Avid Elixer.....Front doesn't work.

dirttrax...like any brand/model of brakeset, they can have problems. Most new hydro brakesets that have a problem are usually fixed by a good bleed. Frankly I think Avids are one of the hardest brands to bleed...not undoable by any means...but many folks have a really difficult time. They were a challenge for me when I first experienced it, and I have a background of decades of automotive and motorcycle brake systems.

That said, you didn't mention how the lever pull was in terms of "distance". Does the lever come to the bar when you get this "wooden" sensation or what? Does the lever distance change? If the lever pull is short, strong, tight, and consistent, it sounds a bit like contaminated pads or such. You said you replaced the pads with semi-metallic units. Don't they already come with semi-metallic pads? On the famous Avid turkey-gobble-vibration deal, I did fix one of my Juicy and Elixir calipers with the application of a different brand of semi-metallic pads with an alloy backing, so yes, different pads and pad compounds can influence this. In your case, however, you seem to have a braking power issue that is either bleed or pad contamination related from the sounds of it.

Hey Will...this is weird, but in all of my dealings with bicycle brake systems, the issue of brake pad/rotor glazing has been almost nonexistent. It seems to me that most cases where that term was used were usually the result of pad contamination and not some form of "glazing". My understanding of "glazing" is where the actual pad material changes composition to the extent that this "altered" material builds up on the surface of the pad and/or rotor. I think this is quite rare except in cases where really high temps are encountered...and frankly most people do not reach that level of abuse, though many would like to think they do. I see glazing often misidentified when the real culprit is contamination from fork oil and chain lube as the primary causes. I've had brakesets achieve temps where you could actually smell the pad compound but almost never got any glazing. I know it can happen, but I've only seen it rarely. I did achieve this on Moab Rim trail some years ago when they had that chairlift setup there. I had 6" rotors on a Bullit, and they got hot enough to turn blue. I didn't touch them, and during next day's ride, the brakes started off a little weak from some glazing that had occurred, but just a short bit of riding worked that glazed material off in short order. I tend to think that most disc brakes will somewhat "right" themselves unless true pad contamination has occurred or there is air in the system. Pads and rotors are self-cleaning to a large degree without human intervention. Contaminated pads and air in the system will almost never fix itself.