You should see a shaft with a slot in it for a small straight blade screwdriver. Remove the vacuum hose and look into the tube that the hose was connected to. As for the vacuum modulator, they are adjustable. If you're saying that the trans shifts hard with a bit of a clunk or 'jerk' as you described it, when going from park into gear, have you double checked the idle rpm? If it's a bit high, putting it into any gear could create that kick you're talking about.
