[PxTx]

I would start with a quick visual inspection. Take the drum off. Look dry? Peel back the dust boot on the wheel cyl- hopefully it is still dry. Compare the springs and such from the working side. Then check the adjustment and make sure both sides are close. If things look good, have someone hit the pedal and see if both sides engage.

So is this a recent development? What type of car is this... daily driver, show, barn find, etc?