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Old 11-03-2005, 12:06 PM   #27
Scooby Specialist
Member#: 24569
Join Date: Sep 2002
Chapter/Region: South East
Location: East Tennessee
2004 Mazda RX8


I made a thread about this when it happened to my prodrive. Here is a copy/paste

Well, the threads stripped out of my caliper where the banjo bolt screws in. I was trying to stop it from leaking, which it somehow started doing during an autocross.

So after listening to some suggestions, I fixed it with a helicoil kit. I didn't even know that such a a thing existed before this problem. A helicoil is a small spring that you can insert into a stripped hole that will replace the original threads and maintain the same size.

Tools required:

2)Helicoil kit (will come with helicoils, specific drill bit, specific tap, specific insertion tool.)
3)Basic tools for attaching/removing brake caliper, lines, etc.
4)Vice grips

I have some pretty expensive brakes, so buying a new caliper is a bit of problem ($$$$). Obviously, if you have stock brakes, the best option would be a remanufactured caliper (and probably would not be much more expensive than the helicoil kit) - or you could consider this upgrade time. Also, follow my procedure at your own risk.

Here is what the caliper looked like. It would not hold any torque on the bolt.

First, you go buy a helicoil kit for your specific application (i.e. make sure you have the correct size). This will take some calling before you can find a place that keeps a lot of them in stock.

The size of the stock banjo bolt is 10mmx1.0 (thanks Scooby South!)

1) Use the application-specific drill bit provided with the helicoil kit to drill out the old hole.

**MAKE SURE that you go in straight when you drill. I would not got at it at with the full power of the drill, either - modulate the throttle. If you go in at an angle, the bolt will not mount flush with the caliper and you will be done - there will be no second chances and fluid will leak out everywhere. This means that your brake will not work.

**Also, when drilling, take your time. Don't drill the entire hole all at once. Drill a little bit, then tap out the shavings so that they do not get into the caliper. (I pulled out the vacuum cleaner, opened up the bleeder valves on the caliper, and sucked out the shavings) I did this very often. I took about 5 shots at getting the entire thing drilled out. This kept debris to a minimum.

2) Use the application-specific TAP that is provided with the helicoil kit to TAP new threads.

**Again, make sure you go in straight.

**Go slow and steady. You can use some cutting oil if you like. I just poured some brake fluid on it.

**I used vice grips as a makeshift T-handle on the TAP. A t-handle would be ideal as it will be tourqing from both sides. A vice-grip can get out of control if you're not careful as it is pretty heavy. Only attempt the vice grips if you have a steady hand. I would not use a power tool for this unless you know what you're doing (I didn't[know what I was doing])

**After you've gone all the way to the bottom of the hole, screw the tap out of there, and then run it back through once more, making sure you find the threads and are not trying to cut new ones.

You should end up with something like this and you will be ready to thread in the helicoil.

3) Clean up the hole, suck out the debris, etc.

**You cannot clean up the caliper enough. MAKE CERTAIN that there are no large pieces of crap that will damage the inside of the caliper.

4) Thread the helicoil into the hole, using the supplied insertion tool.

**My kit came with a "pre-threader" that helps get it started for fine-thread applications. I could not get the helicoil in without this accesory.

**I didn't use the entire helicoil. I only used enough to get down to the top of the fluid passage holes in the caliper. I left some of the helicoil sticking out and trimmed it with snips.

This is the final product:

After this, I sucked it out one more time and test fitted the banjo bolt. It worked perfectly. According to what I've heard. The threads should now be stronger than new.

Here is a link with more info about helicoil and how it works: Helicoil Information
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thrdeye is offline   Reply With Quote