Gear Problems:
Excessive Backlash

Figure 1 - Typical FFT For Ecessive Backlash
Excessive Backlash - Causes high amplitudes at GMF and harmonics. Also, the impacting excites the natural frequency of the gear(s). This can cause unexplained frequencies to appear - they may be the resonant frequencies of the gear(s). The less loaded the gears are, the more effect the excessive backlash has.
Excessive Backlash Symptoms:
  • Higher amplitudes at 1, 2 and/or 3x GMF.
  • High amplitude sidebands around 1, 2 and/or 3x GMF at 1x rpm of one or both of the gears.
  • Amplitude peak at resonant frequency of the gear(s).
  • Sidebands at 1x rpm surrounding the resonant frequency.
Recommended Actions:
  • Inspect gears for proper backlash.
  • Inspect gears for wear patterns and check for proper mesh depth (similar symptoms - see previous page).