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When it comes to running fluids from one end of a chassis to the other, one of the safest, simplest and most sanitary methods is to use hard lines. With the fluctuating quality of fuel being produced and the unknown compatibility of certain fuel additives with the various rubber compounds being produced today, it's also a safer bet when it comes to a consistent method of delivery that won't break down over time. Not only will a solid length of metal tubing not leak over time so long as it isn't damaged, a hardline will also provides a higher level of protection from said damage over rubber hard lines or similar. Hard lines are also less susceptible to heat and abrasion issues as they can be run in a manner that results in zero movement and secured firmly using line clamps.
Hard lines are of course nothing new to the automotive world, but what is new is the variety of metal tubing now available in the aftermarket, particularly from Earl's Performance Plumbing. Stainless steel tubing, capable of being installed as-is or polished to a highly buffed finish is often the choice of the most discrete builders. But stainless can be expensive and difficult to work with, so Earl's offers a handful of affordable mild steel tube options that are soft enough to bend and flare using standard tools. And speaking of soft, Earl's also stocks annealed aluminum tubing in two sizes, 3/8- and 1/2-inch, which is super easy to work with.
With all these options, it might be difficult to decide which hard line is the best choice for your build. But fear not, we're going to walk you through the different options available and help you decide what fits your project best.
Stainless steel is a common material used in high end builds due to its strength and aversion to oxidation. It looks great right out of the box and can be further manipulated to look even better. The drawback of stainless however, aside from its expense, is that it can be difficult to work with, especially when it comes to creating a double-inverted 45-degree flare, as is standard in OE-style brake systems. For the most discerning tastes however, stainless is hard to beat.
A more affordable option to stainless is this zinc-plated steel hard line kit from Earl's. The bright zinc plating gives this line the look of more expensive polished stainless while providing great corrosion resistance. Earl's steel hardline is double-wall, low-carbon steel, copper brazed tubing and is available in sizes ranging from 3/16- to 3/8-inch, making it perfect for brake lines, transmission cooler lines, and fuel lines. Earl's offers steel hardline in 25-foot coils, or packaged as a kit with a variety of fittings and hoses, depending on the application.
Earl's Olive-coated steel hard line is similar in construction and workability to their zinc-plated offering, but with a Poly-Vinyl-Fluorine (PVF) coating that provides superior corrosion protection, making it ideal for vehicles that are exposed to harsh road conditions, such as snow, road salt, gravel, or coastal salt air environments. It is available in similar sizes and kit configurations as their Zinc-plated steel line.
One of the latest forms of hardline to hit the market, though it's been used on a number of OEM vehicles as far back as the '70s, is Earl's Easy-Form tubing. Manufactured from a copper-nickel alloy, Easy Form tubing is as strong as steel, but much easier to bend and flare. While this alloy is roughly 90% copper and 10% nickel, it should not be confused with typical copper tubing found at your local hardware store. Ideal for use on all automotive hardline systems, Easy-Form tubing (also commonly referred to as Ni-Cop) is available in sizes ranging from 3/16- 3/8-inch diameters, as a single-length roil of coiled tubing or complete with the appropriate fittings and hoses.
The last piece of tubing worth discussing is Earl's Annealed Aluminum tubing. Unlike Earl's steel and stainless steel tube offerings, aluminum tubing is not DOT approved for use in brake systems. Thus, diameters are limited to 3/8- and 1/2-inch only. Where annealed aluminum tubing shines however, is in its ability to be easily formed, bent, beaded, and flared. Adapters can be welded onto the ends of the tube, the tubing can be flared and used with AN tube nuts and sleeves, or the ends of the tube can be beaded and used with Earl's ECON-O-FIT hose ends or with standard hose clamps to transfer fuel, oil, or transmission fluid. Annealed aluminum tubing is not recommended for use in applications over 100 psi and never to be used in a brake system.
When it comes to automotive applications of hard line use, there are two basic types of flares utilized: 45-degree double inverted and 37-degree single flares. Double inverted flares (pictured here in 3/16-inch stainless) can be found in a variety of applications, including transmission, fuel, and brake fittings. The drawback to the double inverted flare is that they can be difficult to form perfectly in stainless.
AN or Army-Navy fittings are commonly found on high-end builds and racecars and are formed using a single 37-degree flare in the tubing, a tubing nut, and sleeve. Due to the single flare process, successfully flaring stainless tubing is much easier using the 37-degree method. This type of fitting is commonly used in any automotive fluid application, from a 3/16-inch stainless steel brake line to a 1/2-inch diameter aluminum fuel line. AN fittings are assigned using 1/16-inch increments and are specified by the diameter of the tubing. For example, 1/2-inch tubing uses AN-8 fittings (1/2 converted to 16th. equals 8/16). AN fittings have become industry standard in the automotive aftermarket as well as the racing world. Earl's carries a myriad of fittings, hose, and adapters to suit any build in AN componentry.
Earl's Professional Flaring Tool (p/n 001ERL) makes 37-degree, 45-degree, and DIN flares quickly in all types of tubing. This bench-mounted flaring tool makes it easy to flare stainless steel with professional results. In addition to the die-cast steel body, and quick-change die-clamp bolt/lock are fifteen dies and two turrets with sixteen punches. Capable of working with all materials, from NiCop to stainless, in diameters ranging from 3/16- to 1/2-inch 37-degree flares, 3/16- to 3/8-inch 45-degree flares (4.75, 6, 8, and 10mm as well) and 3/16- and 1/4-inch DIN flares.
When it comes to flaring tubing, there are a couple tips to help you get the best flare possible, every time. The first is to get as square a cut as possible by using a small diameter tubing cutter like Earl's part #003ERL.
For harder materials, like stainless steel, an abrasive chop saw can be used to avoid work hardening the tubing, which can make the flaring process more difficult and result in cracked flares.
Once the tubing is cut to length, it's a good idea to deburr the inside of the tubing.
The outside edge should be lightly dressed with a file to remove any burrs or imperfections that might prevent the flaring tool’s die from properly forming the tube.
Here's a section of 3/8-inch aluminum tubing that's been flared to 37-degrees and is ready to connect to a AN-6 male fitting. The tube nut and sleeve was installed before the tubing was flared.
Bending hard line tubing varies in difficulty depending upon the material being used. As mentioned, Earl's offers a number of different tubing from the easiest to bend (Easy Form, aluminum, etc) to much harder (stainless). No matter the material however, for the best results, all tubing should be bent using a properly sized tubing bender. Earl's offers a variety of benders with dies ranging from 3/16- to 1/2-inch, and capable of bending a variety of angles (from 90- to 180-degrees) in a variety of different centerline radii. Here, Earl's Professional Lever Style Tubing Bender (p/n 025ERL) is great for bending tight radii in 3/16-inch tubing.
Earl's Standard Tubing Bender is capable of bending 1/4-, 5/16-, and 3/8-inch tubing up to 180-degrees in a slightly larger radius.
When it comes to bending tubing, there are a few tricks that are worth mentioning. For starters, most bends are going to be marked corresponding to a particular chassis feature, etc that the tube needs to bend around. Marking the tube and transferring that to where to start the bend is unique to every bender. It's a good idea to make a couple test bends to see where your bender starts to make the bend.
Typically, one can mark the tube where the bend should begin and install the tube in the bender, lining up the mark with the dial marked out on the bender.
For example, for this particular bender, this results in a 90-degree bend that started at the mark.
We made another 90-degree bend on the same plane, this time with a larger radius bender. Note the difference between the two bends.
Oftentimes, it's necessary to make another bend on the same section of tubing, but on a different plane. This can become confusing, even for the most experienced fabricator. A quick trick is to mark the centerline of the tubing using a fine line marker.
Next, the tube is marked where the next bend will begin.
Our larger radius bender will again be used for our third bend. Note the centerline marking on our tubing aligns with the edge of the bender's die, while the mark for the beginning of the bend again aligns with the first hash mark on the bender's dial. This will ensure the next bend is on the proper plane when compared to the first.
The finished section of tubing shows the different plane bends as well as two finished flared ends with the proper tube nut and sleeves installed.