Shower Diverter

I have a three valve shower set up and the diverter is not doing a very good job of diverting. I do get water to the shower head but most still flows through the tub spigot. I pulled it out and looked at it but can't seem to notice anything obvious that could be wrong, but then again I can't tell what brand it is which means I can't locate a diagram. It's brass and uses a turn valve not push type. I think it may be a Delta based on some of the diagrams I have seen on their site. The only thing I can think of doing until I get this figured out is to install a spigot with a diverter to prevent so much water waste. Any help on this would be much appreciated.

Thanks, Tony

Some brands have an additional washser in the diverter stem to backseat when selecting shower. On PP it is a white nylon washer. You may find it missing, and may find some broken pieces of it inside when you remove the stem.

In any event, remove the diverter stem and take it to the store for an exact replacement.