Hyundai Repair: 2003 Hyundai Sonata Rear balancing shaft, 2003 hyundai sonata, crank shaft

Question
My car broke a rear balancing shaft belt that broke the crank shaft positioning sensor. I had the sensor, rear balancing belt & timing belt changed. BUT the car is vibrating really badly. Could the belt be off, or could the bearings be going bad on the balancing shaft? Any help would would be wonderful! Thanks!

Answer
It's possible the front balance shaft isn't timed properly.  Without feeling the vibration, it's hard to tell.  It'll be a high frequency vibration, about four times that of a misfire vibration, and it will get worse as engine rpm is increased.

The front balance shaft is particularly tricky to time.  This is because the sprocket for the shaft turns in a 2:3 ratio to the shaft itself.  It's possible that the sprocket pointer can be aligned and the balance shaft is 180 degrees out of phase.  To be sure the front balance shaft is properly aligned with the timing belt off:
1.  Turn the balance shaft sprocket until the marks are aligned.  
2.  Turn the sprocket a small amount in either direction.
3.  If the sprocket tends to continue turning, the shaft is 180 degrees out of phase.  Make one rotation of the sprocket, realigning the marks.
4.  If the sprocket tends to return to align the marks, the shaft is properly timed.  Return the sprocket to its original position.