A. Replace the Master Cylinder Primary Piston

1. With the engine not running, pump the brake pedal until a firm pedal is achieved (4-5 strokes).

Caution:
Vacuum in the brake booster must be pumped down before removing the master cylinder from the brake booster.

2. Thoroughly clean all surfaces of the filler neck, brake fluid reservoir, master cylinder and the attaching area of the brake booster with Mopar Glass Cleaner (PN 4318014) or equivalent. Be sure to wear safety goggles and use compressed air to remove excess cleaner.





3. Disconnect the low brake fluid level switch electrical connector (Figure 1).

4. Disconnect the wiper module drain hose.





5. Disconnect the primary and secondary brake tubes from the master cylinder (Figure 2). Install the provided plugs into the master cylinder outlet ports and cap the brake tubes.

NOTE:
Do not drip brake fluid on painted surfaces as this may damage the paint. If brake fluid does contact a painted surface, immediately flush with water and wipe with a clean towel to remove all brake fluid from the surface.





6. Remove the two (2) master cylinder attaching nuts (Figure 3).

7. Slide the master cylinder straight out of the power brake booster.

8. Remove the reservoir cap from the filler neck. Drain the brake fluid from the master cylinder reservoir and then re-install the cap.

NOTE:
Do not attempt to remove the filler neck as this may cause leakage or damage to the filler neck.





9. Clamp the master cylinder in a vise, horizontally with the reservoir up, using only the mounting flange (Figure 4).

Caution:
When clamping the master cylinder in the vise, clamp only on the mounting flange as shown. Do not clamp on the primary piston, seal or body of the master cylinder.

10. Thoroughly clean the exterior of the master cylinder and reservoir.

11. Using a plastic trim stick, carefully remove the vacuum seal from the groove in the master cylinder flange and discard. Do not attempt to pry the seal off the master cylinder by inserting a sharp tool between the seal and the master cylinder casting. This may scratch the casting and prevent a proper seal.

IMPORTANT:
Use CLEAN HANDS for all of the following disassembly and assembly procedures. ANY contamination inside the master cylinder bore or reservoir may result in partial brake system loss after the vehicle is returned to the customer.

12. Depress the primary piston slightly to remove load from the snap-ring. While holding the piston in this position, remove the snap-ring using snap-ring pliers. Discard the snap-ring.

Note:
Do not use the provided piston assembly tool to remove the old piston. This may contaminate the tool and damage the new piston during assembly.





13. Carefully pull the primary piston assembly and pin out of the bore and discard (Figure 6). The Primary Spring is not part of the piston assembly, but may be pulled out with it. If this occurs, gently push the spring back into the bore while removing the piston assembly. Ensure that the pin is removed with the primary piston assembly, and is not left in the cylinder bore.

Caution:
Be careful not to scratch or contaminate the new primary piston. DO NOT remove the blue installation tool from the new piston assembly.

Note:
The blue piston installation tool protects the piston surface during the assembly procedure, helps retain the pin in the piston assembly, and serves as an inspection device to ensure proper assembly.





14. With clean hands, rinse the inside of the master cylinder and lubricate the piston pumping cup and guide O-ring seal on the new primary piston assembly with clean brake fluid conforming to DOT 3 specifications (Figure 7).

15. The primary piston assembly has a pin installed into a hole in the piston. If the pin was dislodged from the assembly during shipping and handling, re-insert the pin into the hole in the primary piston (Figure 7). Orientation of the slot at the end of the pin is not important. If necessary, pull the piston guide back slightly to insert the pin.

16. Push on the end of the blue installation tool to slide the guide tight against the pin. This will retain the pin in the piston assembly. Make sure the pin is centered in the piston as shown in Figure 7 and does not extend beyond the piston flange on either side.

Caution:
Be careful not to allow the pin to fall out of the assembly during installation. If the pin falls out of the assembly for any reason, make sure that the pin is clean and undamaged before reinstalling.





17. Insert the new piston assembly into the cylinder bore, seal end first (Figure 8). Ensure that the pin remains centered in the piston.

Caution:
Do not insert a screwdriver or other sharp objects into the end of the primary piston. This may damage the booster rod contact surface.

18. With the piston installation tool still in place over the piston, slide the new snap-ring in place over the installation tool.

Caution:
Make sure that the piston installation tool is tight against the piston guide and does not allow the snap-ring or snap-ring pliers to contact the primary piston during assembly.

19. Grasp the snap-ring with snap-ring pliers, then press on the end of the installation tool until the guide seats in the cylinder bore and the snap-ring groove is visible.

20. While depressing the piston with the installation tool, install the snap-ring into the snap-ring groove.

21. Verify that the snap-ring is properly installed in its groove by depressing and releasing the installation tool several times. Visually check to make sure the snap-ring is properly seated.





22. Install the provided vacuum seal into the master cylinder flange groove (Figure 9). Make sure that the seal is fully inserted and sits squarely in the groove.

Caution:
DO NOT reuse the old vacuum seal. A NEW vacuum seal MUST be installed on the master cylinder to prevent vacuum leaks.

23. With the installation tool pressed against the piston guide, check to make sure that the end of the piston is recessed slightly into the piston installation tool (Figure 8). If the piston is flush with or extends beyond the end of the tool, the pin is not properly installed in the piston assembly and the installation procedure must be repeated.

24. Using a CLEAN shop rag or paper towel, remove any fluid from the end of the casting and the snap-ring groove area. Inspect to make sure that no dirt or other debris is present in this area.

25. Remove the installation tool from the primary piston and DISCARD. Do not re-use the tool.

26. With installation tool removed, install the new boot over the primary piston and master cylinder body (Figure 9). Ensure that the rear (smaller) end of the boot is installed in the groove at the end of the primary piston, and the front (larger) end of the boot is slipped over the end of the body. There should be no wrinkles in the boot.

27. Depress piston fully by hand to make sure piston moves freely.





28. Attach Miller Special Tool # 8129 bleed tubes to the primary and secondary outlets. Due to the filler neck on the reservoir, the bleed tubes must be gently bent so that the ends exit into a separate container (Figure 10). Fill the separate container and the master cylinder reservoir with clean brake fluid that conforms to DOT 3 specifications. Bench bleed the master cylinder using the provided dowel rod. Slowly depress the pistons to the stop, then allow the pistons to return to the fully released position. Repeat this step several times after all air bubbles are expelled from the bleed tubes. This will ensure all air is bled from the master cylinder. Replenish the reservoir with CLEAN brake fluid as required. DISCARD brake fluid collected in the container. Do not pour this into the master cylinder reservoir.

Caution:
^ DO NOT use a screwdriver or other sharp object to perform the bleed procedure. This may damage booster rod contact surface.

^ DO NOT attempt to separate the master cylinder filler neck from the reservoir as this may cause leakage or damage the filler neck.

Note:
DO NOT install the master cylinder without following the above bench bleeding procedure. When this procedure is followed, it is not necessary to bleed the entire vehicle brake system.

29. Remove the bleed tubes from the master cylinder outlet ports. Plug the outlet ports with the supplied plugs, top off the reservoir with brake fluid and install the filler neck cap.

30. Remove and inspect the inside of the boot to make sure that there is no accumulation of brake fluid. Fluid puddling in the boot, is caused by an improperly installed pin, or a damaged rear seal.

31. Re-install the boot.