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The system is sealed, so since the problem started before repairs, chances are it isn't air. Since there are no leaks and the reservoir stays full, my first suspect is the master cylinder. Take a look through this link and see if it mirrors what you are experiencing.
I suspect that is the issue. Here is a link that shows in general how one is replaced:
Here are the directions specific to your vehicle. The attached pictures correlate with the directions.
2005 Chrysler Pacifica V6-3.5L VIN 4
Vehicle Brakes and Traction Control Hydraulic System Brake Master Cylinder Service and Repair Procedures Master Cylinder
CAUTION: Vacuum in power brake booster must be pumped down (removed) before removing master cylinder from power brake booster. This is necessary to prevent power brake booster from sucking in any contamination as master cylinder is removed. This can be done simply by pumping brake pedal, with vehicle's engine not running, until a firm feeling brake pedal is achieved.
1) With engine not running, pump brake pedal until a firm pedal is achieved (4-5 strokes).
2) Disconnect negative battery cable from battery post and isolate.
3) Thoroughly clean all surfaces of brake fluid reservoir and master cylinder. Use only Mopar Brake Parts Cleaner or equivalent.
4) Disconnect wiring harness connector from brake fluid level switch in master cylinder brake fluid reservoir (Fig. 48).
5) Disconnect primary and secondary brake tubes from master cylinder (Fig. 49). Install sealing plugs in open brake tube outlet ports.
CAUTION: Before removing master cylinder from power brake vacuum booster, master cylinder and vacuum booster must be thoroughly cleaned. This must be done to prevent dirt particles from failing into power brake vacuum booster.
6) Clean area where master cylinder assembly attaches to power brake booster. Use only Mopar Brake Parts Cleaner or equivalent.
7) Remove two nuts attaching master cylinder to power brake booster (Fig. 49).
8) Slide master cylinder straight out of power brake booster.
CAUTION: Seal on rear of master cylinder is used to create seal for holding vacuum in power brake vacuum booster. Vacuum seal on master cylinder MUST be replaced whenever master cylinder is removed from power brake vacuum booster.
9) Remove vacuum seal located on mounting flange of master cylinder. Vacuum seal is removed from master cylinder by carefully pulling it off rear of master cylinder. Do not attempt to pry seal off master cylinder by inserting a sharp tool between seal and master cylinder casting.
1) Thoroughly bleed master cylinder before installing it on vehicle.
CAUTION: When replacing master cylinder on vehicle, a NEW vacuum seal MUST be installed on master cylinder.
2) Install NEW vacuum seal on rear of master cylinder making sure seal fits squarely in mounting groove.
3) Position master cylinder on studs of power brake booster (Fig. 49), aligning booster push rod with master cylinder piston.
4) Install two master cylinder mounting nuts (Fig. 49). Tighten both mounting nuts to a torque of 25 Nm (225 inch lbs.).
CAUTION: When tightening primary and secondary brake tube nuts at master cylinder, be sure brake tubes do not contact any other components within vehicle and that there is slack in flexible sections of tubes. This is required due to movement between ABS ICU and master cylinder while vehicle is in motion.
5) Thread primary and secondary brake tubes into master cylinder primary and secondary ports (Fig. 49). Brake tubes must be held securely when tightened to control orientation of flex section. Tighten tube nuts to 14 Nm (120 inch lbs.) torque.
6) Connect wiring harness connector to brake fluid level switch mounted in brake fluid reservoir (Fig. 48).
7) Connect negative battery cable to battery post.
8) Fill master cylinder with clean, fresh Mopar Brake Fluid or equivalent.
WARNING: BE CERTAIN A FIRM BRAKE PEDAL IS ACHIEVED PRIOR TO ATTEMPTING VEHICLE OPERATION. IF A FIRM BRAKE PEDAL CANNOT BE ACHIEVED, BLEED ENTIRE BRAKE HYDRAULIC SYSTEM AND CHECK FOR LEAKS.
9) Road test vehicle to ensure proper operation of brakes.
Here are the directions for removing the old reservoir so you can install it on the new MC.
Master Cylinder (Fluid Reservoir)
Vehicle Brakes and Traction Control Hydraulic System Brake Master Cylinder Service and Repair Procedures Master Cylinder (Fluid Reservoir)
MASTER CYLINDER (FLUID RESERVOIR)
DISASSEMBLY - MASTER CYLINDER (FLUID RESERVOIR)
1) Clean master cylinder housing and brake fluid reservoir. Use only a solvent such as Mopar Brake Parts Cleaner or an equivalent.
2) Remove brake fluid reservoir cap. Using a syringe or equivalent type tool empty as much brake fluid as possible from the reservoir.
CAUTION: When removing fluid reservoir from the master cylinder, do not pry off using any type of tool. This can damage the fluid reservoir or master cylinder housing.
3) Remove the master cylinder assembly from the power brake vacuum booster.
4) Mount the master cylinder in a vise using the master cylinder mounting flange.
5) Using correct size pin punch, remove the two retaining pins between the fluid reservoir and master cylinder housing (Fig. 50).
6) Rock the brake fluid reservoir from side to side while pulling up to remove it from the seal grommets in master cylinder housing.
7) Remove the two master cylinder housing to brake fluid reservoir seal grommets (Fig. 51).
ASSEMBLY - MASTER CYLINDER (FLUID RESERVOIR)
1) Install new master cylinder housing to brake fluid reservoir sealing grommets in master cylinder housing (Fig. 51).
2) Lubricate reservoir mounting area with fresh clean brake fluid. Place reservoir in position over sealing grommets. Seat reservoir into sealing grommets using a rocking motion while firmly pressing down on fluid reservoir.
3) Be sure fluid reservoir is positioned properly on master cylinder. Bottom of fluid reservoir is to be touching the top of both sealing grommets when properly installed on master cylinder housing.
4) Install the two fluid reservoir to master cylinder retaining pins (Fig. 50).
5) Install the master cylinder assembly on the power brake booster.
6) Fill fluid reservoir to its proper level as indicated on the side of the fluid reservoir.
The aforementioned link provides the directions for bench bleeding the new master cylinder. Once this is all done, you will need to bleed the system. Start with the right rear, then left rear, then right front, then left front.
Let me know if this helps.
Images (Click to enlarge)
Friday, September 20th, 2019 AT 7:28 PM