Brake Line - Single

Replace a single damaged or corroded brake line on a 1970 AMC Rebel Machine, restoring brake hydraulic integrity to one wheel circuit.

Warnings

Tools required

Parts

• Brake line tubing (3/16" or 1/4" steel, depending on location) × 1 — Use OEM specification copper-nickel or steel brake line
• Brake line fittings (inverted flare type) × 2 — Match original fitting size and thread pitch
• Brake line mounting clips × 1 — As needed for routing

Fluids

• DOT 3 or DOT 4 brake fluid — 1 qt

Preparation

1. Park vehicle on level ground and set parking brake firmly. Place wheel chocks behind wheels that will remain on ground.
2. Identify which brake line requires replacement by tracing from master cylinder to wheel cylinders or calipers, looking for corrosion, damage, or leaks.
3. Purchase correct diameter brake line tubing (typically 3/16" for wheel lines, 1/4" for main lines on 1970 AMC) and matching fittings with proper thread pitch.
4. Raise vehicle at appropriate jacking points and support securely on jack stands. Remove wheel if replacing a line to front or rear brake assembly.
5. Place drain pan under work area to catch brake fluid spillage.
6. Apply penetrating oil to brake line fittings at both ends of damaged line and allow to soak for 10-15 minutes if corrosion is present.

Procedure

1. 1

   Relieve brake line pressure and open master cylinder
   Remove the master cylinder reservoir cap to prevent vacuum formation when disconnecting lines. Do not depress brake pedal during this procedure or air will be drawn into the system.
2. 2

   Disconnect brake line at master cylinder or junction block end
   Using appropriate flare nut wrench (typically 7/16" or 1/2" for AMC applications), carefully loosen the brake line fitting at the upstream connection (closest to master cylinder). Hold the mating component steady with a backup wrench if needed to prevent twisting the block. Allow brake fluid to drain into pan. Once loosened, unthread fitting by hand to avoid cross-threading.
   ⚠Use only flare nut wrenches (six-point box wrenches with slot) to prevent rounding off the soft brass fittings. Standard open-end wrenches will damage fittings.
3. 3

   Disconnect brake line at wheel cylinder or caliper end
   Move to the downstream end of the damaged line (at wheel cylinder, caliper, or intermediate junction). Use flare nut wrench to loosen fitting. On rear drum brake wheel cylinders, the fitting is typically 3/8" and accessed from behind the backing plate. Support the wheel cylinder or caliper body with backup wrench to prevent twisting the component.
4. 4

   Remove line mounting clips and extract old line
   Locate all mounting clips or brackets securing the brake line to the frame, axle housing, or body. Remove clips by prying tab, removing retaining bolt, or bending open as appropriate for clip type. Carefully route the old line out, noting the exact path, bends, and clearances from exhaust, suspension, and drivetrain components. Take photos or make sketches for reference.
5. 5

   Measure and cut new brake line
   Measure the old line length or measure the routing path with string or wire. Add approximately 3-4 inches for bending allowance. Cut new brake line tubing to length using a tubing cutter (preferred) or hacksaw. If using hacksaw, ensure cut is perfectly square and deburr inside and outside edges with reamer or file to prevent restriction and allow proper flare formation.
6. 6

   Create double flares on both ends of new line
   Using a double-flaring tool, create proper SAE double (inverted) flares on both ends of the new brake line. Insert tubing into flaring tool at correct depth per tool instructions (typically one tubing diameter beyond bar face). Tighten clamp securely. Form initial flare, then complete double flare per tool design. Inspect flares for cracks, splits, or irregularities; reject and re-cut if imperfect.
   ⚠️Improper flares will leak under pressure and cause brake failure. Flares must be smooth, concentric, and without cracks. If uncertain about flare quality, practice on scrap tubing first.
7. 7

   Bend new line to match original routing
   Using a tube bender or careful hand bending over rounded surface (never kink the line), form bends in the new line to match the original routing. Bends should be smooth and gradual with radius of at least 3 times the tubing diameter. Test-fit the line along the route, ensuring it does not contact exhaust, sharp edges, or moving suspension/drivetrain components. Maintain at least 1/2 inch clearance from hot or moving parts.
8. 8

   Install fittings and position new line
   Thread the appropriate brake line fittings (nuts) onto each end of the new line before installation. Route the new line through mounting clips and along the predetermined path. Ensure the line follows the original routing and maintains proper clearances. Loosely install mounting clips to hold line in position but allow minor adjustment.
9. 9

   Connect line at wheel cylinder or caliper end first
   Start the downstream fitting (at wheel cylinder or caliper) by hand, threading carefully to ensure proper engagement without cross-threading. Once hand-tight, use flare nut wrench to snug the connection. Do not fully tighten yet; leave slightly loose to allow alignment adjustment when connecting the other end.
10. 10

    Connect line at master cylinder or junction block end
    Start the upstream fitting by hand, ensuring threads engage smoothly. Adjust line position and routing as needed to allow fitting to thread without forcing or bending the line. Once hand-tight, use flare nut wrench to tighten while holding mating component with backup wrench. Tighten firmly but do not over-torque (typically 10-12 ft-lbs for brake fittings, but use judgment as no spec provided).
11. 11

    Final tighten all connections and secure mounting clips
    Return to the wheel cylinder/caliper end and final tighten that fitting with flare nut wrench. Verify both connections are secure without over-tightening which can damage flares. Tighten all mounting clips, ensuring line is secure but not stressed or strained at fittings. Verify clearances to all components remain adequate.
12. 12

    Bleed brake system at affected wheel
    Fill master cylinder reservoir with fresh DOT 3 or DOT 4 brake fluid to MAX line. Attach clear bleeding tube to bleeder screw at wheel cylinder or caliper on the affected circuit. Submerge other end of tube in clean brake fluid in container. Have assistant slowly depress brake pedal while you open bleeder screw 1/2 to 3/4 turn. Close bleeder before pedal reaches floor. Repeat until fluid flows with no air bubbles. Keep master cylinder filled throughout process.
    ⚠️Never allow master cylinder to run dry during bleeding or air will enter the system requiring complete system bleeding. Check reservoir level after every 3-4 pedal strokes.
13. 13

    Bleed remaining wheels if necessary
    On the single-circuit system in the 1970 Rebel, air may have migrated to other wheels. Bleed in sequence: right rear, left rear, right front, left front (farthest from master cylinder to nearest). Use same procedure as Step 12 for each wheel until all air is purged from entire system.

Reassembly

1. Reinstall wheel and torque lug nuts to proper specification (typically 75-80 ft-lbs for 1970 AMC, but verify with owner's manual).
2. Remove jack stands and lower vehicle to ground.
3. Fill master cylinder reservoir to MAX line with fresh brake fluid and install cap securely.
4. Pump brake pedal slowly 10-15 times, then hold firm pressure. Pedal should feel firm and high. If pedal is soft or sinks, air remains in system; re-bleed affected circuits.
5. Inspect all connections for leaks while assistant holds firm pedal pressure. Look for fluid seepage at both line fittings.

Verification

• With engine off, pump brake pedal several times and hold firm pressure for 30 seconds. Pedal must remain firm and high without sinking. Any pedal sink indicates air in system or leaking connection.
• Start engine (if power brakes equipped, though 1970 Rebel Machine typically had manual brakes) and verify pedal height remains adequate and firm.
• Perform low-speed test in safe area: at 5-10 mph, apply brakes firmly. Vehicle should stop straight without pulling. Verify no leaks visible at any connection point after test.
• Road test at progressively higher speeds in safe area with no traffic, verifying normal brake operation and no warning light activation.
• After initial test drive, re-inspect all connections for leaks and verify brake fluid level has not dropped in master cylinder reservoir. Top off if needed.
• Re-check brake line routing after test drive to ensure no contact with moving or hot components occurred during suspension/drivetrain movement.

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