Leaf Spring Kits

A leaf spring kit supplies the springs along with the hardware needed to fit them, rather than leaving you to source the rest separately.

That matters more on leaf springs than on most suspension components, because several of the fasteners involved are single use and cannot go back in.

What a Leaf Spring Kit Includes

Contents vary by application, though most kits are built around the same idea.

A vehicle kit supplies the spring pack for one axle, usually as a pair, with the U-bolts, centre bolts, nuts and spring eye bushes required to fit them.

Some kits extend further, adding shackles, shackle bolts, hangers or pins depending on what the application needs and what typically wears out alongside the springs.

Trailer kits are often more complete again, since a trailer suspension is a simpler assembly. A single axle kit can include the springs, front hangers, shackles, dumb jacks, shackle bolts, nylon bushes and the U-bolts to clamp it all to the axle.

Check the listing for what is actually included rather than assuming, since the same product name covers quite different contents between suppliers.

Why the Hardware Should Go In With New Springs

This is the practical argument for buying a kit rather than springs alone.

U-bolts are torqued into their yield range and stretch permanently as a result. Once undone they should not be reused, and fitting new springs with old U-bolts is the most common corner cut on this job.

Centre bolts have been clamped under high load for the life of the pack and have usually corroded. They cost very little and they are what locates the pack on the axle seat, so reusing one is not a sensible saving.

Spring eye bushes wear on the same timeline as the springs, and the access to change them is already being paid for when the pack is off.

Shackle bushes and pins follow the same logic. A new spring pivoting on worn shackle bushes will not behave as intended and the noise will be blamed on the springs.

Buying these together also avoids the job stopping halfway while something is ordered.

Vehicle Leaf Spring Kits and Load Ratings

Australian vehicle leaf spring kits are specified by constant load rather than by lift height alone.

A kit rated at 300kg is designed to sit at its nominated height while carrying 300kg permanently in the tray or on the chassis. Ratings run from around 50kg up to 800kg across the range, with lift heights typically between 20mm and 80mm.

That rating refers to the weight you are adding rather than the weight of the vehicle. A tray, a canopy, drawers, a water tank and tools add up quickly, and people consistently estimate low.

Front and rear kits are specified separately on vehicles with leaf springs at both ends, since the two carry entirely different loads.

Choose the rating around what the vehicle actually carries day to day, not around its maximum capacity or how it sits empty.

Trailer Leaf Spring Kits: Slipper, Shackle and Rocker Roller

Trailer kits come in arrangements that are not interchangeable, and matching the kit to what is already on the trailer is the first thing to establish.

Slipper spring kits use an eye at the front and a flat open end at the rear that slides in a hanger. They are simple and common on single axle box trailers.

Shackle spring kits use eye and eye springs with a swinging shackle at the rear, giving more controlled movement and suiting heavier loads and multi-axle setups.

Rocker roller kits link the springs of a tandem axle through a rocker, so load transfers between the two axles over uneven ground. That keeps both axles loaded crossing gutters and rough tracks.

Slipper and shackle arrangements use different mounting hardware entirely, so a kit for one will not fit a trailer set up for the other without changing the hangers.

Single Axle and Tandem Axle Trailer Kits

Kits are sold by axle configuration as well as by load rating.

A single axle kit covers one axle with a pair of springs and the hardware for both sides.

A tandem kit covers two axles and includes the additional hangers and the linking hardware required, which on a rocker roller setup is a substantially different arrangement to two single axle kits bolted on separately.

Load ratings are given per axle, so a tandem trailer rated at 2000kg is typically running two 1000kg axles rather than one assembly rated at the total.

Check the rating against the trailer's ATM rather than against what you usually carry, since the suspension has to suit what the trailer is legally rated to.

Requirements around trailer suspension vary, and it is worth checking the manufacturer specification and the current rules for your state before changing components.

Galvanised Leaf Spring Kits and Corrosion Protection

Finish matters more on trailer kits than on vehicle ones, and it is worth paying attention to.

Galvanised and zinc coated hardware resists the corrosion that finishes trailer suspension components, and on a boat trailer it is the difference between a kit lasting years and lasting a season.

A boat trailer is submerged on every launch and retrieve, so the springs, the U-bolts, the shackle bolts and the hangers all see salt water directly. Corrosion resistance on that application is more important than load rating by a wide margin.

Vehicle leaf springs are generally painted or coated rather than galvanised, since they are not submerged, though coastal and agricultural vehicles benefit from better protection than the standard finish provides.

Helper Kits and Add a Leaf Kits

Not every kit replaces the spring pack, and the alternatives suit different situations.

A leaf spring helper kit works alongside the existing pack, adding support only when load goes on. Airbag helper kits do the same job using air rather than steel, with the advantage of being adjustable.

An add a leaf kit inserts an additional leaf into the existing pack, raising the vehicle slightly and adding some capacity. It is the cheapest route to more support and the trade-off is a firmer ride, since you have added spring without redesigning the pack around it.

A leaf spring lift kit replaces the pack entirely and gives you the capacity, the ride height and the travel designed together, which is the proper answer on a vehicle that is permanently loaded.

Helper kits suit a vehicle that is empty most of the time and loaded occasionally. A replacement kit suits one that carries weight continuously.

Matching a Kit to What You Already Have

A few checks before ordering save a return.

Measure the existing springs, specifically the eye to eye length, the width of the leaves and the eye diameter. Those three figures determine whether a kit will physically fit.

Count the leaves in the current pack, since that affects the centre bolt length supplied in the kit.

Check the spring width against the hanger and the axle seat, since 45mm and 60mm are both common on trailers and the hardware differs.

On a vehicle, confirm whether the kit is for the front or the rear and whether it suits your body style, since a cab chassis and a dual cab on the same platform frequently use different rear springs.

Check what the kit includes against what you are replacing, so you know whether a shackle kit, hanger kit or bush kit is coming with it or needs ordering separately. Leaf spring to coil conversion kits are a different product again and change the rear end entirely rather than renewing it.

Torquing a Leaf Spring Kit and Why It Needs Retorquing

Leaf spring work involves heavy components with the vehicle or trailer supported, and a pack under its own arc will move once the fasteners come off.

Fit the new U-bolts rather than the old ones, and torque them evenly and in sequence rather than one at a time.

Make sure the centre bolt head seats fully into the locating hole in the axle seat before the U-bolts are tightened, since that head is what holds the pack in position on the axle.

Retorque the U-bolts after the first few hundred kilometres. A new pack settles as it beds in, the U-bolts relax, and that first retorque is not optional.

Check the shackle angle on anything where the ride height has changed, since a lift alters where the shackle sits and how the suspension travels.

Fulcrum has been working on suspension since 1976, across 16 Service Centres and 200+ authorised workshops nationwide, and leaf spring work is a core part of what the network does.

Find Leaf Spring Kits for Your Vehicle

Select your vehicle to see the leaf spring kits available for it, in standard, heavy duty and raised specifications. Check the constant load rating and what hardware is included before ordering. Warranty and a fitment guarantee come with everything we sell, supported by workshops in every state.