Fabricating Custom Steel Brake Hard Lines and Relocating the Proportioning Valve (Honda EG/EK/DC2)
Introduction
Bending and flaring your own steel brake hard lines lets you re-route the system cleanly around an engine swap, a wire tuck, or a relocated proportioning valve on a Honda EG/EK Civic or DC2 Integra. This guide covers fabricating 3/16-inch steel lines from start to finish: choosing materials, cutting, bending to follow the factory routing, fitting the correct nuts, and forming proper 45-degree double flares that hold full system pressure. It also explains why brake lines must be double-flared and how to move the proportioning valve without upsetting front-to-rear balance. Because the proportioning valve reacts only to hydraulic pressure and is unaffected by gravity or orientation, it can be mounted almost anywhere, which is handy when a turbo manifold or other hardware crowds the stock location. Brake work is life-safety work, so treat every flare and fitting as critical and test carefully before driving. Adapted from a community writeup by blackEK on K20A.org (https://www.k20a.org/threads/my-brake-system-write-up-get-comfortable.23063/), including corrections from the follow-up discussion.
Reference
Tools Required
- Tubing cutter
- Tubing bender (e.g. O'Reilly part W80674) or a broom handle clamped in a vise for tight bends
- 45-degree double flaring tool with adaptors (e.g. Snap-on part TFM5A; budget kits from Harbor Freight also work)
- Flare-nut (line) wrenches to avoid rounding fittings
- Bench vise
- 12-gauge wire or the factory lines for mocking up bends and lengths
- Deburring tool or file
- Brake bleeding equipment
Parts Required
-
3/16-inch steel brake line (e.g. O'Reilly part BL360, sold in straight lengths)
-
Factory 10mm metric brake nuts/fittings (reused from the original lines)
-
Proportioning valve (factory unit, relocated)
-
DOT-spec brake fluid for bleeding
Safety Warnings
- ⚠ Brake lines must be DOUBLE flared. A single flare is not strong enough to contain brake pressure and can fail; one builder (bads2k) single-flared his lines with a 37-degree tool and had to remake them entirely.
- ⚠ Single flares belong only on fuel, coolant, and transmission cooler lines, never on brake lines.
- ⚠ A 37-degree flare is only for AN fittings; do not use it on standard steel brake line with factory-style fittings.
- ⚠ Label every line into and out of the proportioning valve; a mismatched circuit will not distribute pressure correctly and compromises braking.
- ⚠ Always bleed thoroughly and verify a firm pedal, then test at low speed before driving, after any brake line work.
Step-by-Step Instructions
1 Plan the routing and choose a proportioning valve location
Decide where each hard line will run and where the proportioning valve will live before cutting anything. Since the valve operates purely on hydraulic pressure, its mounting position and orientation do not affect how it works, so you are free to place it on the subframe, under the battery, behind the firewall inside the cabin, or wherever routing is cleanest. Before disturbing the original plumbing, sketch the valve and every line feeding into and out of it so each corner stays on its correct port; the front-left circuit must land on the front-left port, and so on. A miswired valve cannot balance the brakes.
2 Gather line, fittings, and flaring tools
Buy 3/16-inch steel brake line in the longest straight length available (for example O'Reilly part BL360, around $8.46 each) plus enough pieces for every run. You will also need a tubing bender (such as part W80674) and, critically, a 45-degree DOUBLE flaring tool with its small crush adaptors; a Snap-on TFM5A works, but an affordable double-flare kit from a discount tool store is fine for a one-off build. Make sure the tool flares fractional/standard line, since 3/16-inch is a fractional size. Plan to reuse the car's factory 10mm metric nuts rather than the loose-fitting nuts that ship on the new line.
3 Cut each line slightly long
Measure against the routing you planned and cut each piece a little longer than needed so you keep slack for adjustments and for the flares formed later. Run the tubing cutter slowly and steadily; a patient cut stays round and square, which matters for a clean flare. After cutting, deburr the end and confirm no metal shavings remain in or around the bore.
4 Bend the line to match the factory routing
Work one line at a time and use the original factory line as a template for shape and length; mocking a run with 12-gauge wire first also helps. Any bend is acceptable as long as the tube is not kinked. A cheap bender is fine, and a broom handle clamped in a vise gives you leverage for tighter radii. If you do kink a piece, do not scrap the effort: keep it as an accurate mockup, then bend a fresh length to the same shape and seat it into place.
5 Slide the correct nuts on before flaring
A flare traps its nut permanently, so install fittings now. Reuse the factory 10mm metric nuts, because the fractional nuts supplied on the 3/16-inch line seat too loosely to seal reliably (a correction contributed by CRXbart). Set the short 3/16-inch nuts aside; they may be useful elsewhere in the build. Double-check that each nut faces the right direction before you form the flare.
6 Form a 45-degree double flare on each end
Flare last, after bending and fitting, so both ends still carry slack and you do not come up short. Clamp the tube in the 3/16-inch slot of the flaring bar. Fit the matching adaptor and set the tube height to the base of the adaptor rather than to its nipple. First, drive the adaptor into the tube with the yoke to fold the mouth inward; then remove the adaptor and finish with the yoke alone to complete the second flare. In effect you crush the end twice, using the adaptor as a spacer on the first pass. Use a 45-degree tool, which is the automotive brake-line standard.
7 Mount the valve and connect the labeled lines
Secure the proportioning valve in its chosen location and connect each hard line to the port your earlier sketch assigned it, keeping every corner's circuit correct. Thread fittings by hand first to avoid cross-threading, then snug them with flare-nut wrenches; open-end wrenches or pliers will round the fittings and can ruin them. Route and secure the lines so they cannot chafe, vibrate against sharp edges, or contact hot components.
8 Bleed the system and check for leaks
Refill with fresh brake fluid and bleed every corner until firm, working the newly relocated valve into the sequence. Inspect every new flare and fitting for weeping under pressure, then confirm a solid pedal. Test braking at low speed in a safe area before any normal driving, and re-inspect the connections afterward.
Pro Tips
- 💡 The proportioning valve responds only to hydraulic pressure, so mounting angle and height are irrelevant; relocate it wherever convenient, which is common when a turbo setup crowds the stock spot.
- 💡 Bend one line at a time and lean on the factory line as a pattern; 12-gauge wire or earl's-style mock pieces make length and radius easier to nail.
- 💡 Reuse the factory 10mm metric nuts and save the short fractional nuts that came on the line for possible later use.
- 💡 A broom handle clamped in a vise gives good leverage for tighter bends when a cheap bender falls short.
- 💡 Flare only after all bending and fitting is done so each end keeps enough slack.
- 💡 Cut slowly for a clean, round cut and clear any swarf before flaring.
Was this guide helpful?