Huck brakes (which your rig almost certainly has) need some "wear-in" time with new linings, and you'll need to do frequent adjustments until the linings wear into full contact with the drums. That's particularly true once the drums wear a little oversize. Here's a sneaky trick to shorten the wear-in process a little. Glue a piece of coarse sandpaper, like 40 or 60 grit, to the inside of a drum with the abrasive facing in. Use water soluble glue like original Elmer's, or even library or wallpaper paste. Scuff the new brake linings against the sandpaper to match the radius of the lining to the drum. Then use boiling water to melt the glue. It will shorten the wear-in process dramatically.
Jerry
