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Fabricating, Bending, Flaring & Installing Custom Hard Lines for Brakes, Oil, Fuel, Coolant & Turbo

Fabricating, Bending, Flaring & Installing Custom Hard Lines for Brakes, Oil, Fuel, Coolant & Turbo

There are always certain elements to car maintenance and modification that intimidate the average 4wd enthusiast. Examples of this include stuff like paint, bodywork, electronics and plumbing brake and fuel systems. Body work and paint are definately forms of art and should probably be left to someone who does it every day. Simple electronic work can be done by the enthusiast but more complex work can take some figuring out. When it comes to plumbing hard lines forbrakes and fuel - like many other aspects of working on cars, it can take some special tools, but running lines is truely a job anyone can do.

In fact, running hard lines can be a very enjoyable job.  There's something satisfying about taking a piece of straight hardline and making bends in it to take it through the route it needs to go.  All it takes is the right tools and some practise and you'll be able to run professional looking hard lines through your vehicle.

The ability to repair and replace hard lines can come very handy in bush and outback situations where you may find yourself with a hard line puncture under your 4wd vehicle or worse if your brakes suddenly become unusable.  Other situations where you may be wanting to modify your 4wd by adding turbochargers, bigger brakes or aftermarket cooling to your vehicle might require the use of custom hard lines in your vehicle.

Tools Required

We recommend you get a hold of the following tools before attempting to run your own hard lines in your vehicle:

  1. Hard Line Bending Tool
  2. Tube Cutter
  3. Flare or Double Flare Tool (depending on the job)
  4. Flare Nut Wrench (variety of sizes)

Hard Line Flare

Two types of flares are commonly used on hardlines.  A 37 degree flare and a 45 degree double flare.

37 degree flares are commonly referred to as AN (Army/Navy) or JIC flares.  These flares are used with aircraft style fittings and have never been used on a production vehicle.  They are often used in fuel lines for race cars and hotrods.  This is often the way braided steel soft lines are incorporated into a custom vehicle.  These fittings have become more popular with custom vehicle builders as the availability of aluminium annodised fittings and tube has increased.

Double Flare 45 degree flares are used in most automotive hard line since the 1930's.  They are a doubled over flare end that is most commonly found on brake line hard lines.

Creating a flared hard line:

  1. Cutting of tube should be done with a proper tube cutter tool.  Failing this a hacksaw can be used.  Careful squaring and preparation of the end of the tube should be done with a belt sander and debur tool.
  2. The tubing is then inserted into the flare tool to create the flare.  Make sure to remember to put your brake line fitting or tube nut and sleeve (in a 37 degree flare) before you flare the end!
  3. If you are using mild steel brake tubing the tube must be double flared with a two step process.  A die is used to flare the tube once, then remove the die and re-flare with the cone shape tool to fold the metal back on itself.  Using a double flare helps prevent mild steel tube cracking.
  4. AN or JIC flares require only a single flare tool.  The cone shaped tool is used advanced into the mouth of the tube to create the single flare.
  5. It is important to mate 45 degree flares to 45 degree fittings and 37 to 37.  Attempting to mate 37 to 45 degree flares will often end in leaks as there is a much smaller sealing surface and is not recommended.

Hard Line Fittings

Fuel and brake line fittings are made of brass which is a lot softer than steel.  Flare nut wrenches are specifically made to grip as much of the fitting as possible.  When removing a brake line fitting always use a flare nut wrench.  Open ended tools will marr and round off the fitting causing a lot of headaches.

Using Teflon Tape

Never use teflon tape to seal any type of flared fitting for automotive use.  The flared end of the tube seats against the brass insert in most components.  This is what creates the seal.  As you tighten the fitting, the flared end is pressed tighter against the fitting.

Teflon tape should only be used in tapered thread situations such as pipe threads.  Any flared fitting that is leaking, is not leaking past the threads.  It's leaking through between the flare and the fitting itself.  To stop the leak, attempt to loosen the fitting and reseat the flared end.  If the leak does not go away, the seat in the fitting is damaged or you may need to reflare the hard line.

It's also important that you don't over-tighten the fittings. Simply snugging them up will cause the fittings to seat together. Over-tightening won't stop a leak.

How to Bend Hard Lines

Bending brake lines and other hard lines has to be approached with caution.  If you are aggressive with your bending, you can potentially kink the line and waste your tube.  A tube bender is the best tool for this job.  Find one with a tight radius suitable for the size of tube you're working with.

At a pinch, it has been suggested to fill the tube with fine sand and bend it around a socket however this will never be as consistent as a proper tube bender.