In the 1970s and early 1980s when Lionel was part of General Mills, one cost-cutting measure they took was to attach trucks to car bodies with a plastic doohickey. It’s not really a rivet, but more like a clip, and it doesn’t exactly hold the trucks steady.
Removing them isn’t difficult but the method may not be immediately obvious. And sometimes these Lionel cars really did use rivets. I can explain how to remove those as well.
Let’s take care of the plastic gadget first. When you flip the car over, you can see that the underside of the clip is shaped like a V. The trick is to squeeze the two legs of the “V” together, then push them up through the truck. Needle-nose pliers work well for this.
Once you have the trucks removed, I recommend re-attaching them with screws. The screws hold the trucks on with less play, making for smoother operation and fewer derailments.
One of the knocks on Lionel during this era was lower quality compared to the postwar era, and this particular cost-cutting measure was one of the reasons why.
If the truck is riveted onto the car body, you’ll need to remove it with a drill. Find a drill bit that’s about the size of the rivet head. If you have a drill press, the job is easier, but you can use a hand drill if it’s all you have. Flip the car over, then place the drill bit in the opening of the rivet, press downward on the drill, set the drill to spin in the forward direction, and pull the trigger. Work slowly and carefully and keep your hand away from the drill bit so as to not injure yourself. Once you drill away enough of the material around the rivet head, it will pop and the truck will come off easily. Then you can swap trucks or perform any other modification you wanted. When you reattach, I recommend using a nut and bolt like above. It tracks better, and you’re more likely to have a screwdriver on hand than rivets and a press.