New squeaky rear brakes

[Bluebird]

R&R rear brakes. LHS drum replaced with new/turned. RHS drum in good condition/smooth surface, within reusable specs. RHS squeaking when brakes applied firmly. Why is this happening? Front pads are as thick as new (I compared with new set of pads), pads have 15K on them. Thank you all, for any diagnoses.
Have a Blessed Holiday Season, TDR
Patrick

 

[B.G. Smith]

When you install new linings in a used drum you have square edges on the shoes and rounded edges inside the drum, it will take a few stops for the shoes to wear into the new pattern. bg