Your tandem, or double axle, trailer is built to haul heavy loads. Leaf springs are installed to absorb the shock of repeated up-and-down motion, protecting the axles from the force of impact. The axles are suspended from these springs, which are connected to centre equaliser bars. The equaliser bar distributes road impact across both sets of axles and leaf springs, minimising disproportionate weight on a single axle.
Place blocks or jack stands under the four corners of the frame, and raise the trailer off the ground.
Install the equaliser bars to the middle hangers on either side of the trailer. Fasten the centre holes to the hangers using spring bolts.
Attach the four leaf springs to the centre equaliser bars on either side of the trailer, using spring bolts.
Set the front axle across the centres of the front leaf springs. Raise one front leaf spring at a time, attaching the free end to the front hanger using a spring bolt. The front axle should be suspended across the front leaf spring pair.
Fasten the front axle to the front leaf springs. Attach a U-bolt and retainer bracket to either side of the axle, at the point of contact with the leaf springs.
Set the rear axle across the centres of the rear leaf springs. Raise one rear leaf spring at a time, securing the free end to a rear hanger using a spring bolt. The rear axle should be suspended by the two rear leaf springs.
Secure the rear axle to the centre of the rear leaf springs, attaching a U-bolt and retainer bracket on either side of the axle.
Tighten all the bolts to the manufacturer's torque specifications, using a torque wrench. Remove the blocks or jack stands, and lower the trailer.
Make sure to align the axles, according to the manufacturer's specifications.