27/05/2021
What to Do After Replacing Brake Pads: A Comprehensive Guide
Replacing your vehicle's brake pads is a significant maintenance task that, when done correctly, can restore your braking system's efficiency and safety. However, the job isn't quite finished once the new pads are installed. Several crucial steps and checks are necessary to ensure the new components bed in properly and the braking system functions as intended. This guide will walk you through the essential post-replacement procedures, with a particular focus on vehicles equipped with advanced systems like the Electromechanical Park Brake found in models such as the Passat.
Understanding Electromechanical Park Brake Systems
Modern vehicles, including the Passat, often feature an Electromechanical Park Brake (EPB) system integrated directly into the rear brake callipers. Unlike older systems, the EPB uses electric motors to retract the calliper pistons. This integration means that simply forcing the pistons back by hand is not an option. Instead, specific diagnostic software and procedures are required to retract them before you can even begin removing the old pads. This is a critical difference from conventional brake systems and requires specialist knowledge and tools.
Essential Tools for EPB Systems:
- Diagnostic Software Interface
- Battery Charger
- Standard workshop tools
When working with EPB systems, it is paramount to connect a battery charger to the vehicle's battery before initiating any procedures with the diagnostic equipment. This prevents voltage fluctuations that could damage the Electronic Control Unit (ECU) or other sensitive control systems. The EPB system typically has two motors within the rear callipers that control its operation. Adjustment and repositioning of these pistons can only be performed using the diagnostic tool, following a specific repositioning procedure.
Step-by-Step Aftercare for Brake Pad Replacement
Once the new brake pads have been fitted and the callipers reassembled, several important actions need to be taken. These steps are vital for ensuring the new pads and the overall braking system work safely and effectively.
1. The Crucial Pedal Pump
This is arguably the most important immediate step after replacing brake pads. Fully depress the brake pedal several times. This action is essential to reset the calliper pistons to their correct position against the new, thicker brake pads. Initially, the pedal will likely feel soft and go down further than usual. Continue pumping until a firm pedal feel returns. This process pushes the fluid back into the reservoir and ensures the pads are making contact with the brake disc.
2. EPB Piston Repositioning (for equipped vehicles)
For vehicles with an Electromechanical Park Brake, simply pumping the pedal is insufficient. The EPB pistons must be electronically reset to their home position. This is achieved using the diagnostic system. The procedure typically involves:
- Connecting the diagnostic tool to the vehicle.
- Navigating to the parking brake function.
- Selecting the 'reposition pistons' or 'service mode' function.
Important Note: While the diagnostic tool repositions the pistons, it's often necessary to manually ensure the piston is fully retracted, potentially by pressing the piston fully home using its presser mechanism as guided by the diagnostic software. Always refer to the manufacturer's specific instructions for your vehicle model.
3. Checking and Topping Up Brake Fluid
During the brake pad replacement, some brake fluid may have been pushed back into the reservoir as the pistons were retracted. It's crucial to check the brake fluid level in the reservoir. If it's low, top it up to the 'MAX' mark using the correct type of brake fluid specified for your vehicle. Brake fluid is hygroscopic, meaning it absorbs moisture from the air over time, which can lower its boiling point and lead to brake fade. It should be changed at regular intervals as per the vehicle's service schedule.
Warning: Never use brake fluid that does not comply with the specifications indicated by the manufacturer. Also, be extremely careful not to spill brake fluid onto painted surfaces, rubber, plastic, or mechanical components, as it can cause significant damage.
4. Cleaning and Lubrication
While not strictly a post-replacement step, ensuring the calliper slide pins are clean and lightly lubricated with a high-temperature molybdenum grease is vital for the longevity and smooth operation of the braking system. Any brake residue on moving surfaces should also be meticulously cleaned.
How do you lubricate brake pads?
Lubrication is applied to specific contact points to prevent noise and ensure smooth operation. A brake lubricant should be applied to the ends of the brake pad backing plates where they interface with the calliper. A thin coating can also be applied to the area of the shim that makes contact with the pistons. Crucially, avoid getting any lubricant on the piston dust boots or the friction material of the brake pad itself, as this will severely compromise braking performance.
5. Brake Disc Inspection and Cleaning
Before fitting new pads, the brake discs should be inspected for wear, scoring, or warping. If a disc is significantly worn or damaged, it should be replaced. Ensure the mating surfaces of the hub and the new disc are clean. The locating screw for the brake disc should be tightened to the manufacturer's specified torque, typically around 4 Nm.
6. Bedding-In New Brake Pads
New brake pads and discs need a 'bedding-in' or 'burnishing' period to ensure optimal performance. This process transfers a thin, even layer of pad material onto the disc surface, creating a uniform contact area. The procedure generally involves a series of moderate stops from around 50-60 mph down to 10-15 mph, without coming to a complete halt. Repeat this process 5-10 times, allowing a short cooling period between stops. Avoid harsh braking during the first few hundred miles.
Table: Bedding-in Procedure Summary
| Speed Range | Number of Stops | Braking Force | Cooling |
|---|---|---|---|
| 50-60 mph to 10-15 mph | 5-10 times | Moderate | Short cool-down between stops |
| First 200 miles | N/A | Avoid harsh braking | N/A |
Hydraulic System Checks and Bleeding
In some instances, particularly if the callipers were removed or the hydraulic system was opened, bleeding the brakes is necessary. This process removes any air that may have entered the system, which can lead to a spongy brake pedal.
Brake Calliper Bleeding:
This is performed if the calliper has been removed or overhauled. Loosen the bleed screw, fill with brake fluid until air-free fluid emerges, and then tighten the bleed screw.
Preliminary Bleeding Sequence:
- Simultaneously bleed front left and right callipers.
- Simultaneously bleed rear left and right callipers.
A pressure bleeding device is often used. Bleed screws are left loosened until air-free fluid emerges. The hydraulic unit may require a final bleed using the diagnostic tool's specific program.
Final Bleeding (Two-Operator Method):
- One operator presses and holds the brake pedal.
- The other operator loosens the bleed screw.
- The pedal is pressed fully down.
- The bleed screw is tightened while the pedal remains depressed.
- The pedal is released slowly.
This operation should be repeated 5 times for each brake calliper, following the sequence: Left Front, Right Front, Left Rear, Right Rear.
After any bleeding procedure, and indeed after any brake work, a road test is essential. This should include at least one instance of ABS braking to ensure the system is functioning correctly.
Frequently Asked Questions (FAQ)
Q1: How long does it take for new brake pads to bed in?
A1: The bedding-in process typically takes a few hundred miles of normal driving. During this period, it's best to avoid heavy or emergency braking.
Q2: Can I drive normally after replacing brake pads?
A2: Yes, but drive cautiously for the first few hundred miles. Avoid aggressive braking until the pads are properly bedded in. If you have an EPB system, ensure the reset procedure has been completed correctly.
Q3: What happens if I don't pump the brake pedal after replacing pads?
A3: The brake pedal will likely feel soft and spongy, and your braking performance will be significantly reduced until the pistons are manually or electronically pushed back into the callipers against the new pads.
Q4: Should I lubricate the back of the brake pads?
A4: Yes, a small amount of brake lubricant on the pad backing plate and shims (where they contact the piston) can help prevent brake squeal and ensure smooth operation. Do not get lubricant on the friction material.
Q5: Do I need to bleed the brakes after just changing pads?
A5: Generally, no, unless the hydraulic system was opened (e.g., calliper removal) or if you notice a spongy pedal after replacement. For EPB systems, the electronic reset is the critical step.
This technical article was kindly supplied by Federal-Mogul. If you’d like to find out more technical hints and tips from the company then log on to www.myferodo.com
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