Toilets, Sinks, Showers, Tubs and Disposals - tub/shower diverter knob - delta

I am having a problem with my Delta shower. The shower is activated by a button under the tub faucet. There is one big round knob that you push up for water, then you move it left or right for hot or cold. Under the big on/off knob there is a small push/pull knob that diverts water from tub to shower when pushed and this knob will not stay in to allow a shower, only a bath. It keeps popping out when the water is turned on. I was able to take pliers to it and squeeze it to get it to stay in so we can shower but if I mess with it again the button will pop out and only allow a bath and not a shower. Any ideas on what I need to do? Obviously the least expensive option is what I am looking for, trying to avoid costly plumbing repairs...
Thanks!!!

The diverter is readily available and changeable. I would opt for that, especially since you have boogered the one you have. In addition your water pressure has a lot to do with keeping the diverter engaged. What is your house water pressure? Are you on a well or municipal water?