Thin tubes push high-pressure fluid to four corners of your vehicle. With this, a modern hydraulic braking system hauls your rig down to a firm stop. Or, so you hope. In our world, big tires and heavier, upgraded wheels mean we’re rolling more inertia on our axles, and we can tax the stock brake components heavily. Getting big tires up to speed can sometimes be a chore, but stopping straight, quick, and smooth can be just as challenging.
These days, high-quality aftermarket pads and rotors provide more stopping power, which helps turn that rolling energy into heat. But another point of upgrade lies in the factory rubber brake hoses, and we don’t want these to be a weak link. One downside of rubber lines is they swell slightly under hard braking, eating up a little bit of your braking efficiency and giving a slight reduction in braking feel.
When installing a lift, it’s often a great time to upgrade your brake hoses. In some cases, it’s possible to add an additional OEM hose to add length or use a longer OEM hose from another application, but you’re compounding the hose swell issue when you do this. A swap to stainless brake lines at this point is a wise to achieve the added length you need and maintain a firm pedal feel.
Quality stainless braided brake lines also offer improved strength over rubber hoses. They are constructed from a Teflon inner tube covered with other protective layers, including a braided stainless mesh hose. The Teflon tube doesn’t expand with pressure, is unaffected by brake fluid or temperature, and has little deterioration with age. It’s a relatively fragile structure alone, hence, the need for the covering layers to protect from abrasion and debris that could come in contact with it.
Today, it’s easier to find aftermarket stainless hoses that are Department of Transportation (DOT) approved for use on public highways. These hose types have passed a ‘whip’ test, which ensures they can reliably withstand repeated flexing movement without failure. DOT-approved hoses are also required to use a fixed crimped or swaged end fitting on the hoses.
We dropped by Crown Performance Products (crownperformance.com) in Vista, California, to get a lesson on stainless braid brake lines like the ones we commonly use when building or modifying our off-road rigs. Crown President Tom Kirastoulis showed us how DOT-approved brake lines suitable for highway and off-road use are assembled in his manufacturing facility.
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1. Factory rubber lines with metal fittings are economical for the vehicle manufacturer and provide decent performance in stock applications. They’re generally designed to last the life of the vehicle under reasonable driving and weather conditions. Off-roaders use their vehicles under more stress and harsher conditions, so many times stainless brake lines are a valuable upgrade.
2. The factory brake lines were designed to work within the limits of the factory suspension. When lift or extra travel is added, always check for sufficient brake line length and unencumbered movement. If a hose is pulled tight under full suspension movement, you may eventually fatigue and tear the line open or off. Many times, a longer stainless brake line is the best answer to accommodate the movement and upgrade the brake system.
3. The brake hose used consists of a multi-layer stack with a Teflon inner core followed by a Kevlar braided sheath, a protective layer, the stainless steel braid, and finally, an outer vinyl cover that is added during final assembly of individual brake lines. Teflon Inner Core Kevlar Braid Protective Layer Stainless Steel Braid D.O.T. Tag & Color Vinyl Cover
4. Bulk hose is cut to the desired length using a sharp shear. The blade can cleanly cut through all the hose layers leaving the ends ready to accept connectors.
5. The appropriate end is pressed into the hose with a moving fixture, as the hose is held crimped in an alignment jig. Brake line manufacturers must source a wide variety of metal connector ends to mate with OEM and custom applications.
6. Crown adds an outer vinyl covering over each stainless braid line. Dirt that works its way into the stainless mesh can start to abrade the more delicate Teflon tubing inside, and eventually, cause a leak. The vinyl is just another protection for the inner tube.
7. With the metal connectors pressed into the hose, the brake line moves to a hydraulic crimping tool, where an eight-jaw metal die crimps the connector shell onto the hose in one fluid motion. This is the critical joint of the hose and a proper crimp is needed for a long-lasting and leak-free line.
8. Crown has an air table equipped with various fittings to mate to any of their brake lines. Each line they build is individually pressure tested to 4,000psi.
9. As a final step, each line is visually inspected an additional time, then packed with any related hardware that might go in the brake line kit. Stainless braid brake lines are available with a wide range of connection options. Stock replacement kits are typically available for popular applications, and custom hoses can be fabricated to meet special needs or to mate to swapped-in brake components.
10. Given high quality stainless lines don’t suffer from the same hose bulge problems as rubber lines, it’s possible to use them in greater lengths without an issue. We’ve used the braided line to plumb fully across the length of a straight axle, and plenty of buggy builders and racers have plumbed entire rigs with stainless braided lines.
11. When clearance near the brake connections are tight, it’s often possible to get custom brake lines with 90-degree steel fittings. These can also be helpful when you’re using stainless braid lines running from your master cylinder.
12. Stainless brake lines will last a long time, but should be checked periodically as with all brake lines. Our rigs see flying dirt and rocks, brush, and other hard obstacles under our chassis and axles. A rubber hose may start to bulge before failure, but a stainless line typically will not display such signs as readily. Check for kinks and nicks in the outer cover or braid, any hose deformation, and signs of stretching or abrasion.
13. If you have any worry about longer brake lines flopping around, and you don’t have a place to secure them, use this simple method. A piece of rubber hose was wrapped around the line and a steel spring used to keep the hose in position while still allowing it to stretch the spring and move as the axle droops.
14. Whenever you’re working on brake lines, it’s a good idea to use a flare nut wrench on the fittings. This allows you to get a solid grab on the connector and tighten it sufficiently without marring the hex on the fitting. Open-end wrenches tend to flex more and can damage the fitting hex.
15. Brake fluid is hydroscopic. In other words, it absorbs water from the atmosphere. Once this happens, the boiling point of your brake fluid drops. As little as 3 to 4 percent water content can drop the fluid boiling point by about 100 degrees. Consider flushing and changing your brake fluid periodically with fresh fluid from a sealed bottle. This becomes even more important if you live in a high-humidity climate.