This guide will let you know how to crack the SAFE in CRACKED MC Mission in Grand Theft Auto 5 Online: The Criminal Enterprises
You can obtain the crack mission from your MC club bulletin board in the meeting room. After that, you will need to hold the right or left if you on are your PC, A or D, E. You have to hold it until you see the safe dial knob starts to shake.
After that, release it and follow the instruction at the top left of your screen. After that, hold the key again until you see the dial knob starts to shake again, and then release it. It will crack the save, and you can obtain the item inside of it.