I have a 2004 Sebring sedan with rear drum brakes, is it possible to convert to rear disk brakes?

At a junkyard near me there is a 2004 Sebring convertible with rear disk brakes, would parts from it bolt on?

I would need, the hub assemblies, calipers, rotors, brake lines, pads, maybe parking brake cables?

 

Add to that a proportioning valve if you don't have antilock brakes, maybe a new controller and sensors if you do have antilock brakes.
I doubt if anyone has ever done this as the amount of work and expense far exceeds the value of the finished product. As a result, you are going to be the pioneer here.
Take lots of pictures and write it up when you're finished as a photo album.
Oh, yeah, keep your insurance paid up just in case it doesn't quite work out.

As to your basic question, it might be possible. The rear suspension is essentially the same. Measure everything carefully before you start, proceed slowly. You might be better off to scour the junkyard for a sedan. Lotsa luck.

 

I've done this before on an older Altima, but the Nissan forum had posts by others who had already done it so I knew everything would fit. on the Altima, as on the Sebring, it would be using parts from a car with ABS to one without ABS.

Why would I need a proportioning valve, isn't there one already?

I don't want to be the pioneer on this so I will probably not do it. I was hoping someone had already done it, and could verify the hub assemblies bolt in, i.e. all the rear arms are the same.

 

The proportioning valve for a disc brake car may be different than for a drum brake car. I don't know that specifically but given the differences in the systems, it would not surprise me at all.
I've seen discussions by people who have done this on Ford Taurus vehicles, but have never seen anybody here discuss it.
You might check in over on the Chrysler Sebring Convertible Club website. There are some people over there who have done some weird things.