Bad wobble during flight V120DO2S

[Birdmanpa]

I recently replaced the tail shaft, large tail gear, the smaller gear is metal as I am using slipper clutch, main gear and front tail drive gear. due to a crash. All servos appear to be functioning properly and have tried a number of freshly charged batteries. What is happening is, once the V120DO2S is airborne and hovering or flying, the tail begins to wobble up and down, it seems to be accompanied by a high pitched chattering that almost seems to be in tune with the wobble. The part about being in tune with the wobble maybe my imagination as I am now looking for anything. I have tried adjusting the rx. rudder pot from 11:00 to about 2:00, which is where it seems to fly best and where it was prior to crash. The first pot is at about 12:00 and the ext is about 11:00, these have not changed. I am flying with a WK2801 Pro. I have tried adjusting the gyro which is in Gyro/AUX2 from 65% to 75%. It appears to run best at 75%, but still has wobble in full range. It does it both in normal and throttle up positions. Rudder D/R is 100% EXP lin. I am not sure what to look for. Neither the motor or servos are heating up at all.
Any suggestions from you folks would be greatly appreciated.
Incidentally none of the none of the gears I replaced seemed to be damaged badly in the crash, but when I picked up the heli after, I saw that the rear lge gear attached to the shaft had come off which is I believe what caused the crash to begin with as I lost complete control and flew into a wall. Just an aside.

[jamichx]

have you tried to replace the feathering shaft ? also have you examined tail boom it could be cracked. to do that you have to remove it to see as it normally crack right where the servo is attached. first I would check the feathering shaft.