HP LaserJet 4 main gear assembly installation instructions
If you notice teeth are missing or worn on the pivot drive gear in your printer (which couples with the fuser gear), you need to replace this part. Missing teeth on this main gear drive will cause the fuser to stop rotating continuously and paper will jam as it enters the fuser.
NOTE: This assembly is only for the LaserJet 4 or 4M; it will not work in the LaserJet 4Plus or 5.
Click here if you need instructions / parts for the LaserJet 4Plus/5 main gear drive assembly instead.