Hello, I just did a cosmetic makover to my bathtub. I replaced the handles, tub spout and the shower head. I had a leak on the cold side so I replaced the stems also, the HOT, COLD and DIVERTER. I took the old stems to the store with me to make sure I got the correct ones (I did not know brand of faucet). The cold and hot stems went in and work perfectly but the diverter though it went in fine I have water coming out both the spout and the shower at the same time. It seems like no matter what I do I can not slow the water coming out of the spout while turned in the shower position. These are brand new stems so I know they are not bad (or shouldn't be). The brand of faucet is "Sayco", I only know this because of the matching up of the stems.

The valve it's self may need to be serviced. The stem may work but the valve that switches from spout to shower head may need to be replced.

The stem is the valve so the last post confused me. Is you new stem 100% exactly the same as the old stem? Make sure the stem is unscrewed before you try to install it, if not it will never seal completely. Or, you could try just replacing the washer and seat on the old stem. Last but not least look inside the valve body to see if there are any nicks on the old seat, rub with your finger tip. If its nickd it must be resurfaced