Help! Broken brake caliper bolt

When tightening the two bolts holding the brake caliper to the knuckle/hub, one of the bolts broke off. I was able to drill through it after 4 hours! Ez out bit broke off too. Any ideas? I've doused it with PB Blaster but it won't budge. Could a drill press work? I have access to one tomorrow. Can the knuckle be re-tapped or is it hardened metal?

Thanks...really in a bind since its a daily driver.

 

Knuckles are cast. Not sure, but probably steel (instead of aluminum) because it's a truck. If you can use a drill press, I'd say go for it. Step it up slowly and you should see part or all of what's left of the bolt let go, leaving the threads mostly undisturbed. Run a thread chaser through it, and you should be good!
Failing that, open it up because yes, you can re-tap the hole

 

One issue is I just figured out the bolts are M12 x 1.25 which is not a very common tap size. What size drill bit should I use on the drill press?

 

3/8 is slightly smaller than 10mm. I'd stage it to there and see if you can get the remnants out. 7/16 is roughly 11mm if it needs one more step. This is assuming you want to try to put the correct bolt back in.
If you just want to open it up and tap it standard, use whatever is recommended in the tap set. They usually have a chart of hole sizes

 

My only concern with that is that the bolt still has to fit through the caliper hole, which isn't threaded, but the 12mm passes through with little room to spare. I have a tap set from Harbor Frieght. Will it do just fine?

 

Your tap set may do fine- it depends on how extensive it is. You'll need to see if it has that tap in it.
If you need to go standard, you could open the hole in the caliper a little more so your new bolt passes through

 

Well I got the bolt out after drilling and drilling with a drill press, then using a tap. After putting things back together, the ABS sensor light is on now intermittently. Are they very delicate? All I did was remove it from the hub then put it back together afterwards. Any ideas what might have caused this? Maybe it got some dirt on it?

 

The ABS wires are fragile to say the least.

 

How fragile? All I did was unplug it and move it out of the way, then plug it back in.

 

Since they are a magnetic pick up, check that there's not a small chunk of metal embedded.

 

You have pictures??

 

Great point. We were drilling metal so some of the shavings could've gotten on the area. I'll check tonight.

 

If that's all you did, you should be OK. It's possible to pull or stretch the wire while working near it to the point you'd break it.

I'd try and reset. Just disconnect the battery for 15 minutes or so.

 

I crawled under, took it out and wiped it off with a rag then drove around. The light has yet to come on. Never realized how $$$ these sensors are after looking

 

Cool. Easy fixes are always good.

Oh. And the bolt. Did you notice it's a 12mm with a 17mm head?

 

I had to call the dealer. They said it was an M12 x 1.25 flange bolt? I'm no expert with that stuff. Tractor Supply had one similar, not a flange though and longer. It worked. Definitely not a common size.

 

Glad you were able to remove the Ez Out bit! Those are usually hardened so when you break them they are hard to drill out, you could have broken it with a punch...

M12 x 1.25 are easier to find in Canada

For those of you who are interested, the Tap drill size for M12 x 1.25 is 27/64"

 

The stuck bolt piece rounded the EZ out bit like butter before breaking. What the hell are the bolts made of? Good point on the tap drill size haha. We went up 7/16" before tapping the new threads.

 

The bolts should be 9.8 hardened steel. Very tough to drill out if broken. Glad to hear you got it out. Snap-on does make a broken ez-out extractor set, which does work nice. But it's a pretty expensive set. I hope you put some anti-seize on the bolts. Keeps the rust away so they come out easy next time.

 

It's only .016" more, it's a lot for some stuff, but I guess you'll be fine

Like nitrowrench says, you could put some anti-seize too, but for caliper bolts i would go with blue loctite (242 or 243). It seals against rust (since you have less thread depth with 7/16" drill, thus more gaps between threads) and acts as a lock washer, it won't go out... And it is easy to remove afterwards!