Flushing The Brake Hydraulic System; Brake Pipes And Hoses - GMC G Service Manual

FLUSHING THE BRAKE
HYDRAULIC SYSTEM
It is recommended that the entire hydraulic system be
thoroughly flushed with clean brake fluid whenever new
parts are installed in the hydraulic system.
Flushing is also recommended if there is any doubt as to
the grade of fluid in the system or if fluid has been used
which contains the slightest trace of mineral oil. Flush the
system whenever there is any question of contamination.
Flushing is performed at each bleeder valve in the same
manner as the bleeding operation, except that the bleeder
valve is opened 1 1/2 turns and the fluicUs forced through
the lines and bleeder valves until it emerges clear in color.
Refer to "Bleeding the Brake Hydraulic System" in this
section.
Check master cylinder fluid level after flushing at each
valve and replenish if required. When flushing is completed
at all bleeder valves, make certain the master cylinder res­
ervoir is filled to the proper level.

BRAKE PIPES AND HOSES

The hydraulic brake system components are intercon­
nected by special steel piping and flexible hoses. Flexible
hoses are used between the frame and the front calipers,
and the frame and rear axle. When the hydraulic pipes have
been disconnected for any reason, the brake system must
be bled after reconnecting the pipe. Refer to "Bleeding the
Brake Hydraulic System" in this section.
FLEXIBLE HOSE
On the front brakes the hose is connected to the caliper
with a bolt and copper washers. The fitting at the other end
of the hose is secured at the frame with either a nut or a
clip.
At the rear axle, one end of the hose is connected to the
axle with a bolt; the other end is secured at the frame with
either a nut or a clip.
Flexible Hose Inspection
The flexible hoses should be inspected for any signs of
road damage which will cause cracks and chafing of the
outer cover. If any of these conditions are visible, replace
the hose.
Hose Replacement
M Remove or Disconnect (Figure 4)
• Clean dirt, grease, and other foreign material from the
hose fittings at both ends.
1. Steel pipe.
2. Clip or nut (31).
3. Bolt (34).
4. Washers (33).
5. Hose bracket nut (60).
6. Hose (32).
HYDRAULIC BRAKES 5A-7
M Install or Connect (Figure 4)
• Use new copper washers when installing the hose.
1. Hose (32).
• The hose must not be twisted.
] Important
• The hose installation must not contact any sus­
pension components.
2. Hose bracket nut (60).
3. Washers (33).
4. Bolt (34).
5. Clip or nut (31).
6. Steel pipe.
• Bleed the brakes. Refer to "Bleeding the Brake
Hydraulic System" in this section.
BRAKE PIPES
When replacing a steel brake pipe, always use steel
piping which is designed to withstand high pressure and
resist corrosion. The same size pipe must be used as the
one removed.
NOTICE: Never use copper tubing for hydraulic
brake lines because copper is subject to fatigue
cracking and corrosion, which could result in
brake failure.
Brake pipes that run parallel to each other must main­
tain a 6mm (1/4-inch) clearance.
Pipe Flaring (Figures 5 and 6)
Tools Required:
J 23530 Flaring Tool or equivalent
In order to ensure a proper flare, flaring tool J 23530 or
equivalent must be used (figure 6). When using the tool,
instructions furnished by the tool manufacturer should be
followed. Always inspect newly formed flares for cracks or
malformations which might cause leaks. After flaring, blow
out the brake pipe with compressed air before installing it
on the vehicle.
NOTICE: A double-lap flaring tool must be used,
as single flaring tools cannot produce a flare
strong enough to hold the necessary pressure.
1. Use steel pipe and fittings of the correct size. The
outside diameter of the pipe is used to specify the
size.
2. Cut the pipe to length. Add 3mm (1/8-inch) to the
length for each flare.
3. Flare the pipe ends by following the instructions with
the tool.
4. Bend the pipe to match the old pipe using a pipe
bender.