|Mack Camel Back|
There are lots of trucks and trailers with tandem axles, but alas there are a variety of ways to mount the axles. The classic is probably the Hendrickson suspension which uses a conventionally spring mounted to the frame, and instead of having an axle bolted to the middle of the spring, a bracket is mounted there to hold a walking beam which has axles on each end of it. This was historically common on trucks.
The rubber biscuit suspension is a variant of the classic Hendrickson in that it just eliminates the spring which doesn't flex much anyway and substitutes some rubber pads where the spring would have been. This is often used on trucks.
A different approach is the '4 spring' suspension. You will find this on both trucks and trailers. Each axle is mounted with conventional springs with a small 'flip flop' attached to the inner ends of the springs to allow within strict limits, the axles to equalize the weight. This sort of suspension is very light weight, but not favored for off highway work because it doesn't adjust to uneven terrain well.
Mack has traditionally used a 'camel back' suspension on their trucks. In this design the spring is inverted and used to hold the axle down, instead of the truck up, and the spring is sharply bent over the top of the rocker shaft. It is usually found only on Mack rearends. The spring functions as the walking beam in this configuration.
In another variant of the the inverted spring suspension, a straight spring is used which is below the rocker shaft. Like the Mack Camel back the spring is also the walking beam.
Yet a different suspension is often used on lowboy trailers and log trailers. Shown in the top photo is what we call a Page suspension. Page was a trailer company in Portland at one one. It has no springs at all. The walking beam is fabricated as is most of the suspension. In its basic form it can be nearly all fabricated and the joints flex with some rubber grommets. It is sturdy and reliable.