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DIY: Flaring your Brake Lines

Let’s talk Flaring your Brake Lines

Volvo Forum Member and Contributor Vjaneczko writes an amazing tutorial for DIY: Flaring your Brake Lines. Here’s what he said:

I have to start this with a quote from Queen Gorgo in the movie ‘300’:
“This will not be over quickly. You will not enjoy this.”

This started as a 10-minute job to replace the flex hoses for my front brakes and install a new caliper on the driver’s side. It tuned into a messy job involving several days of research and ultimately flaring the hard lines. Here’s what I learned along the way.

After 14 years in Chicago, my brake lines were frozen solid. Wrenches rounded off the nuts. Vise Grips shredded the nut. A blow torch did absolutely nothing. I had to cut the nuts and replace them.

Tools and Supplies You Need

  • Bubble flaring tool kit – not a single flare or double flare, but a bubble flare.
  • 3/16 in. tube size to M10 – 1.0 thread bubble flare European steel tube nut – one per line
  • Flare wrenches – 8 mm, 10 mm, 11 mm, 12 mm, 14 mm and 15 mm
  • Small hacksaw blade – no more than 3/8 inch wide
  • 3/16-inch tube bender
  • Small section of 3/16-inch tube – used for practice
  • A good supply of shop rags
  • Small bucket – to catch old brake fluid
  • Brake fluid – at least one 12 oz. bottle per nut you’re replacing.
  • Large bucket with soapy water
  • Safety goggles
  • Mechanics gloves
  • Power bleeder or a friend who knows how to push on the brake pedal.
  • Small tubing for bleeding the brakes. Length needs to go from the bleeder valve to the small bucket.

Flare Brake Lines Procedure

First off, this is going to be messy. Did I mention that already? Yeah, it needs to be repeated. Plus, the brake fluid makes everything slippery so I strongly suggest wearing mechanics gloves for this, to help hold stuff.

Flare Wrenches: I was surprised that I used so many sizes. I used 11 and 14 mm for the hard line to flex hose connection, 14 mm on the old flex hose at the caliper, and 10 mm for the bleeder valve on the passenger-side caliper which I did not replace. For the new drivers-side caliper, the bleeder valve was 8mm. The new flex hose itself used 15 mm at the caliper and 14 mm at the hard line connection.

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These are Flare Wrenches

Nut information: Pay careful attention to the nut you purchase. There are (at least) two nuts that have the same threading but are slightly different:

“3/16 in. tube size to M10 – 1.0 thread inverted flare Japanese steel tube nut”
“3/16 in. tube size to M10 – 1.0 thread bubble flare European steel tube nut”

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European (left) and Japanese (right) Nuts

I took my SS lines to the store and asked for nuts that would fit. I got the Japanese type, without knowing there’s a difference. The Japanese version is slightly longer than the European version, and the tip under the flare is shaped different.

Also, 3/16 line is also known as 4.75 mm line.

If you’ve never flared a line before, use the small section of tube and practice a few times. My first attempt was misshapen and I knew I had some more practice to do. After trying this a few times, try holding the pipe clamp in a position similar to what you’ll experience on the car, just to get a feel of how awkward it’ll be to twist the bolt. I did six before I felt good enough to try it on the car. Once you’ve done a few, you’ll get the feel for the tool and you can whip through them in no time. When I was done with each one, I inspected it mounted in a nut. I even torqued one down into the new flex hose so I can see what happened to the flare once it was inside coupling. This gave me a good understanding of where the metal was compressed/stretched and how it created a seal.

Flare Brake Lines, Preparation

First off, it would be a good idea to get the rotor and brake pads out of the way. This way, there’s no chance of fluid or scratches getting on the parts. In my case I was replacing the rotors and pads, so they were already off the car. It made it easier to get in there. The sway bar link was the biggest obstacle with the strut being next.

Remove the ABS cable and tuck it out of the way.

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ABS cable out of the way

Place a rag under the brake line where you’ll cut, and place the small bucket under that. This will help to catch the fluid that drips out, with the rag acting as a funnel.

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Rag & Bucket to catch the dripping fluid

Have a bottle of brake fluid near the fluid reservoir. You will have to top it off as you go, to make sure you don’t run dry and potentially mess up the master cylinder. My thought was that if the cap was off the reservoir, there would be less pressure in the system and the fluid would drain out faster. So I left the system capped during the cut.

Next, make sure all of your tools and parts are in reach as you’re sitting at the wheel well. You don’t want to start searching for something as fluid is dripping out of the system.

I STRONGLY SUGGEST placing the nut on top of the flaring clamp, just to make sure you don’t forget to put it on the line before you start the flare.

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Nut is on the clamp for a good reason!

I also suggest doing a ‘dry run’ by acting through the process, to make sure you see any problems that pop up during the real thing. I may have spent four times the amount of time to perform this process, but I wanted to make sure I did it right – I don’t ever want to be driving down the road and have to tell my daughters “Brace for impact!” because Daddy screwed something up.

First, begin cutting the line. Using the small hacksaw blade, begin cutting the line inside the spring, as opposed to cutting the line on the back side of the nut. Cutting on the inside of the spring will help improve the flatness of the cut as well as provide a little extra length of the pipe. Using a gentle pressure will allow the spring to help guide the blade in a straighter line as well as preventing the blade from binding as you cut. Once you cut the inside of the hose, fluid will start to leak out. Things will get slippery very quickly. Once you cut through the hose completely, the hose will spring apart and fling fluid around. This is where the safety glasses are important – you do not want that stuff in your eyes!

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Cutting the line on the inside of the spring clip

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Hard line has been cut

Use a file to smooth out the cut and use some steel wool to clean off the tube itself.

Depending on the bend of the tube, you’ll want to use the bender to straighten out the hose – if possible. Since my bender didn’t make it easy to straighten the hose, I gently straightened the hose by hand and then pushed and wiggled a nut up the hose. Vice Grips helped to firmly push while my other hand held the hose firm to prevent kinks. The tube has to be straight enough to get the nut, clamp and the length for the flare, so you’re looking to have about 1.5 inches straight enough for the nut to slide up.

Remeber to place the nut on the hose so the threads are pointed towards the flare you will create!

Place the clamp on the hose and check the gap for the proper distance from the end for the flare. When clamping the hose, start by tightening the nut closest to the hose, and then clamp down the far nut. This tightening doesn’t have to be painfully tight because of the clamp I used. It has small teeth inside the hole and will grip the hose very well. Use the twisting handle on the nuts and it should be fine. Tighten it too much and you’ll screw up your washers – which I did during my practice time.

Place the flare bolt on the clamp and tighten it, making sure to hold the clamp very still, otherwise you’ll place tension on the hose and possibly kink it. Take your time to make sure you’re applying steady pressure. When the flaring nut has stopped moving, you’re done.

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Flaring the hose

Once the flare has been made, do not remove the tool just yet. Since the fluid is not leaking out right now, check the level in the fluid reservoir and refill as necessary. Make sure you do not touch your paint or lean on your car as the brake fluid will eat paint. You can also take a moment to clean any mess if you wish. Remember, you’re only half done but you’re done with the hardest part.

Also make sure your caliper is within reach. Install the flex hose onto the caliper and place the caliper in its normal operating position. This is important so you can install the hose properly.

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Attach the Flex Hose to the Caliper First

There isn’t much twist available in the flex hose, so you need to place the end that connects to the hard line into the star bracket and screw the new nut into the flex hose.

Time to remove the flaring tool and bend the hose back into place. Take your time so as not to kink it.

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Carefully bend the hose back into placePlace the spring clip in position.

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Spring Clip in place and ready for connection

Insert the flex hose into the bracket.

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Grooved Bracket for Flex Hose

Remember; when you put the 14-mm flare wrench onto the end of the flex hose, it’s not to twist it, it’s just to keep it from moving. You will only be moving the nut you just installed.

Begin by holding the flex hose in position and pushing the new nut into it. Becase the spring clip is in place, it may take a bit of effort to get everything aligned and connected.

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Hoses connected – no more dripping fluid!

Once the nut was tight, I wiped up the mess with a soapy rag and dried everything. Next we check for leaks. Place a clean, dry sheet of newspaper under the hose connections. You can reinstall the rotor, caliper and pads if you wish, but I used a caliper spreader to hold the piston in the caliper and stepped on the brakes. Yes, there was air in the system but I wanted to pressurize the system to check for leakage.

With everything looking good, I reassembled the rotor, brackets, calipers and pads. Don’t forget to reinstall the ABS cable. I kept the newspaper in place and stomped on the brake pedal again for one last test.

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One last pressure test

Time to bleed. Using the Motive power bleeder was very easy and well worth the money. The only issue (and it’s a really small one) I could see in using it is when you’re done; you want to make sure you don’t overfill the reservoir. It helps if you start with the reservoir filled around the minimum level. When you’re done with the bleeding, tip the Motive bottle away from the internal hose so it’s not pushing fluid through the tube. Release the pressure on the bottle and top off the reservoir. It’s quite easy.

During the bleeding process, I discovered something odd. The bleeder valve on the old caliper had a 10 mm nut and on the new caliper it had an 8mm nut – both were Volvo calipers, but maybe the new one was rebuilt with a different valve. Although it was new, I still used a flared wrench for the bleeding process.

The final step was cleanup. Using the large bucket of soapy water, I dropped in all of the tools, gloves and rags I used to clean the brake fluid off. After I dried the tools, I sprayed them with WD-40 to prevent rust and wiped off the excess. I also used a rag to ‘swab the deck’ of any fluid that missed the bucket.

Nut information: Pay careful attention to the nut you purchase. There are (at least) two nuts that have the same threading but are slightly different:

  • “3/16 in. tube size to M10 – 1.0 thread inverted flare Japanese steel tube nut”
  • “3/16 in. tube size to M10 – 1.0 thread bubble flare European steel tube nut”

Read the whole DIY tutorial in the Volvo Forum: DIY: Flaring your Brake Lines

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