The pull up knob on the Delta diverter spout won't stay up. Water is spitting out of the tub spout during a shower. No water is coming out of the shower head. All these problems are symptoms of a broken or faulty diverter tub spout. This is one of the easiest plumbing problems to fix. There are no replacement parts to struggle with or lose down the drain. You just remove the broken diverter tub spout. Buy an inexpensive replacement diverter tub spout and install it.
Determine if your tub diverter is a set screw or threaded spout by looking for a screw under the spout. Remove the set screw under the spout with an Allen wrench. Slide the diverter spout off the connection pipe. Remove a threaded tub diverter spout by turning it counterclockwise by hand. If the spout won't turn by hand, insert a screwdriver into the end and use the handle as leverage to loosen the spout.
Measure the distance from the shower wall to the end of the connection pipe and write it down. A connection pipe about 6 inches long accommodates the type of diverter tub spout with threads in the nose of the spout. A connection pipe that barely extends beyond the shower wall is for a tub diverter spout that has the threads in the base of the spout.
Insert the new diverter spout onto the connection pipe so it is flush with the shower wall. Tighten the set screw with an Allen wrench.
Wind Teflon or plumbers tape around the threads of the connection pipe and smooth the end down. Screw (clockwise) the threaded tub diverter spout onto the connection pipe until it is hand tight, using care not to cross thread the pipe. If the spout needs a turn past hand tight to be flush and straight, insert a screwdriver into the end for leverage to turn the spout.