How much packing?

How do I gauge the proper amount of packing to use on a cartridge style diverter valve?

packing

If you are just adding to the original, then very little extra is needed. If you have removed the entire old packing then you fill the cavity and tighten the nut to compress it.

Ok, thanks! I'll give it a try. The part (american standard) for the shower apparently never came with it. I had installed it for a friend and I may have overtightened it (because there was no packing) and warped the part. It worked fine for some time and then started acting up. So when I get the part again, I will need to wrap the shaft with quite a bit of packing then? The only trouble that I see is if I add too much it will not fully divert to the shower when it is full in.

I'd check with the manufacturer on their web site. They probably have instructions for that specific model. IF not, then a query direct to their help line (probably an 800 number should get it to you). There are some common themes to plumbing, and each manufacturer throws their own curves in. Generic help is just that, get specific help for your part. A pro could tell probably from looking at it. Us DIY'ers need some help once in awhile.

packing

The travel of the diverter stem should be limited by the construction of the valve, not the amount of packing. If the packing is squeezing out and preventing the full amount of travel for the diverter stem, then there is a different problem such as a missing washer to contain the packing.