The pawls (small spring activated plates) inside the freewheel body are stuck down and cannot spring back up to engage the gear body.
This is usually caused by oxidation and moisture.
This is a long term issue, the freewheel really should be replaced. It may randomly work if you can get a lubricant to penetrate into body, but this is normally a short term solution.
Most freewheels from Sram or Sunrace will run about $20.00.
Answers & Comments
The pawls (small spring activated plates) inside the freewheel body are stuck down and cannot spring back up to engage the gear body.
This is usually caused by oxidation and moisture.
This is a long term issue, the freewheel really should be replaced. It may randomly work if you can get a lubricant to penetrate into body, but this is normally a short term solution.
Most freewheels from Sram or Sunrace will run about $20.00.