Which Brake Line Wrench Is Right for My Vehicle?

Brake line wrenches (often called flare nut wrenches or simply line wrenches) serve a specific purpose in a mechanic’s toolbox. Several styles exist, but determining which brake line wrench is right for my vehicle isn’t really that hard, but it’s imperative to get the correct tool.

“People frequently use standard wrenches and pliers to try working with brake line fittings, but this approach usually ends in rounded nuts,” says Alan Gelfand, owner of German Car Depot. “Using the correct tool from the beginning produces fewer complications than trying to force improper tools on brake line fittings.”

Brake line fittings on modern vehicles tend to use metric measurements between 8mm and 17mm, while American vehicles from older models use SAE sizes between 3/8″ and 5/8”. Line wrenches also typically have a different size on each end, so buying one wrench gives you two sizes.

Here’s what else to know about choosing and using brake line wrenches.

Why Do I Need a Special Brake Line Wrench?

Common wrenches that grip with a pinching action have the potential to crush the parts that comprise the joint in a hydraulic line. Hydraulic brake lines are held together in a special way that evenly distributes pressure around the circumference of the joint.

It begins with a widening of the line end called a flare. The flared end of the line slips over the seat to create an overlapped joint. Before creating the flare, the end of the line is run through a hollow nut called a flare nut. It then slides over the seated flare, gripping its lip and pulling it firmly against the seat as it’s threaded on to the fitting. The flare nut and fitting both have thin walls and so are susceptible to damage from wrenches that squeeze or pinch.

What Is Different About a Brake Line Wrench?

A standard box wrench cannot be used on a brake line because it has a closed end. An open-ended wrench may grip the nut, but often the line joint is located in tight places where the wrench does not swing far enough to allow a second placement with the nut in its new position.

Brake line wrenches, on the other hand, engage five of the six faces of the nut, allowing just enough of an opening to let the line slide through.

“Brake line fittings are tightly secured, and they are under the vehicle, subject to rust and salt,” says Chris “Moose” Pyle, an automotive expert with JustAnswer. “You cannot get a socket or boxed-in wrench on them, and an open-ended wrench with only two contact areas will often round off the fitting, versus a line wrench, which contacts the fitting on all sides but one.”

Also, the jaws of the wrench are wider than the typical combination wrench, to increase the surface area for contact. The increased contact area helps prevent the soft metal of the nuts and fittings from being rounded off by the wrench.

Which Type of Brake Line Wrench Is Right for My Vehicle?

The style of wrench you choose for your vehicle depends on how much room you have to operate.

Some resemble a combination wrench, with different sizes at each end. The Geardrive 10-piece Flare Nut Wrench Set is a straightforward option with more sizes than you need for brakes, making it a good choice if you’re looking to build out your tool collection for fuel line or HVAC projects.

Then there are Crowfoot-style wrenches, which require a socket drive for use. This Neiko Crowfoot Flare Wrench Set mounts on the 3/8-in. or 1/2-in. drives on socket wrench handles or torque wrenches, so you can assemble them in different ways. This may allow you to turn a nut positioned where a straight wrench can’t access it.

Ratcheting-style wrenches are perfect in tight spaces since they eliminate the need to disengage the wrench after every stroke. The E-Z Red 4-Piece Ratcheting Double Box Flare Nut Wrench Set, then, is a good choice for cramped brake line setups.

For durability, look for wrenches made from high-grade chrome vanadium steel or another quality alloy. A chrome finish helps prevent rust, allows greasy hands to grip better and is easier to clean up. Gelfand also recommends a 15-degree offset head for easier access.

“Low-cost wrenches tend to bend when used under pressure, increasing the chance of rounding the fittings,” he says. Also, “The way jaws are designed plays an essential role. Brake line wrenches with precisely machined jaws and smooth edges deliver the best results because they protect the fitting surfaces from damage.”

Adds Pyle, “A good tool is an extension of your hand, so buy good tools. They do not have to be the most expensive ones from a tool truck, but better than no-name stuff from Amazon.”

FAQ

What if the brake line nut is stuck or rounded?

First, try coating it with penetrating oil, then let it soak for at least 20 minutes. If that doesn’t work, some heat from a small propane torch might do the trick (for safety, be sure to keep it away from rubber parts and brake fluid).

If that fails, “Often, a pair of vice grips can get a stubborn fitting to release,” says Pyle. “If you have to do more drastic things, then you may need to cut the end of the line off and use a new fitting and a flare tool to add a new double flare to the tip of the brake line.”

Also, don’t try to force damaged brake lines through rounded fittings, as that can create costly problems, says Gelfand. To prevent future problems, apply a thin layer of anti-seize compound when reassembling the brake line connections.

Do I need a full set or just one wrench?

You might be able to get away with only one wrench, but it’s not a bad idea to buy a full set of brake line wrenches, since brake systems contain various sized fittings. “The serious DIYer who performs vehicle work should invest in quality brake line wrenches with metric and SAE options to protect their fittings and prevent costly complications,” says Gelfand.

About the Experts

• Alan Gelfand has been the owner of German Car Depot for more than 30 years. His business is an independent automotive service center in Hollywood, Florida, specializing in the service and repair of German vehicles.
• Chris “Moose” Pyle is a master-certified technician with 20-plus years of automotive experience, and an auto expert on JustAnswer, the expert on-demand platform.