Larger pads hold more liquid weight, this is why there is a heavier counterweight, to help compensate weight disribution. As pads, weights and backing plates reduce, so should the counterweight. I quote, from Coastaltool.com: "The counterweight is a half-moon shaped piece of metal attached to the rotating shaft of the tool. This smooths out the random orbit action by providing a counter balance to the elliptical orbit of the rotating backing pad. If you change the pad size you must also change the counterweight or suffer unnecessary vibration and possible damage to the tool.
There are two different counter-weights which are clearly marked to indicate use with either the 5" or 6" backing pad. Therefore if you decide to outfit the 7335 5" Sander with a 6" backing pad for sanding or polishing you must switch to the counterweight used with 6" backing pads. The same goes for the 7336 6" Sander. If you decide to outfit it for 5" sanding or polishing you must switch to the counterweight used with 5" backing pads.
I choose to follow this advice, as well as recommended it. Im not here to argue with those who do it different, I have just had success, and figured if it works this way, why dismiss the feasibility of it.