They’re common in a multi-axle configuration, since the load can be transferred when one axle is carrying more of the weight (such as crossing kerbs) so that it’s more evenly spread.
  • Slipper springs. Simple and long wearing, slipper springs have an eye on one end, while at the other end the open leaves form a ‘tail’ that slides in a hanger welded to the trailer chassis. They’re a low-cost solution to multi-axle trailer suspension as they can be joined sequentially or attached as individual sets, but these do not transfer the load between axles.
  • Parabolic springs. This spring is a slipper type with only one leaf, which is thicker in the middle and tapers at the ends. They work the same as multi-leaf springs, but are ideal for boat trailers because they’re less prone to rust.
  • Tandem Rocker Springs.
    o Eye to Eye springs are most commonly used in this configuration on multi axle trailers. By linking the springs through a rocker assembly, a transfer of load is achieved when one axle is carrying a large percentage of the weight ( like crossing a kerb) so that the loads are more evenly spread.
    o Rocker roller springs, which are a variant on the standard rocker suspension, provide a progressive spring rate and a very comfortable ride
    They’re suitable for horse floats, caravans, livestock and other trailers where the ride is more forgiving than standard suspension systems.

  • Coil springs. Coil springs are becoming a common trailer spring, particularly for of road use, however they require shock absorbers to reduce oscillation over bumpy roads. (leaf springs do this inherently through the friction of the leaves).

When Should They Be Replaced?
Any time you see a crack in the springs, it’s time to replace them. Likewise, if you can see excessive rust build up between the leaves, it usually means they will have reduced flexibility and are at risk of breaking.
Some surface rust is to be expected, but if it is extensive or starts breaking off in chunks, it will compromise the strength and load capacity of the spring.
When the time comes to replace the springs, you will need to know:

  1. The spring type and size appropriate for the trailer.
  2. The totally loaded weight you expect the set of springs to support
  3. The hanger kit that suits the springs.
  4. The U-bolt kit to match the spring and axle configuration.

Check the condition of your trailer springs at least once a year or before taking it out for a run after a long break. They’re reasonably cheap and easy to replace as a whole unit, so don’t be tempted to continue using a worn system.
Need more from your trailer? Here’s how you can enhance its performance by upgrading the suspension.

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