There is no spring in that spacer. It is a pin. If your thrust button falls out, do not panic. Stay cool and retreive the button/s with a long magnet. To re-install: get about 3 or 4 feet of straight unbent brake line, and put some straight stiff wire(baling wire) down it. Leave about 6 or 8 inches on your end, and about an 1" or so on the end that'll go down the axle tube. The button has a hole in it, so put the button on the wire and hold it on with a slight kink in the wire. Dab some grease on the button. Snake the button/tube down the axle tube and sink 'er in the hole for the button in the thrust block. Holding the brake tube firm against the block, withdraw the wire and then roll the tube off the button; it'll stay there. Assemble the axle for that side. Repeat the same for the opposite side if the button for that side should fall out. I've done quite a few this way. The 1st time I did it, I couldn't see. To far away for glasses, and to close without them so I looked through a camera with a telephoto. Pain in the arse, but I don't need the camera now.