Thanks. It's a 1949 Lionel Scout 1110. I'll try to post a picture tomorrow.
The locomotive has a horizontal flat bar, mounted at the very rear, underneath the draw bar.. The drawbar can swing back and forth perpendicularly over this flat bar. But, mounted on the bottom of the draw bar is a flat spring, which runs underneath the drawbar for the length of the drawbar. This flat spring is open, and pushes down on the horizontal flat bar underneath the draw bar. (It rides on the flat bar and crosses over it perpendicularly.) It exerts spring pressure upward, keeping the draw bar from touching the horizontal flat bar.
Unfortunately, the rear axle of the engine, which has one wheel on each side, is also mounted to the underside of the draw bar, further back underneath the engine. As a matter of fact, the axle is held in place by two tabs of sheet metal, that are actually part of the drawbar itself, which are bent downward from the drawbar and have a hole through them for the axel to pass through. As a result, the upward spring pressure on the drawbar also "lifts' the axle and wheels upward as well.
So, the rear axle is kinda "floating" upward, and away from the tracks underneath it. Although the wheels still touch the tracks, there is no downward pressure pushing them down onto the tracks. Accordingly, the wheels often derail easily when they roll over choppy parts of the track, like when the engine goes over a switch. The wheels also frequently derail when the engine is backing up.
It all looks original and untouched to me.