20/07/2013
For any motorist, the braking system is arguably the most critical component of their vehicle, directly impacting safety on the road. Your Subaru, renowned for its reliability and performance, relies on a meticulously engineered braking system to ensure every journey is secure. While Subaru brake pads are crafted for durability and consistent stopping power, like all wear-and-tear components, they will eventually require attention. Whether it's due to natural wear over miles of driving or a conscious decision to enhance stopping performance, particularly in challenging British weather conditions, understanding when and how to maintain your Subaru's brakes is paramount. This comprehensive guide will delve into the nuances of Subaru brake pad replacement and the essential steps involved in tackling a brake caliper change, empowering you with the knowledge to keep your vehicle performing at its best.
Understanding Your Subaru's Braking System
Your Subaru's braking system is a complex network designed to convert the kinetic energy of motion into heat through friction, bringing your vehicle to a controlled halt. At its heart are the brake pads and calipers. When you press the brake pedal, hydraulic pressure forces the brake fluid through lines to the calipers. The caliper, in turn, squeezes the brake pads against the rotor (a disc attached to the wheel hub), creating the friction necessary to slow or stop the vehicle. Given this vital role, regular inspection and timely replacement of components are non-negotiable.
When Do Subaru Brake Pads Need Changing?
Subaru brake pads are designed to provide years of smooth, trouble-free stopping power. However, the day will inevitably come when you need to change them out. This isn't just about preventing mechanical failure; it's about maintaining peak performance and ensuring your Subaru stops on a dime, even during the rainy season or in emergency situations. Recognising the signs of worn brake pads is crucial for your safety and that of others on the road.
- Audible Cues: The most common indicator is a high-pitched squealing sound when you apply the brakes. Many brake pads incorporate a small metal tab, known as a wear indicator, designed to make contact with the rotor when the pad material wears down to a critical level. If you hear this, it's a clear signal to check your pads. A deeper grinding noise, however, signifies a much more severe issue: metal-on-metal contact, meaning the pad material is completely gone, and the backing plate is grinding against the rotor. This requires immediate attention, as it can severely damage your rotors and calipers.
- Reduced Braking Performance: If your Subaru feels like it's taking longer to stop, or if the brake pedal feels spongy and goes further to the floor than usual, your pads may be excessively worn. You might also notice a pulsating or vibrating sensation through the brake pedal or steering wheel, which could indicate warped rotors due to prolonged use with thin pads, or uneven pad wear.
- Visual Inspection: You can often visually inspect your brake pads by looking through the spokes of your wheels. Each pad should have at least 3-4mm of friction material remaining. If it looks thinner than a 20p coin, it's time for replacement. Uneven wear across the pads on the same axle can also indicate a problem with the caliper or rotor.
- Dashboard Warning Light: Some newer Subaru models are equipped with electronic wear sensors that will illuminate a warning light on your dashboard when the pads are worn down.
The Lifespan of Brake Pads
The lifespan of brake pads varies significantly depending on several factors:
- Driving Habits: Aggressive driving, frequent heavy braking, and city driving with lots of stop-and-go traffic will wear pads down much faster than gentle, long-distance motorway driving.
- Vehicle Load: Regularly carrying heavy loads or towing puts more strain on the braking system, leading to quicker wear.
- Terrain: Driving on hilly or mountainous terrain often requires more braking, accelerating pad wear.
- Brake Pad Material: Different materials offer varying lifespans and performance characteristics.
Types of Brake Pads: Choosing Wisely
When it comes to replacing your Subaru's brake pads, you'll encounter a few common types, each with their own characteristics:
| Pad Type | Pros | Cons | Ideal Use |
|---|---|---|---|
| Organic Non-Asbestos (NAO) | Quiet, soft on rotors, good initial bite | Higher dust, shorter lifespan, less fade resistance | Daily driving, light-duty, older vehicles |
| Semi-Metallic | Good stopping power, durable, excellent heat transfer | Noisier, more brake dust, can be harder on rotors | Performance driving, heavy-duty, most modern vehicles |
| Ceramic | Very quiet, low dust, long lifespan, consistent performance | Higher cost, less effective in extreme cold, can require more pedal force | Luxury vehicles, daily driving, performance upgrades |
For most Subaru owners, a good quality semi-metallic or ceramic pad will provide an excellent balance of performance, durability, and quiet operation.
The Critical Role of Brake Calipers
While brake pads are the consumable friction material, the brake caliper is the component that holds the pads and presses them against the rotor. It contains a piston (or multiple pistons) that moves outward when hydraulic pressure is applied. Calipers are generally robust, but they can seize, leak, or become damaged over time due to dirt, corrosion, or extreme heat. A faulty caliper can lead to uneven pad wear, pulling to one side when braking, or a complete loss of braking power on one wheel.
A Step-by-Step Guide to Replacing Your Brake Caliper
Replacing a brake caliper is a more involved task than just changing pads, as it requires opening the hydraulic system. While DIY is possible for experienced enthusiasts, it's crucial to understand the process and safety implications. If you're unsure, always consult a professional mechanic.
Safety Precautions
Before you begin any work on your braking system, ensure your Subaru is safely parked on a level surface. Engage the parking brake, and use wheel chocks on the wheels that are not being worked on. Loosen the wheel nuts slightly before jacking up the vehicle, then securely support it on sturdy axle stands. Never rely solely on a jack.
Tools Required
You'll need a suitable jack and axle stands, a wheel brace, a spanner set (metric, typically 12mm, 14mm, 17mm, 19mm), a torque wrench, a brake piston compression tool (or a large C-clamp/prybar), high-temperature brake grease (silicone-based), a fluid drain pan, new brake fluid (matching your Subaru's specifications), a brake bleeding kit, and of course, your new brake pads and caliper.
Removing the Wheel and Old Components
- Remove the Wheel: Once the vehicle is safely on axle stands, fully remove the wheel.
- Access the Caliper: Locate the two guide pin bolts (sometimes called slider pins) on the back of the caliper. These typically have rubber boots covering them.
- Remove Caliper Bolts: Using the appropriate spanner, loosen and remove the guide pin bolts.
- Remove Old Caliper and Pads: Carefully slide the old caliper off the rotor. It will still be attached by the brake hose. Do not let it hang by the hose, as this can damage the line. Support it with a wire hanger or place it on a sturdy surface. Remove the old brake pads from the caliper bracket.
- Disconnect Brake Hose: Place your drain pan beneath the caliper to catch any dripping brake fluid. Using a flare nut spanner (to avoid rounding the fitting), carefully disconnect the brake hose from the old caliper. Be prepared for fluid to drip out. Quickly transfer the hose to the new caliper or plug it temporarily to minimise fluid loss and air entry.
Compressing the Caliper Piston (for pad replacement, or before installing a new caliper)
If you are only replacing pads, you will need to push the piston back into the caliper to make space for the thicker new pads. If installing a brand new caliper, this step is often not needed as new calipers typically come with the piston fully retracted.
For pad replacement:
- Using a Brake Piston Tool: The safest and most effective method is to use a dedicated brake piston compression tool. This tool typically screws or clamps the piston back evenly.
- Using a Prybar or C-Clamp: If you use a prybar, you must use an old brake pad to protect the piston and seal. Place the old pad against the piston face, then use the prybar to gently and evenly push the piston back into its bore. Be extremely careful not to damage the rubber boot or piston surface. As you push the piston back, brake fluid will be displaced back into the master cylinder reservoir. Keep an eye on the reservoir level and remove some fluid with a syringe if it's close to overflowing. This prevents spills and potential damage to painted surfaces, as brake fluid is corrosive.
Lubricating New Pads
This is a crucial step for preventing brake squeal after installation. Lubricate the backside of the new brake pads where they contact the caliper's piston and the caliper bracket's contact points. Use a high-temperature, silicone-based brake grease. Apply a thin, even coat. However, be extremely careful not to get grease on the pads' friction material or the rotor surface. Grease on the friction material will severely reduce braking performance and is incredibly dangerous. If any grease gets on the pad's surface, the pad must be replaced.
Installation of New Pads and Caliper
- Install New Pads: Carefully install the new brake pads into the caliper bracket. Ensure they are seated correctly and any anti-rattle clips are in place.
- Attach New Caliper: Connect the brake hose to the new caliper, ensuring the banjo bolt (if applicable) is tightened to the manufacturer's specified torque.
- Mount Caliper: Swing the new caliper over the rotor, ensuring the pads straddle the rotor correctly.
- Reinstall Guide Pin Bolts: Reinsert the guide pin bolts and tighten them to the specified torque. It's often recommended to apply a small amount of threadlocker to these bolts.
Brake Bleeding: Why It's Crucial
Whenever the hydraulic system is opened (as it is when replacing a caliper), air can enter the lines. Air in the brake lines is compressible, leading to a spongy brake pedal and significantly reduced braking effectiveness – a severe safety hazard. Therefore, bleeding the brakes is absolutely essential after a caliper replacement. This process involves forcing brake fluid through the lines to push out any trapped air bubbles.
- The Process: With the help of an assistant, you'll open the bleeder valve on the caliper, allow fluid (and air) to escape while your assistant slowly presses the brake pedal, then close the valve before they release the pedal. This is repeated until only clear, bubble-free fluid emerges. Always start with the caliper furthest from the master cylinder and work your way closer.
- Brake Fluid: Always use new, clean brake fluid of the correct DOT rating for your Subaru. Never reuse old fluid.
Final Checks and Bedding-In
Once everything is reassembled and bled:
- Pump the Pedal: Before starting the engine, pump the brake pedal several times until it feels firm. This seats the pads against the rotor and builds pressure in the system.
- Check Fluid Level: Top up the master cylinder reservoir with fresh brake fluid to the MAX line.
- Test Drive: Perform a careful test drive in a safe area. Start with gentle stops from low speeds, gradually increasing speed and braking force. This process, known as bedding-in, helps the new pads conform to the rotor surface, optimising performance and preventing noise. Avoid hard braking for the first 100-200 miles.
Brake Fluid: The Unsung Hero
Often overlooked, brake fluid plays a critical role in your braking system. It transmits the force from your foot on the pedal to the calipers. Brake fluid is hygroscopic, meaning it absorbs moisture over time, which lowers its boiling point and can lead to internal corrosion. Subaru recommends flushing and replacing brake fluid periodically, typically every 2-3 years, regardless of mileage. This preventative maintenance ensures consistent pedal feel and prolongs the life of your braking components.
Common Brake Issues and Troubleshooting
- Spongy Pedal: Most often indicates air in the brake lines, requiring bleeding. Could also be a fluid leak or master cylinder issue.
- Vehicle Pulling to One Side: Can be caused by a seized caliper on one side, unevenly worn pads, or a restriction in a brake line.
- Vibration During Braking: Commonly due to warped brake rotors, often caused by excessive heat or prolonged driving with worn pads.
- Excessive Brake Dust: Normal to some extent, but excessive dark dust can indicate aggressive pad material or heavy braking habits.
Frequently Asked Questions (FAQs)
Q1: How often should I check my Subaru's brakes?
It's advisable to have your Subaru's brakes inspected at least once a year or every 10,000 miles, whichever comes first. This is often done as part of your routine service or MOT. Regular visual checks for pad thickness and rotor condition can also be performed more frequently.
Q2: Can I replace just one brake pad?
No, brake pads should always be replaced in axle sets (i.e., both front pads or both rear pads). This ensures even braking force and prevents your vehicle from pulling to one side when you brake, which can be dangerous. Rotors should also be replaced or machined in pairs.
Q3: What are the signs of a faulty brake caliper?
Signs of a failing brake caliper include: your vehicle pulling to one side when braking, a burning smell (due to a seized caliper generating excessive heat), uneven brake pad wear (one pad significantly thinner than the other on the same wheel), fluid leaks around the caliper, or a noticeable decrease in braking performance on one side.
Q4: Is it safe to drive with worn brake pads?
Driving with worn brake pads is extremely dangerous. It compromises your vehicle's stopping ability, increases stopping distances, and can lead to complete brake failure. Furthermore, it can cause expensive damage to your brake rotors and calipers. Address worn pads immediately.
Q5: Do I need special tools for brake caliper replacement?
Yes, while some basic hand tools are sufficient for simple pad changes, a caliper replacement requires a few specific items. A brake piston compression tool is highly recommended for pushing back pistons. You'll also need a flare nut spanner for the brake line, a torque wrench for proper tightening, and a brake bleeding kit to remove air from the system after installation. Attempting the job without these tools can lead to damage or an unsafe braking system.
Maintaining your Subaru's braking system is not merely a matter of vehicle upkeep; it's a fundamental aspect of road safety. By understanding the signs of wear, choosing the right components, and following proper maintenance procedures, you can ensure your Subaru continues to offer the reliable, confident stopping power you expect. Whether you're tackling the job yourself or entrusting it to a professional, prioritising your brakes is an investment in your safety and peace of mind on every journey.
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