There are a few reasons why you might want to swap your Civic's rigid, steel hydraulic clutch line for something else: It's difficult to get the OEM line and fitting assembly to cooperate with certain engine swaps, if you're going for that shaved-bay look then an ugly steel line running across the firewall simply won't cut it, and even if you're not going for that shaved-bay look a bit of steel braided bling is enough to spice up just about any engine bay. Although going overboard with the bling is never a good thing, the most important thing to keep in mind when working with hydraulic clutch and brake systems is the pressure involved. A typical automotive hydraulic clutch or brake line exhibits upwards of 1,500 psi internally. As the clutch or brake pedal is depressed, fluid pressurizes within the system causing the line to squirm around on its own. Imagine a garden hose that flings around by itself once the water is turned on-the principle is similar.
Flexible, steel braided lines are exactly that-flexible. As such, eliminating too much of the OEM rigid line or selecting too large of a line can result in a soggy pedal and/or poor braking or clutch engagement. An ideal clutch or braking system consists entirely of rigid line but that's simply impossible because of engine vibration and suspension travel. This is where flexible rubber or steel braided lines come into play. Use them sparingly though-like Honda did. A hydraulic clutch or brake system constructed entirely of steel braided hose isn't always the best idea.
As far as Civics go, only '92 and newer models feature hydraulic clutch systems, which makes this process somewhat useless for those with anything older. A typical '92-'95 Civic hydraulic clutch system consists of the ugly rigid steel line, dirty rubber hose, and metal brackets on the right. The steel braided setup on the left is much simpler and just looks better.
The OEM rigid line travels from the clutch master cylinder to the slave cylinder, located on the transmission. The line is intercepted by a short section of high-pressure rubber hose to allow for engine movement. Use a 10mm line wrench to remove the fitting from the clutch slave cylinder and then a 10mm socket to remove the two bolts holding the bracket in place. Set a drain pan underneath the vehicle to catch the residual fluid from the line and allow it to drain thoroughly before moving forward.
92-'95 Civics feature this aluminum clutch line connector located on the firewall directly behind the throttle body. You can either thread a 12x1.0mm to -3 adapter into the connector's left side and run steel braided line from here to the slave cylinder or you can remove this connector altogether and tap directly into the master cylinder. Keep in mind that the more flexible line you add, the greater the chance the clutch pedal may exhibit a soft feel, although this is generally more common with brake systems.
Running a line from the master cylinder to the slave cylinder requires just a few parts: approximately 60 inches of -3, Teflon-lined steel braided line, two 10x1.0mm to -3 inverted flare fittings, two appropriately sized hose clamps, and two -3 steel hose ends-a 180-degree one and a 45- or 30-degree one. Straight hose ends are cheaper and will work, but when working with steel braided plumbing it's best to achieve your bends by means of the fitting not the hose.
Use a 10mm line wrench to remove the fitting from the clutch master cylinder's outlet port and remove the line. Carefully unclip the clutch line from the brake lines along the firewall and remove any brackets connecting it to the chassis using a 10mm socket. Brake fluid is an excellent paint remover so be sure and wrap the line's ends with a rag before pulling it out.
Thread the adapter fitting into the clutch master cylinder's outlet port. Do not use any type of sealant here-that's what the inverted flare is for. Applying Teflon tape or sealant will cause a leak. Assemble both hose ends onto the hose before connecting it to the -3 fitting. Connect the 180-degree end to the clutch master cylinder end, turning it in such a way so as to allow clearance between the tube and the firewall. The hose should route underneath the brake booster and along the firewall.
Use a suitably sized hose clamp to attach the line to the firewall where the factory aluminum connector was. Don't be lazy or cheap here. The line will flex and move every time you step on the clutch if you skimp on clamps.
This clamp is even more important because it will prevent the line from shorting out against the starter's main power wire. Find a suitable location on the transmission or framerail and clamp the line down. This B-series transmission bracket works well.
Thread the remaining fitting and hose end onto the clutch slave cylinder. Be sure to orient the hose the way you want it before making the final turn. Again, stay away from that sealant.
Of course, you'll need to bleed the clutch system of air bubbles since it's been opened. Use a 8mm line wrench to crack open the bleeder fitting and purge away.