It is amazing how cheaply you can buy the entire backing plate and fully assembled 12x2" brakes for these trailer setups. I paid around $45 each per axle (minus drums) for 4 complete new sets a few years ago on my 1991 Pace 24' trailer.
https://www.easternmarine.com/electr...ake-assemblies
https://www.etrailer.com/dept-pg-Tra...SAAEgKpuPD_BwE
Just last week I pulled apart the drums becuase I wasn't getting any brakes even though power was getting to them.
It turned out that from sitting, things just got a bit rusty and were binding up. Remember: this whole contraption works by engaging a magnet that then drags along the innner wall of the drum and moves a lever that pushes the shoes out. If there is too much surface rust on the inside of the drum, or the shoes are binding on the backing plate, it really reduces the effectiveness of that magnet.
Once I greased the backing plate contact points, greased the axle bearings while I was in there, too, and scuffed the surface rust off the inside wall of the drum, they worked good as new.
Just in time too! My daughter blew the transmission on her 2009 Impala SS (the LS powered front wheel drive version with the transmissions that were sourced from the V6 cars). She got 94,000 miles out of the original tranny so I was kind of expecting this one day. I was able to trailer the car all the way to the transmission shop 50 miles away with no problem whatsoever.