This procedure covers the complete removal and replacement of the brake master cylinder on a 2014 Ram 2500 with 6.7L Cummins diesel engine, including brake line disconnection, master cylinder installation, and complete brake system bleeding.

Warnings

Tools required

Parts

• Brake master cylinder assembly × 1 — Use OEM Mopar specification for 4WD diesel model
• Master cylinder cap and diaphragm (if not included) × 1 — Verify included with master cylinder

Fluids

• Mopar DOT 4 Brake Fluid — 2 qt

Preparation

1. Park vehicle on level surface and set parking brake securely
2. Chock rear wheels to prevent vehicle movement
3. Open hood and locate brake master cylinder on driver side firewall/booster assembly
4. Place fluid catch pan and towels around master cylinder work area to protect paint and catch spills
5. Using turkey baster or evacuator, remove as much old brake fluid from reservoir as possible to minimize spillage
6. Have new DOT 4 brake fluid ready but keep containers sealed until needed
7. Ensure you have an assistant available for brake bleeding procedure or have pressure bleeder ready

Procedure

1. 1

   Disconnect electrical connector
   Locate the brake fluid level sensor connector on the master cylinder reservoir. Press the locking tab and disconnect the electrical connector. Move the wiring harness aside to prevent damage during removal.
2. 2

   Remove brake line fittings from master cylinder
   Using the appropriate flare nut wrench, carefully loosen and remove the brake line fittings from the master cylinder ports. There are typically two lines: primary and secondary circuits. Hold the master cylinder body steady while loosening to prevent damage to internal components. Allow brake fluid to drain into catch pan. Cap or plug the open brake lines immediately to prevent contamination and further fluid loss.
   ⚠Use only flare nut wrenches to prevent rounding off brake line fittings. Standard open-end wrenches will damage the soft brass fittings.
   Torque spec

   Brake Line Fittings15 Nm (11 lb-ft)
3. 3

   Remove master cylinder mounting nuts
   Locate the two mounting nuts securing the master cylinder to the brake booster. These are accessed from inside the engine bay. Using a socket and ratchet, remove both nuts evenly. Note the position of any spacers or washers for reinstallation.
   ℹ️Some models may have either 25 Nm or 27 Nm specification - verify with your specific service manual which applies to your build date.
   Torque spec

   Master Cylinder Nuts25 Nm (18 lb-ft)
4. 4

   Remove master cylinder from brake booster
   Carefully pull the master cylinder straight off the brake booster studs. The pushrod from the booster will disengage from the master cylinder piston. Keep the master cylinder level to minimize additional fluid spillage. Have shop towels ready to catch residual fluid. Inspect the brake booster pushrod for damage or corrosion.
5. 5

   Inspect and prepare new master cylinder
   Remove the new master cylinder from packaging. Verify it matches the old unit in mounting configuration and port locations. Check that the reservoir is empty or contains only shipping fluid (which must be removed). Inspect the mounting face and internal bore for any shipping damage or contamination.
6. 6

   Bench bleed new master cylinder
   CRITICAL STEP: Bench bleeding removes air from the master cylinder before installation. Secure the master cylinder in a vise with soft jaws. Install short lengths of clear hose on both outlet ports, routing the hoses back into the reservoir. Fill reservoir with fresh DOT 4 brake fluid to MAX line. Using a smooth wooden dowel or Phillips screwdriver, slowly press the master cylinder piston inward 1 inch, then release. Repeat this process 15-20 times until no air bubbles emerge from the return hoses. Keep reservoir filled throughout. Remove hoses and immediately cap ports until installation.
   ⚠Failure to properly bench bleed the master cylinder will make system bleeding extremely difficult and may result in a soft brake pedal.
7. 7

   Install master cylinder to brake booster
   Carefully align the new master cylinder with the brake booster studs, ensuring the pushrod properly engages with the master cylinder piston. The master cylinder should slide onto the studs smoothly without binding. Install both mounting nuts finger tight, then torque evenly in a cross pattern to specification. Do not overtorque as this can damage the booster or master cylinder.
   Torque spec

   Master Cylinder Nuts25 Nm (18 lb-ft)
8. 8

   Connect brake lines to master cylinder
   Remove caps from brake lines and master cylinder ports. Thread each brake line fitting by hand to ensure proper thread engagement and prevent cross-threading. Once hand-tight, use the flare nut wrench to tighten to specification. Connect the primary circuit line first (front brakes), then secondary circuit (rear brakes). Ensure lines are properly routed without kinks or interference.
   ⚠Cross-threading brake line fittings will ruin the master cylinder ports. Always start threads by hand and ensure smooth rotation before using tools.
   Torque spec

   Brake Line Fittings15 Nm (11 lb-ft)
9. 9

   Reconnect electrical connector and fill reservoir
   Reconnect the brake fluid level sensor electrical connector until it clicks into place. Fill the master cylinder reservoir with fresh DOT 4 brake fluid to the MAX line. Install the reservoir cap hand tight (approximately 4 Nm). Do not overfill.
10. 10

    Bleed brake system - Master cylinder
    Begin bleeding at the master cylinder. With an assistant, have them slowly pump the brake pedal 5-6 times and hold down. Slightly crack open one brake line fitting at the master cylinder to release air, then immediately tighten. Repeat this process for each line until no air bubbles emerge and only clear fluid flows. Maintain reservoir level above MIN throughout bleeding process.
    ⚠Never allow reservoir to run dry during bleeding or air will re-enter the system requiring complete restart of bleeding procedure.
11. 11

    Bleed brake system - All four wheels
    Bleed brakes in this order: Right Rear, Left Rear, Right Front, Left Front (furthest from master cylinder to closest). At each wheel, locate the bleeder screw on the brake caliper. Attach clear hose to bleeder screw and submerge other end in brake fluid in catch bottle. Have assistant pump brake pedal 3-4 times and hold down. Open bleeder screw 1/2 turn, allow fluid and air to escape until pedal reaches floor, then close bleeder. Repeat until no air bubbles appear and only clean fluid flows. Tighten bleeder screw to specification after final bleed at each wheel. Check and refill reservoir after each wheel.
    ⚠️Brake pedal must be held down when opening bleeder screw to prevent air being drawn back into the system. Release pedal only after bleeder is closed.
12. 12

    Verify brake pedal firmness
    With engine off, pump brake pedal several times. Pedal should become progressively firmer and hold firm pressure. If pedal is soft or spongy, repeat bleeding procedure starting at master cylinder. With engine running (vacuum assist active), pedal should drop slightly when first pressed, then remain firm. There should be no pedal fade when held under constant pressure for 30 seconds.
    ⚠️A soft or spongy pedal indicates air remains in the system. DO NOT drive the vehicle until pedal is firm and brakes are verified functional.

Reassembly

1. Verify all brake line fittings are tightened to specification and show no signs of leakage
2. Fill master cylinder reservoir to MAX line with fresh DOT 4 brake fluid and ensure cap is properly installed
3. Verify brake fluid level sensor connector is fully seated and locked
4. Clean any spilled brake fluid from painted surfaces immediately with water
5. Dispose of old brake fluid and contaminated rags according to local environmental regulations

Verification

• With engine off, pump brake pedal multiple times - it should become firm within 3-4 pumps and maintain pressure
• Start engine and verify pedal drops slightly when first pressed, then remains firm with no fade
• Check for fluid leaks at master cylinder mounting area and all brake line connections
• Verify brake fluid level is at MAX line and brake warning light is off on instrument cluster
• Perform initial test in safe area: Test brakes at low speed (5-10 mph) to verify proper operation and firm pedal feel
• Gradually test braking at increasing speeds up to 25 mph in safe area before returning to normal driving
• During first 50 miles, periodically check brake pedal feel and inspect for leaks around master cylinder
• Re-check brake fluid level after first drive cycle and top off if needed - some settling is normal

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