Time-Sert Repair of Caliper Mounting Hole

This is the 2nd time I've had to do this on this car, so I figured I'd document it. The bottom line is, if you can get the old bolt out, you can do the repair on the car. Some tips and tricks will ensure it goes well. Let's get started: While removing my RR caliper, the top bolt came out like it was buttered, but the bottom one was pretty seized and required some heavy use of an impact gun to get it out. Afterwards the threads didn't look so good, and definitely wouldn't support the specified torque anymore: Time for a Time-Sert. The one you want is M12x1.5 thread x 16.2mm length. My research makes me feel like it's a better solution than a helicoil, and the installation kit is reasonably priced. The process for doing it is quite idiot-proof, IF you get everything nice and square as you go along. I made a drill guide out of a scrap piece of aluminum. The drill size for the M12x1.5 Time-Sert is 0.484", which is slightly larger than the bore in the caliper. Otherwise you could probably use the caliper as a drill guide, but you'd scar it up a little. My drill guide has two 1/2" holes spaced at 130mm apart to give just a little clearance for the .484" bit. Use both bolts to align it nicely, tighten the top bolt snug so nothing will move, and then remove the bottom bolt. Now use your cordless drill and the bit supplied in the Time-Sert kit to remove the last vestiges of the wrecked thread. It's key here to have a very compact cordless drill, otherwise it won't fit in the fender well. If your drill is longer than about 7", it ain't gonna work. Beg/borrow/buy/steal one to avoid having to remove the upright! After drilling, most of the ruined thread is gone, and you're prepped for the other machining steps to install the Time-Sert: The next step is to counterbore the hole for the flange on the Time-Sert. The kit comes with a pretty idiot-proof tool that aligns itself pretty well and bottoms out on a shoulder when it's deep enough. Line it up good, spin it until chips stop coming off, and you're done. Here's the hole after counterboring. The light rub marks around the hole are from the counterbore tool's stop shoulder rubbing on the face: Next step is tapping the oversize thread for the Time-Sert. I probably should have used another tool to keep it square to the hole. Fortunately I have tapped about a million holes in my life and I'm good at starting taps square. A spare piece of pipe of the proper diameter would be a swell tool here to square it up, or even a scrap of 2x4 with the right-sized hole drilled through it. If you get the tap crooked, you're up a creek, so take your time here and get it started right. Once it's started well, it will stay on course. Use plenty of oil to keep the tap lubricated, and back it up every 1/2 turn or so to break the chips and avoid getting it clogged. If the tap ever feels tight either while advancing or retreating, STOP and turn it the other way first. I removed the tap 3-4 times along the way to clean it, blow chips out of the hole, and re-oil it. It pays to go slow here and make sure you don't get the tap jammed, or worse yet, snap it. If you screw up at this stage, you have no recourse but to admit defeat and jump off a cliff. Take your time! And here's the freshly-tapped hole: Most of the scary parts are over now! We won't be removing any more material. Time to put our new Time-Sert in: Thread the insert in by hand until it won't go anymore: Put a few drops of tapping oil or motor oil on the insertion tool, and run it in by hand until it stops: Use a tap handle to keep turning the insertion tool. The Time-Sert will go in until the flange on it bottoms out on your new counterbore. The tool will then continue turning pretty freely until it gets most of the way through the insert and starts flaring out the bottom few threads to lock the insert in place. It will tighten up about here: Since this is a thru-hole, not a blind hole, you can run the tool right on through until it pokes out the back of the hole, and then unscrew it back out to remove it. Repair complete! Bask in the glory of your nice new steel threads! Install your brake caliper with some anti-seize on the bolts, torque the bolts to spec, and move on with life knowing the current retail price of the knuckle you just saved is around $600, and would take a huge amount of labor to remove and replace.

Nice pictorial and tips along the way. Just did this replacing front knuckles/bearings for a C4S. Used helicoils so I could use a smaller bore, but I like the timeserts. This is may be controversial, but I was told to use antiseize, and did as you did, to avoid removing threads the next time.

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Yeah, I track my car routinely, and checking caliper bolt torque is part of my pre- and post-event checklist, so I'm not too concerned about them gradually backing out over time without me noticing. I'm more concerned about not being able to get the bolts out for the next rotor change. So for me, anti-seize it is.

Nice work. Timeserts are handy and much better than helicoils IMO.

And here's what I did on the other side when the bolt snapped!! The bolt backed out about 1/4" or so and then tightened up irreparably No amount of forward-and-backing with the impact wrench would free it, so eventually I just went at it with a cheater bar and snapped the head off the bolt. After that, it was easy enough to remove the caliper and rotor However, this is a lot harder to clean up than just a mangled hole: With a welder maybe it would be possible to weld a nut to the remaining stud and twist it off, but based on how this tightened up I'm not sure even a 6' breaker bar would have gotten it out. So, my approach was to cut off the majority of the remaning stud, and then drill out the part still in the hub carrier. Step 1 is to put a washer over the stud so that during sawing I don't damage the caliper mounting surface. This has the 2nd added benefit of leaving about 1/8" of the bolt proud of the surface, which gives something for my drill guide to align to once I start using it. Then go to town with your cutting device of choice. Angle grinder, hacksaw, reciprocating tool, whatever works: The key to drilling out the remainder is to get the drill started on center. That's 90% of the battle, and then you just patiently drill out the remainder. I used the same drill guide as above, and turned a small collar to fit around a centerdrill to get started. Recall that my drill guide has 1/2" holes, so I made a collar about 0.495" OD for a slip fit, and then made it about .005-010" oversize on the center drill. I could also have made another drill guide with the proper diameter for the centerdrill, but that would have wasted more metal Also with a smaller hole, the drill guide wouldn't fit over the small amount of stud sticking up after cutting above the washer. So I think this method works nicely. Using a centerdrill to start is key since it's super stiff and will stay on course rather than bending and potentially wandering off course like a normal drill bit. This assembly slides into place nicely in the drill guide and ensures a perfectly centered start to the drilling operation: Once that makes a nice start on the screw, then it's just a matter of drilling out the remainder of it. Low RPMs and plenty of cutting fluid keeps the drill bit cool and happy. If you're seeing smoke or fine dust coming off, that's bad and you should slow down, or use more lubricant. You want to be seeing nice healthy chips. A uni-bit drill bit worked nicely to step through the material one diameter at a time, although you can't get all the way through with that because it's too long and pokes into other features of the hub carrier on the backside of the hole, so you have to finish with a straight drill bit of appropriate size. Once all the screw material is removed, than it's a re-do of the Time-Sert procedure detailed above. A hassle indeed, but in the end much easier than having to remove the whole hub carrier from the car since that would involve dismantling the parking brake, the complete suspension, axle bolt, etc. On-car jigs are better! So, if you're removing a caliper and you feel that awful tightening sensation, don't sweat it! Wrestle it out with an impact wrench if you can, or snap the head off with a breaker bar, and then proceed with one of these repairs!

they make caliper studs to prevent thia from being an issue so if you are taking your calipers off a lot, might be worth the money

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Do you have a good source for these? I have seen some for sale, but they are obscenely expensive for what they are.

well, yeah I can't argue with that. tarrett seems to be the only source at roughly $130 per axle

We time sert all the new 991/981 GT cars we work on that are seeing track use, it is a no brainer to ensure safety and reliability of the threads when doing pad changes on a consistent basis

nice work!

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Why not do a stud conversion instead? Just wondering

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Preference of our technicians. In combination with Spiegler SS lines its easier for them to maneuver the calipers on and off for pad changes

Nice job dk! Patience pays dividends on repairs like this. When I was younger, I would always rush jobs like this, and make more work for myself. I see you've got some machining skills. That sure goes a long way too. Learned many lessons making chips. Thanks for sharing.

This is a great guide that has given me confidence to fix the threads on my 996 C4S myself! Could of questions: I don't have access to a drill press to make a drill or tap guide, and don't have OP's machining experience to confidently get the tap square myself. Any thoughts on using a drill/tap guide like this: Amazon Amazon I saw this this wurth video where they use a tap handle for drilling and counter-sinking as well. Any reason not to do that? Thanks!

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Job completed successfully, twice over! Once I finished installing the timesert in the upper bolt and started to torque the caliper on, the lower threads gave in as well. Second one was much easier. I ended up using a ratchet with the drill bit (with a jury rigged 3/8� square adapter) since the provided bit kept slipping in the drill chuck. The drill guide helped but could have done without it as well. The cordless drill was perfect for the countersink. And then I did the tap by hand. I used the tap guide for initial alignment till I was 3-4 threads in. And then took it slow. Half turn in, quarter turn out. Removed the tap to clean the shavings 2-3 times. And lots of cutting oil. In my first go, I made the mistake of not completing the counter sink all the way, which prevented the insert from fully seating. I was luckily able to unscrew the insert by hand, finish the counter sink, and then re-chase the threads to be safe. I oiled both the insertion tool as well as the outer threads of the insert. I did not use anti seize on the caliper bolts. Glad to have the car road worthy again. The time sert kit is 100% worth it if the caliper bolt threads look worn at all. I�m actually debating going back in and installing inserts in the other 3 corners.

Good stuff! Congratulations to you. Not easy to drill perpendicular to the surface.