Toilets, Sinks, Showers, Tubs and Disposals - Moen shower valve won't stop leaking despite having replaced stem "cartridge"

About six months ago the moen valve in our shower/tub started to leak. It is the single-handle kind where you pull on, turn right for cold, left for hot. I replaced the stem (or whatever it is called), but about three weeks ago it was leaking quite rapidly again. I replaced it again, but yesterday it started to drip--again.

Might there be something in the housing that might be tearing the rubber seals up? Can anyone offer me advice on how I might fix this problem for good?

Also, I've been told that the handle shouldn't spin around 360 degrees, but should stop at 90 degrees hot and 90 degrees cold. While I have everything apart, how do I fix this?

Thanks in advance for any help.

There should be a cam type stop that prevents movement more than 90 degrees. Your handle will have a pawl on it that should hit this detent and keep the handle from doing this. A new handle may be in order, as those pawls break often. Since you have it down, look inside the brass works with a light and see if there are any cracks in the side walls. If it has been subjected to freezing, sometimes these thin walls have hairline cracks in them. If not, check for rough spots on the walls that may tend to cut the washers/o-rings. you can buff them down with a dremel tool and jeweler's abrasive on a cloth buffing wheel.

He could also have old plumbing, that everytime he turns off the main, rust particles and sand and ? move around and wind up in the mixer. Maybe not right away, but sooner or later.

Get an assistant and flush the valve-body with the cartirdge out. Make yourself something so that water does not get in the open wall cavity, nor shoots clean clear to the back of your shower wall, spraying all over.

Are you on your own well, or city water? Do you have an inline fliter?

And what chandler said about rough spots.