Fix Your Forward Dip In The Jerk

Most important is understanding what should be happening: the trunk should start and remain vertical, which means you can bend only at the knees.
Second, it doesn’t matter if you’re doing a split jerk, a power jerk, a squat jerk, or a push press—nothing about the dip or drive changes. The forward motion of one foot in the split jerk does not mean your whole body moves forward.
Start with a proper stance. Feet between hip- and shoulder-width with the toes turned out—this will be very similar to the snatch and clean pulling stance. Very generally speaking, longer-legged athletes will do better with a wider stance.
Shift your balance slightly more toward the heels, but always keep the full foot in contact with the floor. Exaggerating heel balance, especially lifting the toes immediately prior to the dip, will nearly always cause you to rock forward and actually end up far more forward than you would have been with even whole foot balance.
Pressurize and brace your trunk forcefully with a proper rack position. Any collapse or motion in the trunk will shift your weight forward. This includes not moving the arms or shoulders prematurely in preparation for pushing—the arms and shoulders should be a rock solid, totally motionless platform for the bar until you’re finishing the leg drive.
Make sure the bar is secure in the rack position all the way back in light contact with your throat—the closer it is to your spine, the less it will pull you forward.
Ensure tension in the quads and glutes, and unlock the knees. Note I did not say bend the knees—just move them out of the relaxed, passive lock we normally stand in. This avoids an abrupt, uncontrolled drop before the quads gain control so you don’t lose connection to the bar and get pulled forward.
Move the knees out in line with the feet just like you would in a squat—allowing them to move straight forward is weak and makes forward shifting very likely.
Finally, dip to the proper depth—dipping too deep will move you past a position in which you can reasonably expect your body to maintain control and balance. Use 10% of your height as a starting point and only adjust very slightly from that if needed.
Train and strengthen this optimal dip with the following exercises:
Pause jerk dip squats with a 3-5 second eccentric will allow you to feel and control the motion to ensure perfect balance, position and tension throughout the body. Pause in the bottom for 2-3 seconds, actively maintaining maximal tension, and stand again at a normal tempo. This is the best general dip strengthening exercise.
Pause jerk dips will help more specifically with the ability to brake as quickly as possible in the bottom of the dip, but will also strengthen the bottom position well and help improve your comfort there.
Both of these exercises can be done for sets of 3-5 reps and eventually at weights above your best jerk. However, like with all exercises, avoid the temptation to load them heavier just because it’s possible—if they’re not done correctly, you’re making the problem worse.
Finally, you can use a push press + split jerk, or push press + power jerk + split jerk complex to help reinforce the vertical motion of the body regardless of receiving position. The goal is to make the dip and drive of all 3 exercises identical.