So I was in the process of swapping pads, rotors, and lines and of course when I tried to remove the front aluminum calipers (05 STI) I stripped all the aluminum threads out. I attempted to fix them with time-serts (fancy helicoils) and ended up drilling the holes slightly crooked. I did this on a drill press and tried my best to make sure the holes were square, but somehow they came out being what looks like a degree off. I went ahead and installed the inserts anyway and you can see that the bolts are not quite perpendicular with the face of the holes.
I tried bolting the caliper back to the knuckle, and it seems to bolt up just fine. I'm obviously trying to avoid buying a new caliper so I'm wondering if any of you ran into this problem or have any insight. I went ahead and took the other caliper to a professional machinist to drill and tap the holes so that one should be good.
I did use a level and checked it multiple times, but I guess I didn't hold the caliper enough and it moved. It looks alright when its bolted up to the knuckle. You can't really see any gaps, but I'm guessing the bearing surface under the head of the bolts is not seeing an even load which may cause the bolt to vibrate loose after a while. I'm leaning towards just biting the bullet and getting a new caliper. If I do that, I'm not sure if having a new caliper on one side and an old one on the other will be a problem. My car has less than 60K miles on it though, so the older caliper hasn't seen that much wear and tear.
Using a new and old caliper is not a problem. That's said if it bolts up OK then try it. If it gives you a problem then replace it. They make oversize Timeserts you could try too.
If it makes you feel any better I recently rushed to drill a front caliper when I was very tired, alone and with poor light. Ended up trashing a front caliper. Your holes look good compared to mine! Expensive mistake. Last weekend I did my rears and had another hole to repair. I waited till I had assistance, proceeded very carefully and everything went smoothly.
Some tips for others:
* There is not much flat area to rest the caliper on.
* Mine both had burrs left at the edge of the hole. My calipers would not lay flat until they were removed. I drilled them off. A file would have worked too.
* Your calipers are very very soft! Don't count on the drill following the old hole! Get everything properly lined up first!
* As Law mentioned if you are using a drill press then level the platform.
* You'll probably need a die to clean the bolt threads.
* Check your bolts to be sure that are straight. Fronts are long, more prone to being bent and their straightness is more critcal than rears. I replaced my bent on when I replaced the caliper.
Its not difficult but you really don't want to screw it up!
Pretty sure loosing that much thickness won't be an issue. If it were that close to failure it would be prone to worse problems than we now have with them!
In the case of your current Timeserted caliper, the only thing I'd be concerned about is to have a new bolt ready (it took a day longer to get new bolts than it did the caliper) if you remove the it again in case it has bent to conform to the threads.
I'm not sure anybody knows for sure what the answer is to this. I don't know of anyone on the forums that designs braking systems for cars. With that said I would personally bolt it up and see how it looks. Some light street driving while checking to see if the bolts back out. You're probably fine.
I did timeserts on my front calipers a couple years ago and I know for one of them I did not get them flush with the mating surface but it was straight. That has lasted fine for a couple years with 8+ hours of track time. I agree with above if it looks alright bolted up just torque them proper maybe a bit more and then just include it in a list of things to check before events. I think if you drive it for a while and don't notice any abnormal rubbing/wear and the bolt is still torqued to spec I wouldn't worry about it too much.