How do you change the cartridge in a Cuthbert shower diverter valve?

Answer 1

Note: this is for a Cuthbert brand shower diverter installed in 1977. It's a separate valve between the hot and cold, and above the tub spout but below the shower head.

I just did one of these and it's a very clever but tricky design. I wasted hours before I figured out how simple it is. First, remove the knob by taking out the screw in the centre. Then, remove the brass nut - I found a 13/16" automotive spark plug deep socket fit perfectly. Just turn it counter-clockwise and the fine threads come undone, and the nut comes off, leaving the packing in the hole around the stem. Here's the trick bit - put the handle knob back on and turn it counter-clockwise. This pushes the stem backwards into the outer cartridge. Since the stem is against the back seat, it can't move back, so the outer cartridge comes forward and out. Once it's loose and part way out, then pull out the cartridge by pulling on the centre stem with pliers. Out comes the whole works. Clean out the inside of the pipe, and put in the new cartridge. In my case, I found that after I put the new cartridge in, I couldn't quite get the nut to start threading, so I cheated by taking a razor blade to the packing and slicing about 1 mm off of the thickness. That got the nut far enough back to engage the threads. It seems to work well now.