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Flare Brake Lines: A DIY with Photos

Replacing hard lines is part of maintaining your braking system (CN90).

Flare Brake Lines


polskamafia mjl » This is a short write up on flaring the rear hard line on the passenger side; it is largely a rehash of cn90’s thorough write up which can be found here.

Parts list

O’Reilly’s Auto Parts
Copper Nickel hard line (1):

Cu - Ni Line
Cu – Ni Line
IMG-0677.JPG

M10 x 1.0 flare nut (3):

Flare Nuts
Flare Nuts

Union (1):

Union
Union

Flare Nut and Union

Flare Nut and Union
Flare Nut and Union

Amazon
Neiko 20657A ISO Bubble Flare Tool

Bubble Flare Kit
Bubble Flare Kit
Flare Tool Instructions
Flare Tool Instructions

Procedure

I removed the old caliper and placed it in front of the hub so I had easy access to the hard line.

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Next I cleaned all of the grime off of the hardline using brake cleaner and sand paper.

IMG-0687.JPG

I began with the new section of Ni-Cu tubing and cut off the double flare that came on the line. After cutting the line I used a small file to ream out the inner diameter and remove any burrs. Next, I used a large file to chamfer the end of the brake line. Next, I made the first bubble flare on the Ni-Cu line. I used this as the caliper side.

Caliper end bubble flare
Caliper end bubble flare
Bubble flare close up
Bubble flare close up

Then I trimmed the Cu – Ni line to size using a tube cutter and once again cleaned up the end using a file as explained previously before making the second bubble flare. This end will connect to the old hardline thorugh the union.

IMG-0690.JPG
Ni-Cu line on the new caliper
Ni-Cu line on the new caliper

I installed the new caliper and screwed the union on to the flare nut.

Next I cut the old hard line along the straight section, slid the new flare nut on, and installed the brake flaring tool.

Old hrad line with flaring tool
Old hrad line with flaring tool

I used brake cleaner to keep the flaring tool as clean as possible and then made the last bubble flare.

With the old line flared I screwed the flare nut into the other end of the union and tightend both flare nuts.

Completed brake line
Completed brake line

Next bleed the brakes and check for any leaks at the union and at the new caliper.

Here’s a shot of the old caliper with the butchered brake line nut. So much trouble over such a small thing.

Old caliper with rounded brake line nut
Old caliper with rounded brake line nut

Conclusion

Overall it was a pretty easy process. Take your time and make sure you’re making good flares. I would also recommend using a pair of vice grips with rubber hoses over the jaws to pinch off the flexible section of brake hose on the delta arm. This should help reduced how much brake fluid leaks out of the hard line after you cut it. I would also recommend buying a spare piece of brake line to practice on before hand. For a general overview of the brake flaring process I found this video super helpful.

Flare Brake Lines

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