Mopar 4721154AA Brake Master Cylinder

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To remove the master cylinder, start by pumping the brake pedal with the engine off to relieve the vacuum inside the power brake booster, preventing contaminants from entering it. Remove the battery and use a syringe to siphon the brake fluid from the master cylinder reservoir. Place rags under the fluid fittings and prepare to cap or bag the line ends when disconnected. Loosen the line fittings with a flare-nut wrench, move the lines slightly, and quickly plug the ends. Thoroughly clean the mounting area, remove the nuts attaching the master cylinder to the power booster, and carefully pull it off. If necessary, transfer roll pins from the old reservoir to the new master cylinder, ensuring new seals are installed between the master cylinder and reservoir.

Bench bleeding the master cylinder is important to expedite the bleeding of the entire hydraulic system after installation. To bench bleed, insert threaded plugs into the cylinder outlet holes, fill both reservoirs with brake fluid, and support the master cylinder level to prevent spillage. Loosen and tighten one plug at a time while pushing the piston assembly into the bore to expel air, preventing its return. Alternatively, you can remove the plug, depress the piston, and use your finger to seal the hole to prevent air from re-entering. Repeat this for both ports, stroking the piston three or four times for each outlet to ensure complete air removal. Refill the master cylinder reservoirs and install the cover assembly, being mindful not to overfill them.

To install the new master cylinder, bench bleed it first by mounting it in a vise and attaching bleeder tubes to the outlet ports. Fill the reservoir with recommended brake fluid and slowly push the pistons into the master cylinder to expel air into the reservoir, preventing air from being drawn back in. Remove the bleed tubes, install plugs, and the reservoir cap. Put a new vacuum seal on the master cylinder where it mates with the power booster. Install the master cylinder over the power brake booster studs and finger-tighten the nuts. Thread the brake line fittings into the master cylinder, ensuring they don't strip. Fully tighten the mounting nuts and brake line fittings. Fill the reservoir with fluid, then bleed the master cylinder and brake system with an assistant. Loosen the fittings, allowing air and fluid to escape, and repeat this on both fittings until the fluid is clear of air bubbles. Use rags to catch spilled brake fluid to avoid damaging painted surfaces. After bleeding, rinse the area under the master cylinder with clean water. Finally, test the brake system's operation carefully before normal vehicle use.