My shower diverter quit working this morning. (I gave it the tiniest bit of additional torque this morning and now it is diverting only a trickle.) It is the middle knob variety and is probably a Stirling. The diverter assembly hasn't been touched since I bought the house in 1989.

I decided to see what needed replacing. The screw came out just fine, but the knob, which should slide off, won't budge. A friend suggested that corrosion is holding it on and that a few whacks with a hammer will loosen it up. Before I make matters worse, any ideas?

Likely your friend is right. I wouldn't hurt to give it a spritz of penetrating oil or spray lube first. Tapping with one hand while pulling with the other is very effective. Heating with a torch and quenching frees almost anything. It does melt things at times or sets stuff on fire.

You may puchase a knob puller at any plumbing supply house. This tool works on the same principle as a wheel puller. I would not recommend using a torch or heat around a plastic knob but Labmans Idea of spraying it with WD-40 works for me. Merry Xmas, Tom

Thanks guys. It came off with WD-40 and a little hammering.