31/03/2019
When undertaking brake maintenance or replacement, particularly on vehicles equipped with disc brakes, you'll inevitably encounter the need to compress the brake caliper piston back into its housing. This is a crucial step to allow for the removal of the old brake pads and the installation of new ones. While some pistons can be pushed back with a sturdy screwdriver or a C-clamp, many modern vehicles, especially those with “screw-in” type pistons found on many rear calipers and some front calipers, require a specific tool to rotate the piston back into the caliper body. This is where a brake caliper rewind kit, also commonly known as a brake piston rewind tool or brake caliper compression tool, comes into play. These kits are designed to make this often fiddly job significantly easier and more importantly, prevent damage to the caliper and its seals.
What Exactly is a Brake Caliper Rewind Kit?
A brake caliper rewind kit is a specialised set of tools designed to safely retract the brake caliper piston. Unlike simple compression tools that just push the piston straight back, rewind kits incorporate a mechanism that rotates the piston as it is pushed inwards. This rotation is essential for pistons that have a threaded shaft that needs to be screwed back into the caliper body. Think of it like winding a screw; you're not just applying force, but also rotational movement. This process is vital for ensuring the new brake pads can be fitted correctly and that the braking system functions as intended.
Why Do You Need a Rewind Kit?
The primary reason for needing a brake caliper rewind kit is the design of certain brake caliper pistons. Many vehicles, especially those with rear disc brakes, employ a piston that requires rotation to retract. This is often linked to the parking brake mechanism, which is sometimes integrated into the caliper itself. When you engage the parking brake, a mechanism within the caliper pushes the piston out against the brake pad. To retract this piston for pad replacement, you need to reverse this process by screwing it back in. Attempting to force a screw-in piston without the correct tool can lead to:
- Damage to the piston seals: Forcing the piston can tear or damage the delicate seals, leading to brake fluid leaks and a loss of braking performance.
- Damage to the caliper body: Excessive force can warp or crack the caliper housing.
- Damage to the master cylinder or brake fluid reservoir: If you try to push the fluid back without retracting the piston, you can over-pressurise the system, potentially damaging the master cylinder or causing the reservoir to overflow.
- Incorrect installation of new pads: If the piston isn't fully retracted, you won't be able to fit the new, thicker brake pads, leading to a frustrating and incomplete job.
A rewind kit ensures that the piston is retracted smoothly and correctly, preserving the integrity of the braking system and making the job much more straightforward. They are an indispensable item for any DIY mechanic or even professional garages that frequently work on a variety of vehicles.
Components of a Typical Brake Caliper Rewind Kit
While kits can vary slightly in their exact contents, most comprehensive brake caliper rewind kits will include:
The Rewind Tool
This is the core of the kit. It typically consists of a handle that you turn, connected to a mechanism that engages with the piston. This mechanism usually involves a spindle with a rotating disc or adaptor at the end. The kit will come with a selection of different adaptors or "discs" that have various pin configurations. These adaptors are designed to fit into the notches or splines on the face of the brake caliper piston, allowing you to grip and rotate it.
Interchangeable Adaptors/Discs
As mentioned, a good kit will provide a range of adaptors to suit different caliper piston designs. These adaptors typically have 2-pin, 3-pin, or 4-pin configurations, with varying distances between the pins. It's crucial to select the correct adaptor that fits snugly into the piston's grooves without damaging them. Common adaptors include:
| Adaptor Type | Typical Use | Key Features |
|---|---|---|
| 2-Pin Disc | Many European and Japanese vehicles (e.g., Volkswagen, Audi, Ford, Honda) | Pins set at specific distances to engage piston slots. |
| 3-Pin Disc | Some specific models, often with larger calipers. | Wider spread of pins for different piston designs. |
| 4-Pin Disc | Common on some American vehicles (e.g., Chrysler, Dodge, some GM models). | Often used for pistons that require a more robust engagement. |
| Specialised Adaptors | Certain specific vehicle makes/models (e.g., Ford Transit, some Mercedes-Benz). | Unique pin arrangements or magnetic attachments. |
Magnetic Plate/Holder
Many kits include a magnetic plate or a holder for the adaptors. This is incredibly useful for keeping the various discs organised and readily accessible when you're working in a dirty environment like a garage. It also helps prevent them from getting lost.
Carry Case
A sturdy, organised carry case is standard with most kits. This protects the tools from damage and makes storage and transport much easier.
How to Use a Brake Caliper Rewind Kit
Using a rewind kit is a relatively straightforward process, but it requires care and attention to detail. Here's a general step-by-step guide:
- Safety First: Ensure the vehicle is on a level surface, the parking brake is disengaged (unless working on the rear brakes where the parking brake might be integrated), and the ignition is off. Chock the wheels that are not being worked on. Wear safety glasses and gloves.
- Remove the Wheel: Loosen and remove the lug nuts and take off the wheel.
- Remove the Brake Pads: You'll typically need to remove the caliper retaining pins or bolts to slide the caliper off the rotor. Once the caliper is off, you can remove the old brake pads. Sometimes, you might need to gently pry the old pads out.
- Select the Correct Adaptor: Examine the caliper piston. Identify the notches or splines on its face. Choose the adaptor from your kit that best fits these notches. It should engage firmly without wobbling.
- Attach the Rewind Tool: Fit the selected adaptor onto the spindle of the rewind tool.
- Retract the Piston: Place the adaptor onto the caliper piston, ensuring the pins align with the piston's slots. Rotate the handle of the rewind tool clockwise. You should feel the piston slowly screwing back into the caliper body. Continue rotating until the piston is fully retracted, flush with the caliper housing. Do not force it; if it feels excessively tight, double-check that you have the correct adaptor and that there's no debris obstructing the piston.
- Check Brake Fluid Level: As you retract the piston, the brake fluid level in the reservoir will rise. Keep an eye on it and be prepared to remove some fluid if it threatens to overflow. It's also a good opportunity to inspect the fluid for contamination.
- Install New Pads: With the piston retracted, you can now install the new brake pads. They should slide into place easily.
- Reassemble the Caliper: Re-fit the caliper over the new pads and rotor, and secure it with the retaining pins or bolts.
- Repeat for Other Wheels: Follow the same procedure for the other side of the axle, and for any other wheels requiring brake pad replacement.
- Pump the Brakes: Before driving the vehicle, sit in the driver's seat and pump the brake pedal several times until it feels firm. This is crucial to push the newly retracted pistons back out against the new pads.
- Final Checks: Re-check the brake fluid level and top it up if necessary with the correct type of brake fluid. Ensure all lug nuts are tightened to the manufacturer's recommended torque.
Choosing the Right Kit
When purchasing a brake caliper rewind kit, consider the following:
- Vehicle Compatibility: While most kits are fairly universal, some specialised kits cater to specific makes or models. Check the kit's specifications for compatibility with your vehicle.
- Number and Variety of Adaptors: A kit with a wider range of adaptors will be more versatile and useful for a broader spectrum of vehicles.
- Build Quality: Look for kits made from durable materials like hardened steel for the adaptors and sturdy plastic or metal for the tool body. This ensures longevity and reliability.
- Ease of Use: Some designs are more ergonomic than others. Read reviews to gauge how easy the tool is to handle and operate.
- Price: Kits can range from budget-friendly options to more expensive professional sets. Balance cost with the quality and features offered.
Common Pitfalls and Tips
Even with the right tools, brake work can present challenges. Here are some common pitfalls and tips:
- Incorrect Adaptor: Using the wrong adaptor is the most common mistake. Ensure a secure fit before rotating.
- Overfilling Reservoir: Always monitor the brake fluid reservoir.
- Not Pumping Brakes: Forgetting to pump the brake pedal before driving is dangerous.
- Seized Pistons: Occasionally, a piston may be severely seized. In such cases, the caliper might need rebuilding or replacing, rather than just a rewind.
- Lubrication: While retracting the piston, ensure the caliper slide pins are lubricated when reassembling.
- Torque Wrench: Always use a torque wrench for caliper bolts and lug nuts.
Frequently Asked Questions
Q1: Do all brake calipers need a rewind tool?
No, only those with pistons that require rotation to retract. Many older or simpler front calipers can be compressed with a C-clamp or a simple push-rod tool. However, rear calipers often feature screw-in pistons, and many modern front calipers on performance vehicles also use this design.
Q2: Can I use a regular C-clamp to rewind a screw-in piston?
No, a C-clamp will only push the piston. It cannot provide the necessary rotational force to screw in a threaded piston. Attempting to do so will likely cause damage.
Q3: What happens if I don't retract the piston enough?
If the piston is not fully retracted, the new brake pads will not fit. You will not be able to slide the caliper back over the rotor.
Q4: How do I know which adaptor to use?
Visually inspect the face of the piston. It will have slots or notches. Match these to the pins on the adaptors. Try fitting each one gently until you find the one that engages securely.
Q5: Is it safe to reuse old brake fluid?
It's generally not recommended. Brake fluid absorbs moisture over time, which lowers its boiling point and can lead to corrosion. If you remove fluid from the reservoir, it's best to discard it properly and top up with fresh fluid.
In conclusion, a brake caliper rewind kit is a specialised but essential tool for anyone performing brake pad replacement on vehicles with screw-in type caliper pistons. By understanding its function and using it correctly, you can ensure a safe and successful brake maintenance job, protecting your vehicle's braking system and saving yourself potential costly repairs.
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