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Brake Line Tech

Posted in How To on August 1, 2009
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You're jamming across the dirt about to carve a tight turn through a sandy berm or you're puttering through a busy school zone on the way to pick up your kid. These two scenarios would seem to have little in common, but we'd bet in both cases you're counting heavily on your brakes to do their job reliably. Speed and power is great, but when it's time to haul your vehicle back down to slow you'll want some dependable stopping power, and part of that system relies on your brake lines. After the addition of go-fast parts, the grand smile on your face will quickly turn to an expression of panic should you be missing the vital braking power needed to bring your vehicle back to a halt in a safe manner.

Factory stock brake lines (the flexible portions) are commonly made from rubber hose and have a long history of reliability under normal driving conditions on the road. In contrast, stainless braid lines consist of a Teflon inner tube surrounded by other protective layers, one of them being braided stainless mesh hose. The Teflon tube offers several advantages. It does not expand with pressure, is unaffected by high temperature, is compatible with all types of brake fluid, and resists deterioration with age. However, the Teflon is fairly fragile to outside contact with debris or rubbing on nearby surfaces. This is where the stainless braid and other protective layers come into play to encase the Teflon.

Whenever you lift your rig or you're building something custom, you may be in need of longer brake lines. Sometimes it's possible that a longer rubber line with the same style connectors is available from another OEM application to meet your custom need. However, most times, an aftermarket stainless braid line is the answer.

For off-road applications, the stainless lines offer the benefit of increased puncture protection when compared to a rubber line. In a situation where the line may encounter trail brush or flying rock and dirt, a stainless braid line will survive such abrasion better than a rubber line will. A side benefit to the stainless braid is that it helps support the Teflon tubing so that it doesn't swell under pressure like a rubber line, and can provide a firmer pedal action. This becomes even more helpful with lifts where hose length is added and would normally contribute to greater hose bulge.

Hose Connectors
All brake hoses are terminated with either threaded connector ends or banjo style ends to mate to another fitting or hardline, or to a brake caliper. There are two basic means by which the end connectors are secured and sealed to the hose. The first method essentially crimps the connector to the hose with a metal ring. The second method uses a two-part assembly where the hose is captured between an inside and outside fitting that are screwed together. The latter style is a type that can be done without sophisticated crimping machinery using bulk hose and fittings. However, this type of line is sometimes used on race vehicles and is not approved for highway use.

Are Stainless Lines D.O.T. Approved?
Indulge us a bit here and we'll explain. Flexible brake lines on road vehicles are governed by Federal Motor Vehicle Safety Standard 106 which specifies the construction and test requirements for hydraulic hose assemblies. Department of Transportation (D.O.T.) approved hoses can only use a fixed crimped or swaged end fitting. Secondly, an approved hose must meet a `whip' test where the hose is flexed back and forth while pressurized to determine if the hose and fitting combination can withstand repeated movement without failure. Some stainless brake lines have failed this criteria due to hose failure where the hose enters the hard metal fitting.

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Here is another example of a hose marked as D.O.T. approved. This one has no external vinyl coating but does use a rubberized support over the area where the hose mates to the fitting.

How Do Lines Differ?
The better quality hoses to look for are those that offer several protective layers over the Teflon inner core to provide both mechanical strength to the hose and to keep dirt and abrasives out of the layers. With all the time and cash you have tied up into building your vehicle it just doesn't make sense to skimp on brake line quality by using a poor quality part with so much at stake.

We spoke with Tom Kirastoulis of Crown Performance Products about how a company typically tests a manufactured hose. Crown builds and tests each of their lines onsite in their facility in Vista, California. The hoses are hydrostatically pressure tested to 4500 psi using water to simulate and surpass expected brake fluid pressure in the vehicle application.

Maintenance & Inspection
Rubber brake hoses can be inspected for scars, nicks, bulging and soft spots on a regular basis and replaced as needed. However, one characteristic of a stainless braid line is that the Teflon hose inside does not deteriorate and bulge over time, so visual signs of impending failure are harder to see. In any case, all brake lines should be inspected periodically for problems that could lead to failure. Lines should always have sufficient slack to prevent any undue tension on them during any steering or suspension travel movement. Also check to ensure they cannot become caught on any part on the rig and be torn or stressed.

One way a stainless line can degrade is if dirt works its way into the line such that it contacts the Teflon tubing and is allowed to abrade on this surface. Over time, the Teflon tubing may rupture and cause a fluid leak. Most stainless lines have some type of plastic or vinyl sheathing over them to prevent this hazard.

Sticking With Stock
OEM rubber brake lines are typically very reliable (when not externally damaged). Despite the planned obsolescence of most hoses found on vehicles these days, the rubber brake lines are high on the safety list and will often last the life of the vehicle. They are constructed from layers of fabric impregnated with rubber, then wrapped in a tough sheath of rubber or plastic material.

Despite their longevity, it's a good idea to periodically inspect the hoses for cracks, chafing, bulging or other distortion, and fluid leaks. On a 4WD vehicle you are typically flexing the suspension and chassis quite a bit and traversing trails where you'll encounter brush, rocks and other road hazards that could damage the lines.

On Brake Fluid
Hydraulic fluid used in automotive brake systems is called upon to provide an incompressible medium with a constant viscosity, withstand heat and cold, lubricate internal components, and prevent corrosion.

4WD vehicles typically use DOT 3 or 4 grades of brake fluid. Grade 2 is an obsolete type meant for older drum brakes and Grade 5 is silicone brake fluid and is not compatible with Grades 3 and 4. The higher the grade number, the higher the boiling point of the fluid, which translates to higher performance capability.

When adding fluid to your brake system it is best to use new fluid from a sealed container. Brake fluid is hygroscopic, meaning it has the ability to absorb moisture. Water held within the fluid lowers its boiling point. When heated during braking, the moisture can boil. This results in vapor formation in the calipers or wheel cylinders and can lead to a spongy pedal or brake failure. A 3- to 4-percent moisture content can drop the boiling point by about 100 degrees. A fluid flush and replacement every couple of years is a good preventative measure.

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