How to repair a small ceramic and metal air variable capacitor like the ones found in old radio equipment. This applies when the shaft has come loose from the pressed-on hexagonal nut or "knob". In this case the nut which is a screwdriver-adjustment, was cracked and would not hold the shaft against the spring pressure of the bearing, allowing the capacitor's plates to touch and shorting out a tuning circuit. The equipment the cap is in is an old vacuum-tube GE VHF FM transmitter converted to ham radio use. If you can spot it in the picture, you are qualified to do this repair.
Step 1: Remove and examine the capacitor
The removed capacitor is examined. It can be seen that the plates are touching each other. This is bad. I suppose most people would replace the capacitor, but there is no need if it can be repaired.
Somehow the shaft had moved back, forced by the tripod-like spring. The nut on the shaft, which held the shaft in pace, had cracked. This is pointed out because it is important to understahd how the capacitor is held together and figure out why it is broken.