Airbourne Vibrations B737 Classic
LEM, POSSIBLE CAUSES OF YOUR VIBRATION
1) MAIN ENGINE CONTROL / FUEL PUMP this is a known problem with cfm56,a resonating imbalance between 3d cam/speed control weights and the rotating mass of the fuel pump impeller due uneven bearing wear within the main engine control.Can be confirmed by varying thrust and vibs will vary in pitch & strenght.This is usually felt through the flight deck floor. Final resolution is to change the MEC.Boeing/CFM have a service bulletin regarding the matter.This usually appears on a high hour engine.
Regards DDG