one final thing to note, you must retain the aggro of the thresher by walking in and out of its attack range. if you stay in cover for too long, it will back up and actually ambush you from behind or when you move around to regain aggro. i learned this the hard way, then promptly destroyed it on my subsequent try. good luck!
Threshers have a bunch of small critical points, so use weapons that hit an area instead of a single point to kill it quickly. I had a decent shotgun and killed it in about 6 hits, grenades should work well if your weapons are terrible.
Just dual wield 2 explosive miniguns and completely annihilate him off the face of pandora.
oh wait... It seems no one plays salvador but me.
Double shotguns. i have one that fires 4 shots at once before reload, but with the proc chance of not using ammo i can get 7-12 shots in a row semi regularly.
Second shotgun i can fire 17 explosive rounds per shot, one shot a second, 4 shots before load if no procs.
I triggered gunzerker did some damage got point blank, went into last stand, and commenced to decimate him with my main "single shot" shotgun. nothing like firing 7-12 shots in the blink of an eye thanks to stupid high fire rates.
It's a suicidal play style but with the right skills you rarely ever stay "dead" for more than a second :D (mind you, playing through with a friend, if this was solo it'd be even easier.)
Flub, your strategy worked perfectly once I found the place, many thanks, I likely would have been frustrated for hours, I beat him by a hair, ran out of SMG ammo with him almost dead (my Fire and electric weapons were SMGs), got downed, and killed him with a second to spare with corrosive.