Fixing a Broken Brake Caliper

A malfunctioning brake caliper can be a serious safety concern, compromising your vehicle's ability to stop effectively. The caliper, housing the piston that presses the brake pads against the rotor, relies on internal seals to prevent fluid leaks. When these seals fail, brake fluid can escape, leading to a spongy pedal and significantly reduced braking power. While complete caliper failure is dangerous, understanding how to identify and replace a faulty caliper can save you money and ensure your safety on the road. This guide will walk you through the process, from identifying the problem to getting your vehicle back in safe working order.

Understanding Brake Caliper Function and Failure

The brake caliper is a crucial component of your vehicle's disc braking system. Its primary role is to house the brake piston, which, when activated by hydraulic pressure, forces the brake pads into contact with the brake rotor. This friction slows and stops the vehicle. Inside the caliper, a square seal around the piston is vital for preventing brake fluid from leaking out and allowing the piston to move smoothly. Over time, or due to contamination, these seals can degrade and fail. This failure can be caused by:

• Wear and Tear: Like any mechanical part, seals can wear out with age and use.
• Contamination: Dirt, rust, and moisture within the brake lines can corrode and damage the seals. Regular brake bleeding is essential to keep the fluid fresh and free of contaminants.
• Corrosion: If brake fluid leaks, moisture can enter the caliper, leading to rust and further seal damage.

Recognising the signs of a failing caliper is key. These can include a spongy or soft brake pedal, a warning light on your dashboard, unusual noises when braking, or a visible fluid leak around the wheel.

Can You Rebuild a Brake Caliper?

While it is technically possible to rebuild a brake caliper by replacing the internal seals and piston, it's often a more complex and time-consuming process than replacing the entire caliper. Rebuilding typically requires specialised tools to safely remove and install the piston and seals. For most DIY mechanics, purchasing a new or reconditioned caliper is a more straightforward and often more reliable solution. If you have the basic tools for changing brake pads, you likely have most of what you need to swap out a caliper.

Part 1: Removing the Old Caliper

Before you begin, ensure you have a safe and level working surface. Safety is paramount when working with vehicle brakes.

Materials Needed:

Note: Socket sizes will vary by vehicle make and model. Common sizes for caliper slider pin bolts and mounting bolts are 14mm or ⅝”. Lug nut sizes are typically 19mm or 20mm for metric vehicles, and ¾” or 13/16” for older domestic vehicles.

Step-by-Step Removal:

1. Lift the Vehicle: Use your jack to raise the vehicle off the ground on a solid, level surface. Securely place jack stands beneath the vehicle's frame for support. Block any wheels still on the ground to prevent rolling. Tip: Loosen the lug nuts slightly before lifting the vehicle.
2. Remove the Wheel: This will provide access to the caliper and rotor. Tip: Keep track of your lug nuts by placing them in a tray or an overturned hubcap.
3. Remove the Top Slider Pin Bolt: This allows the caliper to pivot open, facilitating brake pad removal. If this bolt is not removed, the pads may fall out when the caliper is detached.
4. Open the Caliper Housing: The caliper housing can usually be rotated upwards, much like a clam shell, to expose the brake pads. Tip: A flathead screwdriver or small pry bar can help if the caliper is difficult to open.
5. Close the Caliper: With the brake pads removed, close the caliper and hand-tighten the slider bolt to hold the components together temporarily.
6. Loosen the Banjo Bolt: While the caliper is still attached to the hub, carefully loosen the banjo bolt connecting the brake line. Tighten it lightly afterwards to prevent significant fluid leakage. This is easier to do while the caliper is secured. Note: Have rags ready to catch any leaking brake fluid.
7. Remove One Caliper Mounting Bracket Bolt: Locate and unscrew one of the bolts securing the caliper mounting bracket. These are typically found on the backside of the wheel hub. Tip: Manufacturers often use thread locker on these bolts. A breaker bar may be necessary to loosen them.
8. Support the Caliper: Before removing the second bolt, ensure you have a firm grip on the caliper to support its weight. Calipers can be heavy, and letting them hang by the brake line can cause damage. Tip: Position yourself as close as possible to the caliper for better support.
9. Remove the Second Caliper Mounting Bracket Bolt: With the caliper supported, remove the second mounting bolt.
10. Secure the Caliper: Do not let the caliper dangle from the brake line. Use a bungee cord or sturdy wire to tie the caliper to a suspension component. Tip: Ensure the bungee cord is wrapped securely to prevent the caliper from falling. Alternatively, place it on a sturdy box.
11. Secure the Rotor: Screw two lug nuts back onto the wheel studs to hold the rotor in place. This will make installing the new caliper easier.

Part 2: Setting Up the New Caliper

Proper preparation of the new caliper and its mounting hardware is crucial for a secure and long-lasting installation.

Step-by-Step Setup:

1. Clean and Apply Thread Locker: Clean the caliper mounting bolts and bracket bolts thoroughly using brake cleaner and a wire brush. Ensure they are completely dry before applying new thread locker, if it was used originally.
2. Install the New Caliper and Mount: Begin by screwing in the top mounting bolt a few turns. This will help align the bottom bolt hole.
3. Torque Mounting Bolts: Tighten the mounting bolts to the manufacturer's specified torque. This information can usually be found in your vehicle's repair manual or online. Note: Overtightening can weaken the metal, while undertightening can lead to loosening due to vibrations.

Part 3: Transferring the Brake Line to the New Caliper

This step involves carefully disconnecting the old brake line and connecting it to the new caliper, ensuring a leak-free seal.

Step-by-Step Transfer:

1. Remove Banjo Fitting from Old Caliper: Unscrew the bolt holding the banjo fitting to the old caliper. Have rags ready to catch the brake fluid.
2. Remove Old Washers: Remove the old copper or aluminium washers from the banjo fitting and the banjo bolt. New washers will be included with your new caliper. Clean the banjo bolt with brake cleaner. These washers are crush washers, designed to deform slightly to create a tight seal. Note: Failure to replace old washers can result in leaks.
3. Install New Washers: Place one new washer between the banjo fitting and the new caliper, and the other new washer onto the banjo bolt.
4. Tighten Banjo Bolt: Use a torque wrench to tighten the banjo bolt to the manufacturer's specified torque.

Part 4: Reassembling and Final Steps

With the new caliper installed and the brake line connected, it's time to reassemble the rest of the components and prepare for brake bleeding.

Step-by-Step Reassembly:

1. Reinstall Brake Pads: Open the caliper by removing the top slider bolt and install the new brake pads. Note: Ensure you have the correct size bolts for the new caliper.
2. Install Anti-Vibration Clips: If your new caliper came with them, install the anti-vibration clips (also known as pad shims or hardware). These prevent rattling. If not included, you can reuse the old ones. Tip: Refer to the old caliper for correct placement.
3. Lubricate Pad Contact Points: Apply a thin layer of silicone-based lubricant to the back of the brake pads where they contact the caliper and the slider pins. This helps prevent squeaking and ensures smooth operation. Note: Avoid getting lubricant on the pad friction material or the rotor surface.
4. Close Caliper and Tighten Slider Bolt: Close the caliper and tighten the top slider bolt to the specified torque.
5. Prepare for Bleeding: Slightly loosen the bleeder valve on the caliper. This will allow air to begin escaping. Have rags positioned to catch any dripping fluid. You may want to open the master cylinder cap to facilitate fluid flow.
6. Bleed the Brakes: This is a critical step to remove air from the brake lines, ensuring a firm brake pedal. You only need to bleed the lines for the caliper(s) you replaced. Warning: Never let the brake fluid reservoir run dry during bleeding, as this will introduce more air into the system. Check the fluid level frequently. Note: The order of bleeding is important. Typically, you start with the caliper furthest from the master cylinder and work your way closer. Consult your vehicle's manual for the correct procedure.Tip: Bleeding is much easier with a second person to operate the brake pedal.
7. Reinstall the Wheel: Once the brakes are bled and all components are clean, reinstall the wheel. Hand-tighten the lug nuts, then snug them with a wrench. Lower the vehicle and torque the lug nuts to the manufacturer's specification in a star pattern.
8. Test Drive: Begin with a slow, cautious test drive in a safe area. Gently apply the brakes to ensure they are functioning correctly. Listen for any unusual noises and check for leaks, particularly around the banjo fitting.

Common Questions and Answers

Q1: How do I know if my brake caliper is bad?

Signs of a bad brake caliper include a spongy brake pedal, the vehicle pulling to one side when braking, squealing or grinding noises, a burning smell, and visible brake fluid leaks around the wheels.

Q2: Can I just replace the brake pads instead of the caliper?

If the caliper itself is leaking fluid, sticking, or the piston is seized, you will need to replace the caliper. If the caliper is functioning correctly, you can often just replace the brake pads and possibly the rotors.

Q3: How much does it cost to replace a brake caliper?

The cost can vary significantly depending on the vehicle, the type of caliper (new vs. reconditioned), and whether you do the work yourself or have a mechanic do it. Parts can range from £100 to £300+, with labour adding several hundred pounds if done professionally.

Q4: Do I need to bleed the brakes after replacing a caliper?

Yes, absolutely. Replacing a caliper involves disconnecting the brake line, which introduces air into the hydraulic system. Bleeding is essential to remove this air and restore proper brake function.

Q5: What is thread locker used for on brake caliper bolts?

Thread locker (like Loctite) is used to prevent bolts from loosening due to vibration. It's important to use the correct type (usually blue or red) and apply it as per the manufacturer's recommendations.

By following these steps carefully and prioritising safety, you can successfully replace a faulty brake caliper and restore your vehicle's braking performance. Regular brake maintenance, including periodic bleeding, is key to extending the life of your brake components and ensuring your safety.