Ilbranteloth
Explorer
If you're doing weapon breakage, I would:
1. Only have the weapon have a chance of breaking on the first attack each round. Otherwise you run into the weird problem that skilled warriors (= multiple attacks) break their weapons more often.
2. Connect breakage to the attack roll rather than the damage roll, because if you do it the 2e way of having it potentially break on a max-damage roll, you get the weird effect of a greatsword only breaking once in a blue moon, while shortswords are fragile as heck (while realistically, it ought to be the opposite - the longer weapon should be more likely to break). A suggestion is to have it potentially break on a crit - not on every crit, but a crit would trigger a roll for breakage.
That's what I use, you make a weapon break check on a critical hit. The DC to avoid breakage is very, very low. DC 4 for steel, DC 6 for wood, DC 7 for stone, and DC 8 for bone.
I use the Rust Monster concept that each time a weapon is damaged it takes a -1 penalty, and at -5 it's broken. But some weapons (such as orcish weapons) have fewer steps, like a -3 is broken.
The exception are bows and crossbows, where you make a weapon breakage check on a natural 1 instead.