Today my brother experienced what a lot of students go through when practicing shorter clubs versus longer clubs, in particular the driver. The biggest point of concern when Adam was practicing during the week was why he was able to hit his short irons well but his longer irons below average. The biggest reason as explained in the video, is that it is true that every swing is the same but when there are some bad habits, they won't show up as much with the shorter clubs.
This is due to them being obviously shorter, with more loft and often having larger sized heads for extra forgiveness. Like a lot of players' swings, Adam tends to be a little steep with his path at times, in particular his downswing. With shorter clubs it doesn't matter too much about being steep however when having longer clubs, the path becomes more pivotal and will require a flatter path so that the angle of attack to the ball is optimal. The steeper the swing, the more you will collide into the ground as well cause an 'outside-in' swing path resulting in 'slices'.
The quickest way for Adam to improve his driving is incorporating a drill that gives him a feeling of being flatter on the downswing. A very common drill I use is the 'T' Ball drill. In 'T' Ball the ball is placed on a big rubber Tee. If you were to take the bat and swing steeply up and down, you would no doubt hit the rubber tee and have the ball drop straight down. This is the same feeling when teeing up a golf ball and hitting too far underneath causing the ball to 'pop' up or 'sky' into the air.
In order to hit a ball correctly in 'T' Ball, you would have to keep the path flat and very much on the same angle going back and through. This is exactly what I had Adam rehearse by holding the club parallel to the ground while gripping the clubhead and making swings back and through keeping the same flat swing path. When using the driver, you should be hitting the tee and not the ground. The flatter Adam keeps his swing path, the more he is able to hit the tee and not collide the driver into the ground.
This drill also has another benefit in that with the path being now flat, he will now develop an 'in-out' path causing draws. With a flatter swing the ball will come off in the right trajectory, with maximum power and accuracy. This is also due to the angle of attack. The steeper the swing, the more backspin is placed on the ball causing the ball to shoot up in the air and then coming down on more of a vertical angle resulting in limited distance. The flatter the path, the less spin is placed on the ball causing greater distance as when the ball falls from the sky it comes down more as a curve rather than straight down.
Once Adam started to incorporate this new path, he was able to hit the ball lower due to the spin rates going down as well straighter with dramatically increased distance. Of course when setting up for a driver ensure also that the ball position is opposite the left heel with 60 % of your weight on the back foot and half the ball being above the Driver when placed on the tee.