The ones I have the entire cap slides out of the pipe flange that's bolted to the cab. You end up with a cap/filter with a 3" smooth pipe nipple sticking out the bottom that slides into the pipe on the mounting flange . It may be tight requiring a little twisting back and forth as you pull up on the cap. If you can get to the mounting screws remove the entire unit from the truck and see how it comes apart, it could be different that the one's I have.
Mike B
