Dorman M390320 Brake Master Cylinder Instructions

Dorman M390320 Brake Master Cylinder

Product Specifications

• Product Name: Step Bore Brake Master Cylinder
• Model Number: 1099758
• Recommended Fluid: New brake fluid from a sealed container
• Compatibility: Not recommended for use with DOT 5-rated brake fluid in ABS-equipped vehicles
• Instructions: Bench bleed the cylinder before installation on the vehicle

Product Usage Instructions

Step Bore Brake Master Cylinder Bench Bleeding

1. Secure the master cylinder in a vice by firmly clamping the mounting flange on the casting. Do NOT clamp the bore area of the cylinder to prevent distortion of the bore casting.
2. If the outlet ports have non-threaded protective caps, replace them with the provided threaded solid bleeder plugs.
3. Tighten bleeder plugs by gently tapping the casting (not the reservoir) with a plastic screwdriver handle or a wooden dowel to encourage air bubbles to escape during the bleeding process.
4. Fill the reservoir with new brake fluid from a sealed container.
5. Slowly depress and release the brake pedal multiple times to facilitate the bleeding process. Keep an eye on the fluid level in the reservoir and refill as needed.
6. Repeat the process until no more air bubbles are visible in the brake fluid.
7. Once bench bleeding is complete, install the master cylinder on the vehicle following manufacturer guidelines.
8. Perform a final bleeding of the entire brake system to ensure all air is removed before driving the vehicle.

Important Warnings

• Only use new brake fluid from a sealed container.
• Avoid reusing old brake fluid as it may introduce contaminants into the system.
• Do not use DOT 5-rated brake fluid in ABS-equipped vehicles to prevent foaming during ABS operation.
• Do not mix different DOT-rated brake fluids; flush the entire brake system if contamination occurs.

Maintenance Tips

1. Regularly check for leaks in the brake system and repair if any are found.
2. Maintain the proper fluid level in the reservoir to ensure optimal brake performance.
3. Always verify proper brake operation before driving the vehicle to ensure safety.

FAQ

Question: Why is bench bleeding necessary for the Step Bore Brake Master Cylinder?

Answer: Bench bleeding removes air from the cylinder bore, preventing air from entering the rest of the brake system and ensuring proper brake operation.

Question: Can I reuse old brake fluid for bench bleeding?

Answer: No, it is recommended to use only new brake fluid from a sealed container to avoid introducing contaminants into the system during bench bleeding.

Question: What should I do if I accidentally use DOT 5 rated brake fluid in an ABS equipped vehicle?

Answer: If DOT 5 rated brake fluid is used in an ABS equipped vehicle, foaming may occur during ABS operation. It is advised to flush the entire brake system to remove the contaminated fluid and refill with the correct type of brake fluid.

Safety Instruction

• ATTENTION – Refer to the appropriate service manual for your vehicle to obtain specific service procedures for this part. If you do not have a service manual or lack the skill to install this part, it is recommended that you seek the services of a qualified technician. Pay special attention to all cautions and warnings included in the service manual! Read and follow all instructions carefully! ABS-equipped cars may require special bleeding and installation procedures! Consult the service manual for specific procedures.
• WARNING! This Brake Master Cylinder MUST be bench-bled before installation on the vehicle! This process will remove air from the cylinder bore. Failure to bench bleed the cylinder will result in air being introduced into the rest of the brake system. DO NOT OPERATE THE VEHICLE UNTIL NORMAL BRAKE OPERATION IS OBTAINED!
• WARNING! Use only new brake fluid from a sealed container! Do not reuse old brake fluid! DO NOT USE DOT 5-rated brake fluid in ABS-equipped vehicles! Foaming of the brake fluid will take place during the ABS operation. Do not mix different DOT-rated brake fluids! Flush the entire brake system to remove all contaminated fluid.

INSTALLATION INSTRUCTIONS

STEP BORE BRAKE MASTER CYLINDER BENCH BLEEDING INSTRUCTIONS

1. Secure the master cylinder in a vice by firmly clamping the mounting flange on the casting. DO NOT CLAMP THE BORE AREA OF THE CYLINDER! DISTORTION OF THE BORE CASTING WILL OCCUR!

2. If the outlet ports have non-threaded protective caps installed, replace them with the provided threaded solid bleeder plugs. Tighten bleeder plugs by hand to seat. Note: The plugs must be tightened enough to keep air from entering the master cylinder through the ports, but over-tightening will result in stripping the plastic threads and rendering them useless.

3. Fill the reservoir with the appropriate brake fluid.

4. Using a blunt instrument or wooden dowel to avoid piston damage, slowly depress the piston into the bore using no more than a 1-inch stroke. Do not bottom out the piston.

5. Slowly release the piston to rest position. Wait 15 seconds to avoid fluid aeration.

6. Repeat steps 4 and 5 until air bubbles cease to appear in both reservoir chambers and the piston cannot be depressed any more than 1/8 inch.

7. The unit is finished with the bench bleeding process. Ensure the reservoir lid is secure and release the master cylinder from the vice. Proceed to installation instructions.
   TECH TIP: Gently tapping the casting (not the reservoir) with a plastic screwdriver handle or a wooden dowel will encourage the air bubbles to escape from the bore during the bleeding process.
   BRAKE MASTER CYLINDER INSTALLATION INSTRUCTIONS
   IMPORTANT: When bleeding step bore design master cylinders, you must wait 15 seconds after releasing the piston to avoid fluid aeration.

8. Leave the bleeder plugs in the ports and install the master cylinder on the vehicle.

9. Tighten brake line nuts to the specifications found in the service manual. Do not over-tighten! Damage to threads may occur!

10. After installing the master cylinder, flush the entire brake system with fresh fluid from a sealed container.

11. Refer to the service manual for specific bleeding/flushing procedures, especially when dealing with split-diagonal brake systems and ABS-equipped vehicles.

12. Check for leaks and repair if found. Maintain proper fluid level in the reservoir.

13. Check for proper brake operation before driving the vehicle.

TECH TIPS

• When bleeding the brake system, ensure the master cylinder is level. The rear of the vehicle may have to be raised if the master cylinder is mounted at an angle.
• Use caution when handling brake fluid. Prevent contact with skin, face, eyes, and painted surfaces.
• DO NOT, under any circumstances, introduce any petroleum-based fluids (gas, engine oil, power steering fluid, transmission fluid, etc.), to the brake system! Failure (swelling) of all rubber components will occur!
• Brake fluid absorbs moisture. Never reuse old brake fluid! Always use fresh brake fluid from a sealed container.
• If bench bleeding the master cylinder was successful, and the brake pedal becomes softer after installing to the vehicle, verify the entire brake system. The issue is not the master cylinder.

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