15/07/2008
Few things are more grating to a classic car enthusiast than the incessant squeal of brakes. It's a common affliction, particularly with our beloved MGs, often leading to frustration and, as you've keenly observed, perhaps even a sense of embarrassment when pulling up to your own driveway. While the core function of brake calipers remains the same across different models – to clamp the brake pads onto the disc to create friction and slow the vehicle – there are crucial differences between the calipers found on an MG Midget and an MGB. Understanding these distinctions is the first step, but tackling the persistent squeal, especially with new components, requires a deeper dive into the mechanics of why these noises occur and how to effectively silence them.
The Core Differences: Midget vs. MGB Calipers
While both the Midget and the MGB are iconic British sports cars, their brake systems, specifically the front calipers, were designed for different vehicle weights, performance envelopes, and production eras. This means they are generally not interchangeable without significant modification.
Piston Size and Quantity
The most fundamental difference often lies in the piston size and, less commonly, the quantity. Early MG Midgets (MkI-MkIII) typically employed smaller Girling Type 14 calipers, which feature a single, relatively small piston. Later Midgets (MkIV and 1500 models) often upgraded to the Type 16P calipers, which are also single-piston but slightly larger and more robust. In contrast, the MGB, being a heavier and more powerful vehicle, almost exclusively used the larger Girling Type 16P calipers from its inception, featuring a single, larger piston designed to provide greater clamping force. The larger piston in the MGB caliper translates to more hydraulic force being applied to the pads, which is necessary to effectively slow down a heavier car.
Caliper Body and Mounting Bolt Patterns
Beyond the internal components, the physical dimensions and mounting bolt patterns of the caliper bodies are distinct. Midget calipers are generally more compact, designed to fit within the smaller wheel and suspension architecture of the car. MGB calipers are larger and feature a different bolt spacing and offset to accommodate the MGB's larger discs and steering knuckle. This difference in mounting is a primary reason why direct interchangeability is not possible. Attempting to fit an MGB caliper onto a Midget, or vice-versa, would require custom mounting brackets, which is not only impractical but also highly unsafe due to the critical nature of braking components.
Brake Pad Dimensions
Unsurprisingly, given the differences in caliper size and clamping force requirements, the brake pads themselves are also distinct. MGB brake pads are larger in surface area and typically thicker than those for an MG Midget. This larger surface area allows for better heat dissipation and greater friction, which is crucial for the MGB's performance demands. Using the incorrect pads for your caliper type will either result in them not fitting at all or, if forced, lead to dangerously compromised braking performance and potential component damage.
Performance Implications
The choice of caliper directly impacts the vehicle's braking performance. The MGB's larger calipers and pads are designed to provide superior stopping power and heat resistance compared to the Midget's setup. This is vital for a car that is heavier and capable of higher speeds. For instance, an MGB V8, as you've mentioned, places even greater demands on the braking system, necessitating robust MGB-spec components. Downgrading to Midget calipers on an MGB would severely compromise safety and performance, while upgrading a Midget with MGB calipers is a complex modification usually undertaken only for significant performance enhancements, involving changes to hubs, discs, and potentially the master cylinder.
Here's a brief comparative overview:
| Feature | MG Midget Caliper (Typical) | MGB Caliper (Typical) |
|---|---|---|
| Piston Type | Single Piston (Smaller) | Single Piston (Larger) |
| Caliper Body Size | More Compact | Larger, More Robust |
| Mounting Pattern | Specific to Midget Hub/Knuckle | Specific to MGB Hub/Knuckle |
| Brake Pad Size | Smaller Surface Area | Larger Surface Area |
| Primary Application | Lighter, Smaller MG Midget | Heavier, More Powerful MGB |
| Interchangeability | Not Direct | Not Direct |
Unravelling the Mystery of Persistent Brake Squeal
Your experience with persistent brake squeal, even after replacing calipers and trying various remedies, is remarkably common. The fact that it occurs with new components and returns after a few days of quiet points to a fundamental issue that's often overlooked. Brake squeal is, at its heart, a high-frequency vibration, a form of resonance. When the brake pad material rubs against the rotor, it creates friction, but if conditions are just right (or wrong!), this friction can set up a vibration that resonates through the caliper, hub, and suspension components, resulting in that tell-tale high-pitched noise.
The common culprits behind this unwelcome symphony typically include:
- Improper Lubrication: Not using the correct type of grease, or not applying it to the right contact points, allows metal-on-metal vibration.
- Pad Vibration: The brake pad itself vibrating within the caliper, often due to loose fitment or inadequate damping.
- Rotor Glazing or Warping: An uneven or overly smooth rotor surface can contribute to vibration.
- Poor Bedding-In: New pads and rotors (or calipers) need to be properly bedded-in to create an even transfer layer of friction material, which is crucial for quiet operation.
- Pad Material: Some pad compounds, especially performance-oriented ones, are inherently noisier due to their higher friction coefficients or metallic content.
- Caliper Issues: While less likely with new calipers, sticky pistons or worn caliper guide pins can cause uneven pad wear and vibration.
Your detailed attempts – greasing, chamfering, anti-squeal shims, and even considering CRC disc brake quiet – show a thorough approach. The fact that regreasing works for a few days, and the noise is particularly loud when pulling up outside your house (suggesting a specific brake temperature or gentle braking application), offers valuable clues. This points strongly towards issues with vibration damping and the initial bedding-in process of the new components.
Silencing the Squeal: A Comprehensive Troubleshooting Guide
Let's break down the solutions, building on your previous attempts and focusing on the nuances that often make the difference.
1. The Right Grease & Application
This is paramount. Standard chassis grease or general-purpose lubricants are simply not suitable for brake components due to the high temperatures involved. They can break down, lose their effectiveness, or even contaminate the brake pads. You need a dedicated, high-temperature brake lubricant. Look for products specifically labelled as 'brake grease', often containing copper (copper grease) or silicone (synthetic brake grease). These are designed to withstand extreme heat and provide long-lasting lubrication.
Where to apply it:
- Backing Plates: A thin, even layer on the metal backing plate of the brake pad where it contacts the caliper pistons and the caliper body.
- Caliper Contact Points: Where the brake pad ears slide into the caliper's abutment clips or machined surfaces.
- Guide Pins/Slides: If your calipers use guide pins (often found on floating caliper designs, though less common on the fixed Girling calipers of MGs, but still relevant if parts slide), ensure these are clean and lightly greased.
- Anti-Squeal Shims: If using metal shims, a thin layer between the shim and the pad backing plate, and between the shim and the caliper piston/body.
Crucially, ensure absolutely no grease gets onto the friction material of the pad or the rotor surface. Even a tiny amount can cause significant braking issues and more noise.
2. Anti-Squeal Shims: The Unsung Heroes
You mentioned replacing metal shims with self-adhesive ones and even using offcuts. Shims are designed to damp vibrations and provide a barrier between the pad backing plate and the caliper. They essentially act as a cushion. Metal shims often have rubber or composite layers bonded to them for this purpose. Self-adhesive shims (often a viscoelastic material) work by absorbing kinetic energy and converting it into heat, thus reducing vibration.
Ensure the shims are correctly fitted and cover the entire contact area. If using adhesive shims, the surface must be meticulously clean and dry for proper adhesion. The "offcuts on leading and trailing edges" is an interesting approach, aiming to address specific points of vibration, but a full, correctly fitted shim that covers the entire back of the pad is usually more effective for overall damping.
3. Chamfering and Scoring Pads
Chamfering the edges of the brake pads (grinding a slight angle off the top and bottom edges) helps by preventing the leading edge of the pad from 'grabbing' the rotor and initiating vibration. Scoring (cutting a shallow groove down the centre of the pad) can also help to break up the surface area and provide a path for dust and gasses to escape, which can reduce noise. You've correctly identified these as valid techniques, and they can certainly contribute to quieter operation, especially when combined with other methods.
4. The Crucial Step: Proper Bedding-In
This is often the most overlooked step, especially when new calipers and pads are fitted. Bedding-in (sometimes called 'burnishing') is the process of transferring an even layer of friction material from the brake pads onto the brake rotors. This transfer layer is essential for optimal braking performance and, critically, for quiet operation. Without proper bedding-in, the pads and rotors won't mate correctly, leading to uneven contact, hot spots, and, you guessed it, squeal.
Bedding-in Procedure (General Guide):
- Find a safe, unpopulated road where you can safely perform multiple stops without interruption.
- Accelerate to about 30-40 mph (approx. 50-65 km/h).
- Apply the brakes moderately (not hard, but firmly enough to slow the car significantly) down to about 5-10 mph (approx. 8-16 km/h). Do *not* come to a complete stop.
- Immediately release the brakes and accelerate back up to 30-40 mph.
- Repeat this process 8-10 times. You might start to smell the pads, which is normal.
- After the last stop, drive for several minutes without using the brakes much, allowing them to cool down. Do not hold the brake pedal down while stopped immediately after the bedding process, as this can imprint pad material onto the hot rotor, leading to pulsation and noise.
- Let the brakes cool completely to ambient temperature before normal driving. This might take an hour or more.
This process creates that vital, even transfer layer, which greatly reduces the likelihood of vibration and squeal. The fact that your squeal returns after a few days suggests this layer might not be forming or adhering correctly, or it's being unevenly worn away.
5. Rotor Condition and Pad Quality
Even with new calipers and pads, the rotors play a significant role. If your existing rotors are glazed (have a hard, shiny surface), warped, or have significant scoring, they can contribute to squeal. Ideally, when fitting new pads and calipers, new rotors should also be installed to ensure perfectly matched friction surfaces. If reusing rotors, they should be inspected for run-out and potentially skimmed (machined) to provide a fresh, flat surface.
The quality of the brake pads also matters. Cheaper, lower-quality pads may use compounds more prone to noise, or their backing plates may not be as precisely manufactured, leading to poor fitment within the caliper. For a V8, ensuring you have pads designed for the higher demands is even more critical.
6. Caliper Health (Even New Ones)
While you've fitted new calipers, it's worth a quick check. Ensure they are correctly mounted and torqued to specification. Confirm that the pads are able to slide freely within the caliper without excessive play or binding. Even new components can sometimes have manufacturing tolerances that lead to a less-than-perfect fit.
7. The "V8" Context
Your mention of the V8 is key. An MGB V8 would typically utilise the standard MGB calipers, but the increased power and weight demand that these components are in peak condition and correctly installed. The principles of silencing squeal remain the same, but the forces involved are greater, making proper bedding-in and high-quality components even more critical.
The CRC Disc Brake Quiet you've acquired is a viscous liquid applied to the back of the pads. It works by creating a damping layer that absorbs vibrations, similar to shims. Given your persistent issue, it's certainly worth trying, ensuring you apply it cleanly and allow it to cure as per the manufacturer's instructions. It might be the final piece of the puzzle to dampen those specific resonant frequencies that are causing your neighbourhood's impromptu concert.
Frequently Asked Questions
Q: Can I put MGB calipers on an MG Midget for better braking?
A: Not directly. MGB calipers are larger and have different mounting bolt patterns. Swapping them would require significant and complex modifications to the Midget's hubs, steering knuckles, and potentially the brake lines and master cylinder. It's generally not a straightforward or recommended upgrade for the average enthusiast.
Q: Why do my brakes squeal only when cold, or only when hot?
A: Squealing when cold often indicates a lack of proper bedding-in or issues with pad material that hasn't reached its optimal operating temperature. Squealing when hot, or after sustained braking, can suggest pad glazing, rotor issues, or the brake system reaching temperatures where lubrication breaks down or components expand unevenly, leading to new resonant frequencies.
Q: Is it safe to drive with squealing brakes?
A: While annoying, squealing brakes aren't always a sign of immediate danger if the car is still stopping effectively. However, it indicates a problem that should be addressed. Persistent squealing can be a symptom of worn pads, glazed rotors, or other issues that could eventually compromise braking performance. It's always best to investigate and resolve the cause to ensure maximum safety.
Q: How often should I re-grease my brake pads?
A: Ideally, brake components should be cleaned and re-greased during every pad change or at least during annual brake inspections. The longevity of the grease depends on the type used and driving conditions, but regular maintenance ensures optimal performance and quiet operation.
Q: Can worn suspension components cause brake squeal?
A: Indirectly, yes. Worn wheel bearings, control arm bushes, or ball joints can introduce excessive play or vibration into the wheel assembly, which can then be transmitted to the braking system and exacerbate or even cause squeal. Ensuring your suspension is in good order is part of comprehensive brake maintenance.
Conclusion
Understanding the fundamental differences between Midget and MGB brake calipers is crucial for correct parts selection and maintenance. While the initial problem might seem like a simple parts swap, the persistent squeal you're experiencing, especially with new components, points to the nuances of brake system harmony. The key to silencing that annoying squeal lies in a meticulous approach to lubrication with the correct high-temperature grease, ensuring proper anti-squeal shim installation, and, most critically, performing a thorough bedding-in procedure for your new pads and calipers. Persistence pays off; with the right techniques, your classic MG will soon be stopping as quietly as it runs, restoring the joy of driving without the unwanted soundtrack.
If you want to read more articles similar to Midget vs. MGB Calipers: Silencing the Squeal, you can visit the Brakes category.