Brake Lines - Complete Set

Complete replacement of all hydraulic brake lines from master cylinder to all four wheel calipers, including bleeding and system verification.

Warnings

Tools required

Parts

• Complete brake line set (front to rear, master to ABS module) × 1 — Use OEM specification or pre-bent line kit for 2023 Bolt EUV
• Brake line clips and retainers × 1 — Replace all damaged clips
• Line fittings and sealing washers × 1 — Included with line set or purchase separately

Fluids

• ACDelco DOT 4 Brake Fluid — 2 qt

Preparation

1. Verify all replacement brake lines are correct length and have proper fittings installed
2. Ensure vehicle is on level ground before lifting
3. Disable 12V electrical system: open hood, disconnect negative terminal of 12V auxiliary battery (located in rear cargo area under floor panel)
4. Raise vehicle on lift or quality jack stands at all four corners, ensuring stability
5. Remove all four wheels and set aside
6. Place drain pans under work areas to catch brake fluid
7. Photograph or diagram entire brake line routing from master cylinder through ABS module to all four corners
8. Spray all line fittings with penetrating oil and allow 15-20 minutes to soak
9. Gather all tools, parts, and at least 2 quarts of fresh DOT 4 brake fluid within easy reach

Procedure

1. 1

   Drain brake fluid from system
   Open bleeder screws at all four calipers (rear wheels first, then front) and allow fluid to drain into collection pans. Use a line wrench to crack open fittings at master cylinder to allow complete drainage. Do not allow fluid to contact suspension components or paint. Once drained, close all bleeder screws finger-tight.
   Torque spec

   Bleeder Screw10 Nm (7 lb-ft)
2. 2

   Remove rear brake lines
   Starting at the rear calipers, use line wrenches to disconnect brake lines at caliper connections. Work toward the front, disconnecting lines at ABS module and along frame rails. Remove all mounting clips and brackets securing lines to frame and suspension. Label each line with its position (LR, RR) for reference. Inspect routing carefully before complete removal.
   ⚠Use only line wrenches (flare nut wrenches) on brake fittings. Standard open-end wrenches will round off the soft brass fittings.
   Torque spec

   Line Fittings20 Nm (15 lb-ft)
3. 3

   Remove front brake lines
   Disconnect front brake lines from calipers using line wrenches. Trace lines back to ABS module and master cylinder, removing all clips and brackets. The front lines typically route through inner fender area and along subframe. Note any grommets or protective sleeves at body penetration points. Remove lines completely and set aside.
   Torque spec

   Line Fittings20 Nm (15 lb-ft)
4. 4

   Remove master cylinder to ABS module lines
   Locate the brake lines connecting master cylinder reservoir to ABS hydraulic control unit (typically mounted near front of engine bay). Use line wrench to carefully disconnect both ends. These are critical lines—inspect replacement parts to ensure exact match before proceeding. Clean all connection points at master cylinder and ABS module with wire brush.
   ⚠ABS module contains electronics sensitive to brake fluid contamination. Cover module ports immediately after line removal with clean shop towels or plugs.
   Torque spec

   Line Fittings20 Nm (15 lb-ft)
5. 5

   Inspect and clean all mounting points
   With all old lines removed, inspect frame rail mounting points, clips, and brackets for corrosion or damage. Clean all threaded fittings at calipers, ABS module, and master cylinder with wire brush. Verify all bracket bolts are secure. Replace any damaged clips or retainers. Blow out any debris from mounting holes with compressed air.
   Torque spec

   Bracket Bolts102 Nm (75 lb-ft)
6. 6

   Install master cylinder to ABS module lines
   Begin installation with the lines connecting master cylinder to ABS module. Thread fittings by hand first to ensure proper engagement and avoid cross-threading. Once hand-tight, use line wrench to tighten to specification. Ensure lines are routed without kinks or sharp bends. Install any protective grommets or sleeves.
   ⚠Never use pipe thread sealant or Teflon tape on brake line fittings. Lines seal via flare or compression fitting only.
   Torque spec

   Line Fittings20 Nm (15 lb-ft)
7. 7

   Install front brake lines
   Route new front brake lines following exact path documented in preparation photos. Start at ABS module and work toward calipers. Install all clips and brackets in original positions, ensuring lines cannot contact moving suspension components or steering linkage. Leave caliper end connections hand-tight until routing is verified. Once routing is confirmed, torque all fittings with line wrench.
   Torque spec

   Line Fittings20 Nm (15 lb-ft)

   Bracket Bolts102 Nm (75 lb-ft)
8. 8

   Install rear brake lines
   Route rear brake lines from ABS module along frame rails to rear calipers, matching original routing exactly. Pay special attention to avoid contact with exhaust shields, suspension travel paths, and sharp edges. Install all mounting clips and verify at least 1 inch clearance from all moving components through full suspension travel. Torque all line fittings at connections.
   Torque spec

   Line Fittings20 Nm (15 lb-ft)

   Bracket Bolts102 Nm (75 lb-ft)
9. 9

   Verify line routing and clearances
   With all lines installed, manually cycle suspension through full travel at each corner (compress and extend) while checking for any line contact with components. Turn steering wheel full lock to lock and verify no interference with front brake lines. Check all mounting clips are secure and lines are properly supported every 12-18 inches. Adjust routing as needed before proceeding.
   ⚠️Lines that contact suspension or steering components will wear through and cause catastrophic brake failure. Verify clearances carefully.
10. 10

    Fill brake fluid reservoir
    Locate brake fluid reservoir at master cylinder. Fill with fresh DOT 4 brake fluid to MAX line. Keep reservoir covered when not actively filling to prevent moisture contamination. Have additional fluid ready for bleeding process. Do not reuse old brake fluid under any circumstances.
    ⚠Use only ACDelco DOT 4 brake fluid. Do not mix fluid types or use DOT 3 or DOT 5.1 as substitutes.
11. 11

    Perform initial manual brake bleeding
    Starting with the wheel furthest from master cylinder (typically RR, then LR, then RF, then LF), attach clear hose to bleeder screw and submerge end in clean brake fluid in container. Have assistant slowly press brake pedal to floor and hold. Open bleeder screw, allow fluid and air to escape, close bleeder screw, then release pedal. Repeat until fluid flows clear with no air bubbles (typically 5-10 pumps per wheel). Check reservoir level frequently and maintain above MIN line.
    ⚠Never allow reservoir to run dry during bleeding or air will enter ABS module requiring scan tool to purge.
    Torque spec

    Bleeder Screw10 Nm (7 lb-ft)
12. 12

    Perform ABS module bleeding procedure
    Connect scan tool capable of ABS bleeding function or use vacuum bleeder at each wheel. Follow scan tool prompts to cycle ABS solenoid valves while bleeding each wheel. This is ESSENTIAL on the Bolt EUV as ABS module contains trapped air that manual bleeding cannot remove. Cycle each valve 3-5 times per manufacturer procedure. If scan tool unavailable, use vacuum pump method: apply 30 seconds of vacuum at each bleeder while assistant cycles ignition on and presses brake pedal rapidly 15-20 times.
    ⚠️Skipping ABS bleed procedure will result in soft pedal and reduced braking effectiveness. ABS module bleeding is NOT optional on this vehicle.
    Torque spec

    Bleeder Screw10 Nm (7 lb-ft)
13. 13

    Final bleeding and torque verification
    Repeat manual bleeding sequence one final time at all four wheels in RR-LR-RF-LF order. Torque all bleeder screws to specification—do NOT overtighten as threads strip easily. Top off brake fluid reservoir to MAX line. Pump brake pedal 20-30 times—pedal should become firm and hold steady pressure. If pedal remains soft, repeat bleeding procedures.
    ⚠️Bleeder screws are brass and strip easily. Use precise torque wrench—overtightening will crack housing requiring caliper replacement.
    Torque spec

    Bleeder Screw10 Nm (7 lb-ft)
14. 14

    Reinstall wheels and perform final checks
    Clean wheel mounting surfaces on hubs. Reinstall all four wheels, threading lug nuts by hand first. Torque lug nuts in star pattern to specification. Lower vehicle to ground. Reconnect 12V auxiliary battery negative terminal. With vehicle still in PARK/neutral and on level ground, press brake pedal firmly—it should be hard and high. Start vehicle electrical system (do not energize drive system yet) and verify no brake warning lights on dash.
    ⚠Do not test drive vehicle yet. Static and low-speed verification must be completed first.
    Torque spec

    Wheel Lug Nuts140 Nm (103 lb-ft)

Reassembly

1. Verify brake fluid level is at MAX line in reservoir
2. Inspect ground under vehicle for any brake fluid leaks at all connection points
3. Verify all brake line mounting clips and brackets are secure
4. Confirm no brake warning lights illuminated on instrument cluster
5. Document brake line replacement in vehicle service records with date and mileage

Verification

• With vehicle stationary and engine/drive system OFF, pump brake pedal 30 times. Pedal should be firm and high (at least 2 inches from floor at full pressure). If pedal is soft or sinks, repeat bleeding procedures immediately.
• With vehicle stationary and drive system energized, apply firm brake pressure for 60 seconds. Pedal should not sink or require pumping. Any pedal movement indicates air in system or leak.
• Have assistant apply firm brake pressure while you inspect every brake line connection, fitting, and bleeder screw for any fluid seepage. Even small leaks will cause system failure.
• Perform low-speed test in safe area: drive vehicle forward at 5 mph and apply brakes firmly. Vehicle should stop straight with no pull and pedal should remain firm. Do NOT exceed 5 mph until next step is complete.
• Perform 10-15 brake applications from 15-20 mph in safe area to bed lines and verify system operation. Check for any unusual pedal feel, pulling, or warning lights. Pedal should remain consistent.
• Return to shop and re-inspect all fittings and connections for leaks after test drive. Check brake fluid level—any significant drop indicates leak.
• Perform final full-stop test from 30 mph in safe area only after all previous checks pass. Vehicle should stop straight with firm pedal and no ABS activation on dry pavement.
• If ANY of the above checks fail, do NOT drive vehicle. Re-bleed system or inspect for leaks/damaged components immediately.
• Re-check all line fittings and bleeder screw torques after 50-100 miles of driving and monitor brake fluid level weekly for first month.

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