Don't want to be an alarmist, but that gap between the brake drum and backing plate looks a wee bit wide to my eyes. Compare that gap on the left side to the one on the right. Are they even? If so, then do like redmodelt described. But if the gap on one side is wider than the other, then it could mean that the thrust washers and spacers that hold the alignment of the differential carrier in place within the axle housing are worn out. This would allow the entire axle/differential assembly to move from side to side a within the housing, which could "pump" grease out past the axle shaft onto your brakes. I know this from experience. I had a wider gap on one side than the other with grease fouling the brakes on that side, even though I put on the modern outer cap with the seal. Last year my axle shifted while I was on a drive and the drive shaft pinion disengaged from the ring gear resulting in no brakes. The babbit spacer had crumbled to bits. I rebuilt the axle innerds this winter, and now the spacing of the gaps between the backing plates and drums on both sides is even.
