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This past weekend I experienced again something that has happened to me once before - I get a massive taper worn into the front brake shoes. The inside edge (against the backing plate) got wore almost to the liner, while the outside edge looks almost untouched. The top shoe more then the lower, but there is still some taper on the lower shoe as well.

They were new shoes. The ones I took off were fine, so it's not a backing plate staightness issue. This happened once before, and I never understood why. Any ideas?

My first thought would be bent backing plate, but you covered that. Just for clarification .. what shoes are we talking about? CT ? New/old? something else? Same brand as "happened before" and/or "normally doesn't happen"? Were they brand new this weekend ... or xx weekends old? (how long did it take for them to wear to that point?).
Oops - now I see you said they were NEW. I'm trying to visualize something that would HOLD the brakeshoe at an angle. I'd think that normally, the shoe would square up against the drum ..unless it is HELD at an angle some how. Only way I can think of for that is VERY tight fit on either the adjuster or wheel cylinder ...... or pinned to a bent backing plate somehow (too tight a spring?).

Steve, FV80

I've had the problem with 2 different compound brake shoes. The first time was about 3 years ago. I put a new set of shoes in and thye wore fine. I haven't changed anything else related - same backing plate, same drum, same cylinder, adjuster, springs, ect...then all of a sudden this last set did it again.

Everything looks normal - I can't find anything wrong. My theory now is the hold down spring was too soft. I use a screw through the spring instead of the pin, so I can adjust the tension. I might have had it too soft. If it's soft then any little thing can cause the shoe to rock a bit. I'm going to put more pre-load on the spring this time and see what happens. It's very bizzare though. I was just curious if anyone else ever had the problem.

Mike, this post is a bit late but I just got back into the country but look at the contact areas on the backing plates and make sure they are smooth and free from wear grooves. Grind or sand to make smooth again.

Mike

I agree with Brian. The area where the shoes actually contact can develop a burr that can be removed with a file. The shoe will catch on the burr and will not return.

Matt

Mike,
In light of what you have said, I am more suspicious of the shoes. I would check squareness of the lining to the mounting "blade" (couldn't think of anything else to call it), along with the distance from that "blade" to the edge that rests against the backing plate.
Mike P.