Dorman M39498 Brake Master Cylinder Instructions

Dorman M39498 Brake Master Cylinder

Product Information

Specifications

• Product Name: Step Bore Brake Master Cylinder
• Model Number: 1099758
• Compatibility: Suitable for bench bleeding before installation on vehicles
• Fluid Compatibility: New brake fluid from a sealed container, not compatible with DOT 5-rated fluid in ABS-equipped vehicles

Product Usage Instructions

Step Bore Brake Master Cylinder Bench Bleeding Instructions

1. Secure the master cylinder in a vise by firmly clamping the mounting flange on the casting. Do NOT clamp the bore area to prevent distortion.
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) 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 bleed air from the cylinder bore.
6. Continue bleeding until no air bubbles are visible in the fluid.
7. Recheck the tightness of bleeder plugs and mounting flange.
8. Remove the master cylinder from the vise once bench bleeding is complete.

Important Notes

• Do not operate the vehicle until normal brake operation is obtained.
• Avoid mixing different DOT-rated brake fluids to prevent issues.
• Flush the entire brake system to remove any contaminated fluid.
• Check for leaks and repair if found before driving the vehicle.

Frequently Asked Questions (FAQ)

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

• A: Bench bleeding removes air from the cylinder bore, preventing air from entering the rest of the brake system during installation.

Q: Can I reuse old brake fluid during bench bleeding?

• A: No, it is recommended to use only new brake fluid from a sealed container to ensure proper brake system performance.

Q: What should I do if I encounter foaming of brake fluid during ABS operation?

• A: Avoid using DOT 5-rated brake fluid in ABS-equipped vehicles to prevent foaming. Flush the system and use compatible fluid as needed.

Usage Instructions

STEP BORE BRAKE MASTER BLEEDING INSTRUCTIONS

• 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.

STEP BORE BRAKE MASTER CYLINDER BENCH BLEEDING INSTRUCTIONS

1. Secure the master cylinder in a vise 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 vise. 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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