Z motors hammering when try to <Z Home>

I am switching from Prusa I2 to Prusa I3 and everything is going well with the transition except that I'm having a strange issue with the Z axis. The (Marlin) values I used with my old Prusa I2 for #define DEFAULT_AXIS_STEPS_PER_UNIT were {80, 80, 3200/1.25, 617} - and the lead screw was M8. Now, with my new Prusa I3, I need to change the the Z value for M5 threaded rod but for unknown reason changing the value from 3200/1.25 to 3200/0.8 when I hit the in Repetier that will make the Z motors to hammer and will not move down. The Z works normal. If I don't change the values in #define DEFAULT_AXIS_STEPS_PER_UNIT and let them as they were for Prusa I2, will work normal. But in that case is not calibrated. The same behavior if I use Cura instead Repetier so I guess might be a Marlin related problem. Anybody got into this problem before? Is driving me crazy...
I would really appreciate if somebody can help me with that.
Thank you in advance

What about the current supplied to the motor? I used Tom Sandlandarer's tips on adjusting the motor current supplied by turning it up slowly, but mine a slight hassle, turn off printer, turn a bit around 1/8 turn then test again, and repeat

It probably about the acceleration too, I remember I get this issue when I put on my other electronic (no stock firmware from supplier and prior knowledge configuring it). And also try to use prusa calculator much easier compared to using '3200/1.25' (no offense on this =))

Also make sure the lead screw can be turned freely all the way from end to end to check if it will be good or not

Another thing might be both ends are not leveled