Alcon Caliper Bleeding & Piston Retraction

When working with high-performance braking systems, particularly those manufactured by Alcon, understanding the correct procedures for bleeding the brake system and retracting the caliper pistons is paramount. These steps are crucial not only for ensuring optimal braking performance but also for the longevity and reliability of your braking components. Improper bleeding or piston retraction can lead to a spongy pedal, reduced braking efficiency, and in worst-case scenarios, a complete loss of braking power. This guide will walk you through the essential steps, drawing upon best practices and specific considerations for Alcon calipers.

Understanding the Importance of Proper Bleeding

Brake fluid is hygroscopic, meaning it absorbs moisture from the atmosphere over time. This absorbed water can lower the boiling point of the brake fluid, leading to brake fade under heavy use. Air can also enter the system through various means, such as during maintenance or due to leaks. Air, being far more compressible than brake fluid, will cause the brake pedal to feel spongy and unresponsive. The primary goal of bleeding the brakes is to remove all air and old, contaminated fluid from the system, replacing it with fresh, high-quality brake fluid. For Alcon systems, precision is key to achieving the desired firm pedal feel.

Essential Tools and Preparation

Before you begin, ensure you have the necessary tools and materials:

• Fresh, high-quality brake fluid (check your Alcon system's specifications for the correct type, often DOT 4 or DOT 5.1).
• A bleed bottle with a one-way valve or a dedicated brake bleeding kit.
• Clear plastic tubing that fits snugly onto the bleed screws.
• Appropriate wrenches for the bleed screws (usually combination wrenches).
• A brake fluid catch pan.
• Gloves and eye protection.
• Clean rags.
• New pad backplates or very thin brake pads for piston retraction.
• A helper, if not using a vacuum or pressure bleeding system.

Crucially, always work in a well-ventilated area and protect painted surfaces from brake fluid, as it can damage paint. Ensure the vehicle is safely supported if it needs to be raised.

Step-by-Step Bleeding Procedure

The following procedure outlines the recommended method for bleeding Alcon calipers. It's designed to remove air effectively and achieve a firm pedal.

Initial System Fill (Gravity Bleeding)

1. Connect a bleed bottle and tubing to each caliper's bleed screw. Ensure the tubing is securely attached to prevent leaks or air ingress.
2. Remove the reservoir cap and fill the brake fluid reservoir to the MAX line. Do not replace the cap at this stage.
3. Open the bleed screws on each caliper one by one. Allow the fluid to gravity-fill the system until clean fluid is observed flowing through the tubing into the bleed bottle.
4. Continuously monitor the fluid level in the reservoir, ensuring it never drops below the outlet opening. If it does, air will be drawn into the system, negating your efforts.
5. Once clean fluid is observed from all bleed points, securely close all bleed screws.

Bleeding Dual Master Cylinders and Multi-Bleed Screw Calipers

If your vehicle uses dual master cylinders (common in racing applications), you'll need to bleed one front and one rear caliper together to ensure balanced pressure. For Alcon calipers equipped with two bleed screws (one inner and one outer), always bleed the outer bleed screw first, followed by the inner bleed screw.

The Pedal Pumping Fallacy

Never attempt to bleed the brakes by repeatedly pumping the brake pedal until it feels firm and then opening the bleed screws. This method, often referred to as 'pump and bleed', can actually introduce more air into the system or aerate the fluid already present, making it significantly harder to remove. The correct method involves a slow, controlled pedal application.

Master Cylinder Feed Lines and Air Escape

Air trapped in the master cylinder's primary and secondary chambers should naturally escape back into the reservoir via the feed lines when the brake pedal is released. However, any restrictions in these feed lines or at the reservoir connection can prevent this. If air remains trapped in the feed line, it can be drawn back into the master cylinder during the recuperation stroke (when the pedal is released). To minimise this risk, it is recommended to use dash 4 (or equivalent specification) brake hoses and fittings, especially if the reservoir outlet is positioned close to the master cylinder inlet. This ensures a clear, unobstructed path for air to return to the reservoir.

The Correct Bleeding Sequence

With the preparation complete, you can now proceed with the actual bleeding:

1. Open the outer bleed screw on one front and one rear caliper.
2. Slowly and deliberately depress the brake pedal, utilising the full stroke of the master cylinder. Avoid rapid pedal application, as this can aerate the fluid.
3. Once the pedal reaches its lowest point, close the bleed screws securely.
4. Allow the brake pedal to return to its original, fully released position at a controlled rate. Do not let it snap back. This allows the master cylinder to recuperate fresh fluid from the reservoir.
5. Wait for approximately 5 seconds before the next pedal application. This waiting period allows the master cylinder to completely re-fill with fluid.
6. Check the reservoir level and top it up as necessary.
7. Repeat steps 1-6 until no air bubbles are visible in the bleed tube for that caliper. For most systems, a clear fluid run should be achieved within 3-5 pedal strokes per bleed screw.
8. Repeat the entire process (steps 1-7) for the inner bleed screws of the front and rear calipers.
9. Transfer to the other side of the car and repeat steps 1-8 for the remaining calipers.
10. If, after completing the full bleeding sequence, the brake pedal still feels soft or has excessive travel, repeat the entire procedure from step 1.

Backbleeding: An Alternative Method

If, after diligently following the above steps, the pedal remains unsatisfactory, it indicates that stubborn air is still trapped within the system. In such cases, backbleeding is the recommended alternative. This method involves introducing fresh brake fluid from the caliper bleed screw upwards towards the master cylinder. A large volume of fluid is pushed through the system, effectively carrying any trapped air back to the reservoir via the master cylinder's inlet port. This is often performed using a specialised pressure bleeder connected to the bleed screw, or with a syringe-based system.

Calibrating Alcon Caliper Pistons

Once the brake system is bled and a firm pedal is achieved, the next critical step is to retract the caliper pistons. This is essential for fitting new, thicker brake pads or when the vehicle has been sitting, causing the pistons to extend slightly. Improper retraction can lead to the new pads dragging on the discs, causing premature wear and heat buildup.

The Piston Retraction Process

1. Prepare the Calipers: Fit new, thin brake pads or, preferably, just the pad backplates into each Alcon caliper. This provides a clean surface for the pistons to push against and ensures maximum retraction.
2. Initial Piston Movement: Slowly and gently pump the brake pedal. This will push the caliper pistons forward until they just make contact with the fitted backplates or thin pads.
3. Retracting the Pistons: Working on one caliper at a time, use a suitable C-clamp or a dedicated brake piston retraction tool to carefully and slowly squeeze the caliper pistons back into their bores. As you retract the pistons, brake fluid will be displaced back into the master cylinder reservoir.
4. Manage Reservoir Level: Keep a close eye on the brake fluid reservoir. As fluid is displaced, the level will rise. Be prepared to carefully remove excess fluid from the reservoir using a syringe or clean rag to prevent it from overflowing.
5. Repeat for All Calipers: Complete this retraction process for all pistons in all calipers.
6. Refit Pads and Pressurise: Once all pistons are retracted, refit your new, correct-thickness brake pads. Ensure they are seated correctly.
7. Final Pedal Check: Before driving, slowly depress the brake pedal again. It should feel firm, and the pistons should now be correctly positioned against the new pads.

Final Checks and Important Considerations

Leak Detection

After completing the bleeding and piston retraction, it is absolutely vital to thoroughly inspect the entire brake system for any signs of leaks. Check all connections, bleed screws, and the flexible hoses for any dampness or seepage of brake fluid.

Bleed Screw Torque

When tightening the bleed screws, use the recommended torque specification. Overtightening can damage the bleed screw or the caliper body, leading to leaks. A common torque range for bleed screws is typically around 7-10 Nm, but always consult your Alcon system's service manual for precise figures.

Achieving a Firm Pedal

The ultimate goal when bleeding Alcon brakes is to achieve a firm brake pedal that remains solid and does not drift downwards under sustained pressure. It is not uncommon for the pedal feel to improve further after a short period of driving. A light re-bleed after some initial use can sometimes refine the pedal further.

Balance Bar Alignment (Dual Master Cylinder Systems)

For vehicles equipped with dual master cylinders and a balance bar, there is a critical alignment to achieve. IMPORTANT: When the normal maximum brake pedal load is applied, the threaded rod of the balance bar should be precisely at a right angle (90 degrees) to the master cylinder push rods. Incorrect balance bar adjustment can lead to uneven braking force between the front and rear wheels, affecting vehicle stability and braking performance.

Summary Table of Bleeding Steps

Frequently Asked Questions

Q1: How often should I bleed my Alcon brakes?

It's recommended to bleed your brake system every 12-24 months, or whenever you notice a spongy pedal, after replacing brake fluid, or after any work has been done on the brake lines or calipers.

Q2: Can I use a vacuum bleeder on Alcon calipers?

Yes, vacuum bleeders can be effective, but care must be taken not to introduce air into the system through the bleed screw threads if the vacuum is too strong or the seal is poor.

Q3: What happens if I overfill the reservoir?

Overfilling can lead to brake fluid being expelled from the reservoir due to expansion from heat, potentially damaging paintwork and creating a slip hazard.

Q4: Is it normal for the brake fluid to change colour?

Yes, brake fluid can darken over time as it absorbs contaminants and moisture. This is a good indicator that it's time for a fluid change and bleed.

By adhering to these detailed procedures, you can ensure your Alcon braking system is functioning at its peak performance, providing the confidence and safety you expect from such high-quality components.