It is fairly common on the HP LaserJet 5000 & 5100 series printers to see 2 fuser drive gears wear out. If you hear a grinding noise, popping noise, and/or jamming near the fuser entrance you may need to change these gears. The 2 gears in question are part of the main drive assembly; the gears include a swing arm gear which turns the fuser, and the 29-tooth/14-tooth double gear which drives it. This kit includes both gears and it is recommended you change both. Replacing these gears is considered a medium-to-advanced level repair; as you will have to remove the outer covers and remove and disassemble the main gear drive assembly.