June 2014 Issue

Them's the Breaks: Brake (and Other) Line Repairs

Even if you work where road salt isn't used, that doesn't mean brake and other metal line repair shouldn't be in your repair repertoire. Road debris and other hazards also damage lines on a regular basis.

The earliest chariots, carts and wagons featured quite rudimentary brakes, if they used any at all. The earliest known brake consisted of a stout wooden stick inserted parallel to the axle through a hole near the rim of a solid wooden wheel and extending under the chariot platform. This parking brake could not be deployed on the move, of course, but was sufficient to keep your horse from wandering off with your cart. Archaeologists say that later Roman chariots employed a chain brake attached to a cross tree ahead of the wheel and looped under the axle hub. The charioteer pulled the chain upward with greater or lesser force to modulate his braking power. By the 1800s, lever-operated wooden brake shoes were in widespread use. These shoes usually acted directly on the iron-clad rim of the wheel.

About a hundred years ago, the great Italian race car designer Ettore Bugatti, whose cars had dominated European auto racing for years, held out against the newfangled hydraulic brakes for his cars, relying instead on elegantly designed mechanical brakes with numerous rods and pivots. Asked why, he famously replied, “I build my cars to go, not to stop!”

As we all know, modern cars are now universally equipped with hydraulic brakes, though some may feature layers of additional technologies grafted on top. The principles on which they operate were laid out by the famous 17th century French philosopher and scientist Blaise Pascal, whose hydraulic press amplified or multiplied a smaller force acting on a smaller area into the application of a larger force totaled over a larger area, transmitted through the same pressure (or same change of pressure) at both locations. This same principle is embodied in the design of all hydraulic braking systems to this day.

One of the most important implications of the principle of hydraulics is that any change in pressure applied at any point of the fluid is transmitted undiminished throughout the fluid. Thus, like a chain, a hydraulic circuit is only as strong as its weakest point.

Here in the Salt Belt of the upper Midwest, that “weakest point” tends to show up a lot, usually around 8 to 12 years after the vehicle was built. The symptoms are a low brake pedal, increased stopping distance and an illuminated red BRAKE warning light. This may also be accompanied by an illuminated ABS and/or VSC warning light.

Until the pedal sank, you might easily have overlooked the underlying salt-induced corrosion. As is often the case, the salt accumulated on top of the line bracket where it could easily be missed. Over a period of years, it oxidized the steel line, causing the eventual perforation and leak. Because oxidation is accelerated by heat, most of the actual rusting took place during the warmer months of summer, although the salt was certainly deposited there during the winter driving season. My observation is that regular underbody washing can delay this type of damage by many years (see “An Ounce of Prevention,” on page 22).

Of course, brake lines are not the only victims of this indiscriminate killer. Fuel, power steering, oil cooler and transmission cooler lines are also often affected, as are rear heater and a/c tubes. I’m going to concentrate primarily on brake lines, but will touch on the rest in passing.

Before you replace the damaged brake line, you’ll want to know whether or not you can get the caliper and wheel cylinder bleeder valves open. And since this can have a big impact on the total bill, your customer will need to know this, too. If things have already progressed to the point of an actual leak, you have little to lose in trying to open those bleeders early on. Get your customer’s authorization, and get to work!

The Challenge

You probably already have a brake line flaring kit, and have used it more than once. But if you’re a typical tech, you’re probably missing at least one important step that can make the difference between a good flare that seals perfectly and a bad one that either leaks or requires so much torque that it damages the threads of the fitting (see “Machine-Assisted Flaring,” on page 30).

Photo 2 above shows a double-flared replacement brake line being made. Technician Joe Sandow has already used a tubing cutter to make a clean cut perpendicular to the line. He’s used a reamer to remove the “flash” from the center of the cut. Here, he’s chamfering the circumference prior to clamping the line in a tubing vise. Chamfering prevents the tubing from splitting during the forming process. It’s more critical with harder alloy lines, and slightly less critical with more ductile alloys.

Photo 3 on page 24 shows the line being positioned in the clamp. Make sure you slide the fitting on first, facing the right way, of course. Use the countersunk side of your tubing vise for double-flared lines. Align the lower edge of the chamfer with the shoulder on the die. Put a drop or two of brake fluid on the stem and face of the die to lubricate it properly. Crank down on the forcing screw until it stops. It’s not necessary to bend the handle! Remove the die, put another drop or two of brake fluid on the cone, then crank it down until it stops. Again, don’t bend the handle.

Mark Lauretig of Gene’s Marathon in Cleveland Heights, OH, told me that it was easy to “overflare” the thinner-walled (.019-in.) Ni-Copp alloy tubing. Especially when making a traditional double-flare, cranking down too far on the forming cone can leave you with an unsealable flare that will leak no matter how much you torque the fittings. His suggestion is to stop forming the second flare cone about a half-turn before you normally would. This allows the tightening of the fitting to finish up the final flare and provides good conformity between the line flare and its mate. Subsequent experiments showed him to be correct, although I was unable to duplicate the overflare problem with the thicker-walled (.028-in.) SUR&R tubing I normally use.

The Mastercool’s hydraulic pressure required its own solution to the overflare problem. Analogous to the manual flare tool solution, the trick was to learn to stop pumping the tool’s hydraulic cylinder just when it first began to offer firm resistance. Continuing until a mechanical stop was achieved became a prescription for failure.

Photo 6 on page 27 reminds us to position the fitting close to the new flare before beginning to bend the line into its final configuration. While the fitting can pass over a slight angle, it can easily become trapped on the wrong side of a sharp bend. Speaking of bends, it’s critical that they be done right. There are a variety of tubing benders and specialty pliers available to help you avoid problems. Kinks in the wall of a hydraulic line can reduce flow or even cause residual pressurization. Low flow becomes a functional problem in poorly adjusted brakes, where substantial quantities of fluid are required to move a wheel cylinder or caliper piston sufficiently for effective braking. Residual pressurization can cause dragging brakes, and can cause decreased fuel economy and/or increased brake fluid temperature, potentially resulting in a loss of braking if the fluid boils or vaporizes from the heat. (Vapors are compressible, after all.) In the interest of thoroughness, I should mention that a small amount of residual line pressure is sometimes engineered in for drum brake applications to prevent air from being sucked in past the wheel-cylinder seal cups when the brakes are released.

These days, the availability of easily bendable alloy tubing makes it practical to flare both ends of even a very long front-to-rear brake line off the car in a single piece. Measure the original line length using a piece of string. Cut your new line and flare on the fittings. A bit of masking tape will both cover the open ends of the line and hold the fittings close to where you’ll want them. The new line can be fitted into place by following alongside the original. You can even support it against its predecessor if you plan to leave the original on the car.

Sometimes you may wind up with a fairly sharp bend in the middle of your replacement line after you send one end forward up the firewall by the steering gear and the other end rearward up and around the fuel tank. This is when you’ll be very glad to already have a pair of brake line straightening pliers to smooth things out. Obviously, avoiding kinks is equally important when repairing cooler lines as well.

If you need to make a bend but don’t have a bender with the correct radius, you can use a socket, an old bearing race, starter armature housing or anything of the right general dimensions as a mandrel. Just be sure not to kink the tubing. Using a section of closely fitting wire-wound spring over the tubing in the area to be bent helps prevent kinking. You’ll often see such sections in factory-formed lines.

In a pinch, I’ve even been known to put a block-off end plug onto my flared fitting, then fill a transmission cooler line with ATF, plug the other end and bend it around an anvil horn to achieve the right shape. (If your supplier doesn’t have a block-off, get a couple of unions and line nuts. Flare a short section, crimp it over in a vise, attach it to the union and presto! You have a block-off.) Because the fluid is incompressible, forming it with the line full (similar to “hydroforming” frame members) prevents unwanted kinks and ensures good flow. Nickel-copper alloy tubing is readily bendable, but not all alloy lines are created equal; thinner walled tubing kinks much more readily.

Typical torque specs for a flared fitting on a 3⁄16-in. (4.75mm) line are approximately 11 ft.-lbs. (15Nm). This is not a significantly high torque, and the fitting materials are often brass, substantially softer than the steel we usually work with. Along with oil drain plugs and wheel lugnuts, these are among the most commonly overtightened fasteners in the repair industry. Still, as 30+ year veteran technician Joe Sandow wisely puts it, “Real world? The right torque spec is enough that it won’t leak.”

Material Selection

Let’s start at the beginning: Regular copper tubing is forbidden. Not only does it lack the requisite burst pressure, it tends to “work-harden” when exposed to vibration. This paradoxically renders it more brittle as it ages. Most OEMs use steel alloy lines, although several high-end marques, such as Jaguar, Volvo and Porsche, feature a .028-in. walled nickel-copper alloy essentially identical to that supplied by SUR&R and some other suppliers. Only flared fittings are approved for brake line use.

Your fittings must match one another at each junction. You cannot use a double-flare fitting in a bubble-flare caliper, cylinder or union, although there are adapters available to get you from one type to the other safely. The pressure seal in a brake line is always metal-to-metal. Therefore, thread sealant is neither required nor allowed. The job of the threads is merely to clamp the tube into its corresponding fitting with sufficient force to prevent leakage under even the most extreme internal pressure.

Compression fittings are quick and relatively easy to install on fuel lines and oil or transmission cooler lines, but it’s illegal to use them on brake lines. Why? The short answer: They may fail, just when you need them the most. Here’s the skinny: In a flared-union fitting, the threads’ clamping force is exerted onto the shoulder of the flared line. This shoulder matches the fitting’s main diameter in such a way that the line cannot pull through the fitting nut. The flared tubing end itself complements a companion shape in the other fitting. (For automotive brake applications, the female flare is at a 45° angle.) The two should self-center on assembly, with the seal being made by the tube’s end being forced strongly against the companion fitting.

In contrast, the clamping force from the threads of a compression union is exerted on a movable sleeve or ferrule which, in turn, pinches or compresses onto the line. Since the line’s outside diameter is no larger than the inside diameter of the fitting nut, there’s no fail-safe to prevent separation. Even the use of “double-ferrule” fittings does not meet FMVSS requirements for brake lines. Thread sealants such as joint compound (pipe dope or thread seal tape such as PTFE tape) are unnecessary on compression fitting threads, as it’s not the thread that seals the joint but rather the compression of the ferrule between the nut and pipe.

It’s critical to avoid overtightening the nut; if you do, the ferrule will deform improperly, causing the joint to fail. Paradoxically, overtightening is the most common cause of leaks in compression fittings, but they can (and do!) also fail because of excessive vibration or internal fluid pressure.

Best practice for automotive compression union applications such as transmission cooler lines is to use vibration-resistant fittings. High-temperature fittings with fluoroelastomer sleeves are rated for temperatures from 215° to 450°F, while Buna-N or equivalent rubber sleeves provide a working range between 230° and 275°F, certainly adequate for most nonbrake applications in temperate zones.

Depending on size and design details, compression fittings are rated for maximum pressures of 150 to 1200 psi. This is well below the required pressure rating for hydraulic brake lines and fittings, which are engineered to withstand working pressures of up to 3000 psi, with burst strength rated at approximately 17,000 psi. Brake flex hoses are required to have a burst strength of at least 5000 to 7000 psi, depending on diameter, and are typically designed for working pressures of 1900 psi or more.

Bleeding

Air is compressible, hydraulic fluid is not. We need to make sure that there’s no air in our newly repaired brake lines. There are several ways to accomplish this.

Traditional bleeding requires a helper to depress the brake pedal on command. The sequence in a typical shop involves pumping the pedal repeatedly, then holding it down. The farthest bleeder valve is then opened, allowing air and/or fluid to escape. The valve is then closed before the pedal is released. At this point, there should be no further pumping of the pedal; single strokes should suffice. This process is then repeated until no further air is observed when the valve is opened.

The fluid level in the master cylinder reservoir must be monitored and replenished as needed. The bleeding process is then repeated for each of the remaining hydraulic circuits in turn. At the end, each should be rechecked a final time to make sure that no previous aeration has occurred. Some ABS-, collision avoidance system (CAS)- or brake assist system (BAS)-equipped vehicles may require additional scan tool-based procedures as well. Check the manual for the specific model you’re servicing.

An alternate procedure utilizes a hand-operated or compressed air-driven vacuum pump attached to the bleeder valve by a tight-fitting (preferably transparent) hose with a fluid supply bottle attached to the master cylinder to prevent the system from running dry. (A light coating of brake assembly fluid on the bleeder threads will seal it effectively.) An alternative style applies pressure to the reservoir. The bleeders are then opened until only clear fluid emerges.

One of my favorite techniques is reverse bleeding. Using a high-volume syringe (no needle!) attached to the bleeder valve via a clear plastic tube, fluid is introduced into the line under light pressure. This fills the line from the business end back to the reservoir. The process ends when no more bubbles appear in the reservoir. (Tip: Start with a very low fluid level in the reservoir; you’ll fill it as you go.) This technique works extremely well with clutch hydraulics, too.

While brake lines are subjected to much higher working pressures, many fuel injection systems can run at 70 psi or more, so fuel leaks, especially from a pinhole puncture, can send a stream of gasoline several feet, possibly onto a hot exhaust. The good news is that semirigid nylon tubing can usually be substituted for damaged steel lines, cutting labor time significantly.

A number of special tools are available, including some to insert quick-connects or barbed splice couplings into these lines. In most cases, using a dedicated repair kit provides more easily installed options to meet your repair needs, including fittings designed to be used with an Oetiker-style ring clamp fastener like that on most CV boots, and compression unions specifically designed to join steel lines to nylon lines. One additional favorite is an in-line fuel check valve to combat hot-restart woes when the original unit integral to the pump assembly has failed.

My area has seen a dramatic increase in rodent-related damage in recent years, possibly due to a string of milder-than-normal winters, although this last one, with its “polar vortex,” was anything but. Some of this rodent damage has been in the form of gnawed pinholes in factory-installed nylon lines. It turns out these sections are usually easily repaired once you gain access to the area of the leak using one of the commercially available kits mentioned.

We’ll leave you with a few tips to carry you through an uneventful brake line service:

•Specialized bending and straightening pliers can make your brake job much easier.

•Don’t crimp off brake flex hoses unless you’re replacing them anyway. Crimp-off pliers can cause damage to the inner wall, resulting in eventual failure, including residual pressure faults. Many complaints of brake pull have been traceable to internal damage resulting from this practice.

•Brake flex hoses cannot be substituted for rigid lines; by their nature they flex, resulting in a slight drop in effective brake pressure. Using flex lines longer than those originally specified can result in a very spongy brake pedal and poor braking performance. Stainless-wrapped hoses flex slightly less, and result in a firmer pedal feel.

•Actual brake pressure readings may vary from vehicle model to model. Dedicated testing equipment is available.

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