I recently fixed a problem. The rotating cup on the cylinder has teeth all around it that get turned by the adjuster wheel on the backing plate. I had welded the backing plate adjuster wheel to the backing plate adjuster shaft on the drum side, as these are just peened and it was loose. The rotating cup on the cylinder was not perfectly round and the hydraulic movement of the cylinder was forcing the cup into the weld of the adjuster and jamming.
Check yours for clearance.
