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As a part of the breaking system overhaul I've been working on with a buddy on his C4S we've hit the dreaded stuck flare nut snag when installing new stainless brake lines. As luck would have it, all corners went well except for the driver rear. It's quite common for these to corrode and break - here is the odd issue we ran into...
Before touching any break like fitting I sprayed them down with some PB Blaster and used the special flare nut wrenches. On the driver rear, I was able to successfully loosen one end of the rubber line buts but the one closer to the caliper was so stuck it would not budge and any extra force was going to strip it. Next step was to loosen the hard line connecting to the caliper to remove the whole thing and then separate the rubber line. It seemed like the flare nut started coming out but at one point it just continued to spin in place - great... While loosening it, I would move it lightly in both directions to keep the threads in good shape but seems like the corrosion was bad enough that this didn't help. With the caliper off and the hard line cut (ordered a new line) to get better access I tried using vice grips to turn it while pulling up but no luck. The flare nut just spins freely and even moves slightly up and down but wont budge any further. Other than gripping it with vice grips and drilling it out are there any tips anyone has? The end goal is to get the f***er out and either chase in new threads or probably install a helicoil with fresh ones. Seems like the thread size is M10 x 1.0.
The problem is not so much removing the flare nut and repairing the threads, it will be doing so without damaging/affecting the internal inverted flair.
The likely outcome will be replacing that caliper...
The problem is not so much removing the flare nut and repairing the threads, it will be doing so without damaging/affecting the internal inverted flair.
The likely outcome will be replacing that caliper...
Agreed. New caliper is the back up plan. My goal is to drill the flare but out enough to be able to break it up and remove that way. Hoping this will prevent any internal damage. The flare but moves freely when rotating and about a mm or 2 up and down. I want it held up by vice grips when drilling, if possible.
Maybe try a "nut splitter", hold the fair nut up and use the nut splitter, if you're lucky, it will split all the way down and you can "crush" the hollow flair nut back in on its self . less likely to damage the internal flair that way ..
Not a bad idea! Will add that to the list of things to potentially try. Thanks Skip! I agree that collapsing it to the inside would be the safest way, especially that. it's already partially loose.
Well, after 2 days of on and off drilling and several broken bits I got the bastard out. I think I'll be able to use the caliper and will just need to clean up the threads. @Porschetech3 or someone, would you be able to confirm what is the thread size/pitch on those flare nuts? It seems like it's M10 x 1.0 but not in a position to guess here.
It is 10mm x 1mm size but the bottom of the hole is a taper that you cannot scratch at all or it will not seal.
Awesome - thanks! And you're right. As the bolt was being drilled out the hard line was still in place and needed to be drilled out as well which made it a challenge. Luckily, the bottom tapered portion of the hard line was in place protecting the hole and I was able to just remove it with a pick once I removed enough of the bolt. Once new threads are in it will be cleaned with compressed air and rubbing alcohol.
Get a Piece of brass or aluminum rod that loosely fits in the hole. Cut a thin “coin” and drop it into the hole before drilling and tapping. This will give some protection to the sealing surface at the bottom.
I have successfully used that hack twice now when installing helicoils in aluminum calipers.
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Stuck caliper flare nut removal help
