After finally getting hold of a set of HQ-WB rear backing plates to rebuild for the HK (damn things used to be throw away, try and find them now), when I pulled them apart I noticed the trailing shoe spring clips were a bit loose, and also the self adjusters which are located on the same pin were a bit sloppy. I thought it was just the springs had gone soft but once they were apart I noticed the hole in the backing plate were the pin head sits was concaved not flat like the other one. I looked at all the HK-HG backing plates in the shed and they were all similar. Found two more pairs of HQ-WB and a Torana set today and they were the same. As these backing plates are pressed symmetrical, and then have the handbrake and adjustment slots added afterwards, they should be the same on both pin holes.
What I had to do with mine was get them on an anvil and use a 12mm drift to bash them flat again. Otherwise the pin would sit maybe 2-4mm further towards the shoe which would mean the trailing shoe would be loose and so would the auto adjuster. I still think after the bashing that the steel is still about a mm or so shallower than it was originally, so I will probably put a washer under the pin head on that trailing shoe pin.
So when you go to rebuild your brakes next look at the rear pin head from behind. If it isn't flat like the front one and the steel under it flat you have the same damage as mine.
I bought all new pins, springs and clips for it. What does everyone use to free up the screw adjuster and keep it free? Is normal grease OK or should it be never seize or something similar?