I’m having this problem with my Z axis, I spoke to inventables, and they suggested for me to check if the rod was straight, adjust motor Z axis speed, and dismantle Z axis and try the motor with out the carriage… After all that, it still did the same. Some to them again yesterday and they say I have a bad shield, sent me another one yesterday and I’m getting it today… Does anybody has had this same issue before? Thanks! 
Your video (after 10+ hours?) is still uploading @javierymirna so we have no idea what you are talking about…
Aaahh! No wonder!! 
thanks! I’ll re-upload when I get home!
@javierymirna hi i’ve got somekind of the same issue on mine. for me the probleme was pretty simple to solve. the thread on the delrin ( or teflon ) block was really tight. i had to rethread it ( not too much you don’t want it loose ) and probleme solve ( for me ). hope that help
Try to give the motor a longer startup ramp and reduce the speed. At least that did help in my case.
@Arfst_Braren how do you ‘give the motor a longer startup ramp’?
OK IM ONLY GOING TO TELL YOU THIS ONCE
GO IN TO THE PROGRAM YOU ARE USING
RIGHT CLICK OR GO INTO YOUR SETTINGS AND CHANGE THE Z-AXIS STEPS AGAIN-TILL YOU GIT THE STEPS YOU WANT
If you can turn easily the rod by hand then I’d assume mechanics are ok. Steppers can only turn at low speeds. Make sure you are not asking more than, let’s say 400mm/min (the number after the F in your gcode G0Z or G1Z commands). Finally, make sure the acceleration is also not very high (not sure what hardware you use) try to start with no more than 5mm/s^2 and move up from there. Motor current is also a critical factor, if not enough motor will stall even of speeds are low (not enough torque to rotate the rod).
Hi Guys! Thanks for all your replies! So last night, UPS showed up with a new gshield, which inventables sent me for free, after running some tests they asked me to, they thought it was s bad gshield.
So last night I went ahead and replace the gshield and to my surprise, it kept doing the same thing! 
so I took the whole Z axis apart, and run the motor all by it self with nothing attached, and the motor does the same thing!!at this point I don’t know if it’s a bad motor, or I have bad inputs, I’m reading your comments really careful, and your advice about reducing the speed and steps make sense but I don’t know where to change this settings…
I tried to use UGS but it didn’t work with my Mac, I’m missing a lot of tabs (don’t know why, the latest version will not open at all), so I had to install GRBL, this does work, and I’m able to rotate the motors… I also change the settings from the command line according to what the Shapeoko instructions said… I don’t find a spot in GRBL where I can just change the Z axis speed and steps.
Thanks again!!
Javier
test a file with just these lines with UGS
G1Z10F10
G1Z00F10
Did it move 10mm up and down ok?
Hola Miguel!!
So i need to type that code into the command line?
Thanks!
Using USG you can type both lines as manual commands. But what I meant was for you type these two lines into a text file and use USG to send that file to the ShapeOko.
Ah! Ok, so when I save the text file, whatnots the extension as save it as so USG reads it?
Thanks again!
Exactly, it should move extremely slowly (it should take 1 minute to cover 10mm)
Ok Miguel! I’ll give it a shot and report the results…
Thanks
Ok Miguel, test done… definitely a bad the motor… I entered the commands straight into grbl and it responds but same issue… motor does the same rattling noise but won’t spin… bad news!
Is it possible you have the wires wrong? If we number the four wires in grbl-shield Z-axis connector as 1,2,3 and 4, try replacing 2 and 3.
Let me try that…
It’s also possible that you motor driver power is turned down too low