1st try to adjust the hinges, if that is possible remember to adjust ALL of them, otherwise they will start to bind. If there are no adjusters and with the mech in the locked position, try to mark the bottom of the bolts/hooks ect with a pencil on the frame, sometimes this is not posible but if it is, then it will give you some idea of which keep is out or how many and by how much. If that is not possible, then it by trial and error. E.G:
If the keeps are individual, that is to say, not in one long strip, then I have found that in most case's it will only be one keep that is mis-aligned. Start by removing one keep and try to lock the door, if that solves the problem, then that is the one to move, 99% of the time it will be down, by just a few mille as doors tend more to drop that raise. If after you have removed one keep and it still binds, then leave that keep out and remove another keep and follow the same procedure, if that solves the problem, then replace that keep a few mille lower, then try it and if that is ok then replace the 1st keep to it's original position and try to lock it again, if it locks ok then leave it, if not move that one down a couple of mille. If it is in one strip and you have looked at the hinges and there is not adjuster's, then you have to toe and heel it.
On average I replace/repair 9 or 10 a month ( on a good month) and have found nearly all need adjusting, the reason most have failed in the first place is because the door has gradually dropped and the mech has become more and more harder to lock, instead of getting a locksmith in to adjust it, they use more and more effort to lock it and surprise surprise...it breaks. How many times have you fitted the new mech and the customer say's " oh, thats better, before I had to really struggle to lock it"
I hope this has been some help to you....All the best Steve
