I am the most recent victim (self-inflicted of course) of the alternator tensioner bolt. Heard some chirping, went to tighten the belt and the bolt snapped in the middle. I've installed a new one and I can tell the cap nut has already destroyed the threading... that said, it's on and adjusted for now.

Now I'm no stranger to the adjustment process. I have a copy of the FSM and loosen all requisite bolts before spinning the tensioner.

While I was in there, I pulled all the belts. All three were Gates brand that I installed new 3 years ago (about 40k miles) and both the power steering and A/C belts still looked new. The alternator belt was cracking and had a few threads loose on the sides.

The FSM states that all belts should be tensioned to 40-45kg.
Here's the thing. The PS pump at maximum adjustment gives me belt tension of only 25kg. The AC compressor at maximum adjustment also gives me 25kg on the cricket. The alternator is the only belt I've been able to adjust to 40kg.

All the sizes are correct (1030, 875, 1145).

Have I been over-tightening the alternator belt? Is it important to maintain belt tension balance? In other words, better to have all belts at the maximum tension of the loosest belt (25kg)?

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1981 240D 4sp manual. Ivory White.