The scene with all the body panels falling off Rosco's patrol car is from the chase at the end of "Mrs. Daisy Duke" (season 4, episode 1). First the front fenders, grille and hood fall off, then the rear fenders, trunk and doors, and finally they lose the roof driving under a low tree branch. Rosco's driving, Cletus is riding shotgun, and Boss, Jesse and Flash are in the back.
Rosco P. Coltrane - master of understatement!