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).