Can anyone ID this old Amer Std shower valve cartridge?

[DIY_guy]

I have and old rental house and need to replace this old (20+yrs?) American Standard shower valve cartridge in the photos. To make this job more of a pain for whatever reason the last owner did not install supply line shutoff valves, so I have to turn off at hot water tank. Am hoping to ID the cartridge before I start pulling it all apart as I am concerned it's so old it may be discontinued, so any help is appreciated. Also, do I need to unscrew that chrome ring before I try to remove the cartridge retaining nut?

 

[arctic bill]

yes it is a cerimix American standard , was supposed to be guaranteed for 50 years . Came out in the 80's

 

[bawalter]

That is a thermostatic cartridge. OEM number is A954400-0070A.

I found it online at NYRP: American Standard A954400-0070a Cartridge (2043) Elite Thermos

I am sure others have it as well.

 

[DIY_guy]

Thanks guys for the great info, am I correct I that need to remove the chrome ring/sleeve too to remove the cartridge? Or just remove the retainer nut?