Uneven braking or judder on overhead and gantry cranes is typically caused by inconsistent friction contact or mechanical looseness. Common causes include misalignment between brake and disc/drum, uneven lining wear, incorrect air gap/clearance, worn pins and bushings creating play, or a brake wheel/disc with runout, scoring, or hot spots. Contaminated linings (oil, grease, moisture) can also create alternating high/low friction zones that feel like vibration or grabbing.
Control timing can contribute as well. If a brake engages while there is still residual speed or torque transition (especially with VFD hoists), the system can jerk and oscillate. The fix is to inspect friction surfaces, confirm alignment and clearances, replace worn joints, and ensure the brake is engaging at the correct point in the motion profile. Use OEM friction materials where possible, because mismatched coefficients can increase judder and instability.