OK, I'm going to rant because I'm at wit's end but I also need advice. I need to replace the accessory belt tensioner in my 2015 S60 T5 (5 cylinder engine), and, as anyone who has replaced this knows, f***ing Volvo, in some pencil-pusher's infinite wisdom, designed it so you need to use a T50 Torx bit to relieve the tension. When I tried to remove the belt the metal around that fitting broke, so I needed to cut the old belt off. Even though this f***ing Volvo has only 73K miles, I assumed that it happened because of metal fatigue. So I removed the old tensioner and installed the new, then, when I tried to turn the tensioner to install the new belt, that damned thing broke. Lightning struck twice. So I got another tensioner, installed it, and THAT one also broke at the fitting! A close look at the fitting on the tensioner shows that there is not much metal there. F***ing Volvo. Why couldn't f***ing Volvo have designed this so the mechanic could use a 3/8" drive ratchet (like nearly every other vehicle I have replaced Serpentine belts on)? The f***ing idiot who designed this damned thing should be shot!

All rants aside, I'd like to know if anyone has done this successfully, and if so, what trick did you use to turn the tensioner so it will not break, and how you got the belt on. I am using a T-50 bit with a 3" extension and a breaker bar so I can have some leverage. I also did my best to keep the breaker bar and extension straight. I and a friend have been trying to fit the belt over the alternator last, as there is no room anywhere else. Any advice would be greatly appreciated.
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Those look like they use a TP50 (torx plus) bit, not a T50 (classic torx) The TP50 has larger, rounder lobes resembling a cog instead of a star. Maybe this is contributing to your troubles? If possible, I would use no extension.