Making a swing change? Do it like this.
Step 1: Start by making slow-motion swings with your driver, no ball in front of you. Do this over and over until you feel the change is being integrated with the rest of your swing.
Then hit some balls, with the same slow-motion swing. If you get good shots, move on to step 2.
Step 2: Spend a week swinging your 9-iron with the slow-motion swing. Hit some balls. Hit lots of 9-irons. When you’re satisfied that you can hit a 9-iron with your new swing, move up to the 8-iron.
Keep the pace of your swing slower than normal. Resist the urge to step it up and see how far the ball will go. All you want is clean contact and straight ball flight.
Work your way through the bag one club at a time. If switching to the next club causes your swing to break down, that’s a sign you weren’t really ready to switch. Go back to the one you were swinging before for a few days.
Take your time, there’s no rush. Spending three months on the transition will pay off a lot more than spending three weeks.