Sounds like a "torsion axle"?
Any visible leaf springs?
If no leaf springs and the axles are directly mounted to the frame then you would have what is called "torsion axles" which in a nutshell are like a heavyduty rubber band inside of the axle tube..
Looks like this..
Torsion axles have been around for a long time are are pretty reliable, some folks prefer them over leaf springs for a smoother ride..
You can read up on torsion axles
HERE at Dexter Axle website.
Otherwise if there are leaf springs there should be a leaf spring for each axle and a mount and equalizing link between the springs..