Replacing a faulty 20 year old American Standard shower valve that had low pressure and flow with an intermittent knocking sound from hot water line. After removing the cartridge I found the problem was copper wire shavings (from upstream plumbing) was partially clogging the hot water inlet of the pressure balance unit inside. It might have been salvageable with a good cleaning alone.

The two main replacement parts used in this video are as follows:
1. Outside white piece which attaches to shower handle is American Standard Cartridge, Plastic/Ceramic (Model #0235290070A).
2. Inside gray colored piece American Standard Pressure Balancing Unit for SingleControl Tub/Shower Valve (Model #M9521000070A).

On further study, I looks like my existing outer cartridge was American Standard47 MM BacktoBack Cartridge, Model# 9523770070A. According to the American Standard website the only difference between the two is "the back to back cartridge is used when the hot and cold lines have been reversed. The 0235290070A is the standard cartridge."