expanded, or flared section at the end of the line. The flare
fits firmly against a seat, forming a leak-proof connection.
To connect to other hydraulic units, many steel brake
lines use double-lap flares at all connecting points. The
double-lap flare will withstand vibration and high pres-
sures. Notice in Figure 9-23A the flare angle is 45° while
the angle of the seat is 44°. This is called an interference
angle. When the nut is tightened into the fitting, the inter-
ference angle causes the seat and the flare to wedge
together. This wedging effect provides an effective seal
Another type of flare used for brake line connections
is the ISO flare. ISO stands for International Standards
Organization, a group that sets standards for international
trade and manufacturing. Similar to the double-lap flare,
the ISO flare provides a secure crack-resistant joint. An
ISO flare is shown in Figure 9-23B. Note that both flares
use a threaded nut, called a flare-nut, to hold the flare
against its seat.
Since the wheel brake units are independently sus-
pended (they can move in relation to the frame and body),
hydraulic connections between the wheels and body can-
not be rigid. Flexible hoses, Figure 9-24, are used at the
wheels to allow for movement. As the wheels rise, fall, and
turn, the flexible hose will transmit high pressure without
breaking. Most flexible hose lines are made from natural
rubber and synthetic fabric. There are usually two-plies
(layers) of rubber and two-plies of braided fabric material
for added pressure resistance. The hose is usually covered
by a synthetic rubber sheath to reduce damage from
atmospheric pollutants. See Figure 9-25. Some flexible
brake hoses use braided steel mesh between the rubber
layers for added strength. Braided mesh may also be used
over the outside of the hose to protect it from road debris.
Hose fittings are threaded to accept the flared tubing
of steel brake lines. The flexible hoses are firmly mounted
at each end, and all movement occurs in the hose itself.
Brake fittings are the threaded connectors that form
the junctions or connections in the brake hydraulic system.
Brake fittings are usually made of steel, but may also be
made of brass. Fittings can be as simple as the flare nut at
the end of a brake line, or as complex as a distribution
block that splits a single hydraulic line into numerous sep-
arate lines. Brake fittings such as distribution blocks and
tees are frequently solidly mounted on the frame or axle.
Some common brake fittings are shown in Figure 9-26.
160 Auto Brakes
Figure 9-23. A—A cutaway view of a double-lap tubing flare,
O flare nut, and the tubing seat. B—A cutaway view of an ISO
(International Standards Organization) type tubing flare.
(Niehoff) (Ni h ff)
Flare nut ISO flare Tube seat
44° Tube seat
Figure 9-24. A front suspension which uses a flexible rubberr
brake hose.The hose will allow the suspension to travel up and
down. A steel line would flex a few times, then break off, caus-
ing a loss of braking pressure to that wheel and eventual loss
of fluid to that portion of the hydraulic circuit. (Chevrolet)
e Brake ho se
Figure 9-25. A sectioned view of a flexible rubber brake hose.
Study the construction. (Wagner)) S d h i (W
Second ply First ply