Steel Brake Lines
Hydraulic brake lines are made of steel tubing, flared at both ends to accommodate male fittings. They are available in different lengths and diameters, the most common sizes being 3/16" (4.8 mm) 1/4" (6.4 mm), and 5/16" (7.9 mm) outside diameter, and can be bent to conform to the application.
Most lines are made of double-walled, welded steel tubing that is coated to resist rust. The ends are double flared or have an ISO-type flare to guard against leakage.
Before installing a double-flared brake line, place the tube nuts over the tubing. Any metal chips or dust particles should be removed before assembly.
The ends are flared using a special double flaring tool. The tube nut forces each flared tube end against a matching seat-making a high pressure seal. It is important to start the male fitting into the wheel cylinder or hose by fingers to prevent cross threading and thread stripping. Once started, tighten to manufacturer's specifications.
ISO flares-recommended by the International Standards Organization-has several advantages over conventional double flares:
- Tube seats are not needed.
- When tightened, the shoulder of the nut bottoms out in the body of the part, creating a uniform pressure on the tube flare.
- The design is not subject to overtightening. The technician merely tightens the nut firmly on the seat and the correct sealing pressure is obtained automatically.
A special tool is required to make ISO flares. This tool is designed for use in a bench vise and requires only one die to form the brake line flare.