Alfa 105 Brake Upgrade: Alfetta Pedal Box Swap

For enthusiasts of classic Alfa Romeo 105 series cars, the joy of driving these iconic machines is often tempered by their original braking systems. While perfectly adequate for their era, modern traffic conditions and expectations for performance often highlight the limitations of a single-circuit, unboosted setup with standing pedals. The pursuit of enhanced safety, improved feel, and greater stopping power is a common and highly rewarding undertaking. This article delves into a comprehensive brake upgrade on an Alfa Romeo GT1300 Junior (105.31), detailing the ingenious integration of an Alfetta pedal box, Alfa 75 Twin Spark Brembo calipers, and a sophisticated adjustable proportioning valve, addressing the very real need for custom fabrication and careful re-routing.

The Drive for Better Braking: Why Upgrade?

The original Alfa 105 braking system, while robust for its time, presents several areas ripe for improvement. Primarily, many 105s feature a single-circuit master cylinder located under the floor. This design, while mechanically simple, offers no redundancy in the event of a hydraulic failure, which can lead to a complete loss of braking. Furthermore, the ‘standing’ pedal arrangement, where the pedals pivot from the floor, can feel less intuitive and offer less ergonomic advantage compared to modern ‘hanging’ pedal setups. The absence of a brake booster means a heavier pedal effort is required, and the solid, unventilated front discs, while effective, can be prone to fade under enthusiastic driving or repeated heavy use. Upgrading addresses these concerns, not just for performance but significantly for driver confidence and safety.

Integrating the Alfetta Pedal Box: A Foundation for Modern Braking

One of the most significant changes in this particular upgrade involves replacing the original 105 standing pedals and under-floor master cylinder with a right-hand drive (RHD) Alfetta pedal box assembly. This swap immediately transitions the car to a hanging pedal system, which many drivers find more ergonomic and precise. However, this isn't a direct bolt-on operation and requires considerable fabrication and careful adaptation.

Custom Fabrication: The Adaptor Plate and Firewall Modifications

The first step involves creating an adaptor plate from 8mm mild steel. This plate is custom-made to fit the driver's side (RHD) firewall of the 105. Its purpose is to provide a secure and correctly positioned mounting point for the Alfetta pedal box. The challenge doesn't stop there; the Alfetta pedal arms for both the brake and clutch require precise re-routing work. This is crucial to ensure they drop down cleanly on either side of the 105's steering column, allowing for full pedal travel without obstruction. This intricate modification highlights the necessity of careful measurement and skilled fabrication to ensure both functionality and safety.

Understanding the Alfetta Torsion Bar and Master Cylinder Integration

The Alfetta pedal box design includes a torsion bar. This bar runs from the pedal box itself, along the top of the firewall (situated between the rear of the engine and the scuttle at the base of the windscreen), to a dedicated bracket. This bracket is where the Alfetta's brake booster and dual circuit master cylinder assembly are mounted. The move to a dual circuit master cylinder is a massive safety upgrade, providing separate hydraulic lines for the front and rear brakes. Should one circuit fail, the other remains operational, preventing a complete loss of braking ability.

Addressing the Firewall Angle Discrepancy

A significant hurdle in this conversion is the difference in firewall geometry between the Alfetta and the 105. The Alfetta's firewall angles back towards the windscreen, whereas the 105's firewall is almost vertical. This means a direct mount of the Alfetta booster and master cylinder would leave them at an awkward, non-horizontal angle in the 105 engine bay. The solution involves fabricating a custom sub-bracket. This sub-bracket is designed to correctly orient the standard Alfetta booster bracket, bringing the booster and master cylinder into a perfectly horizontal position. This ensures optimal function and fluid flow, critical for a reliable braking system.

Front Brake Enhancement: Brembo Calipers and Ventilated Rotors

With the pedal box and master cylinder sorted, attention turns to the business end of the braking system. The chosen upgrade for the front brakes involves fitting a pair of Brembo calipers sourced from an Alfa 75 Twin Spark. These calipers are renowned for their superior clamping force and heat dissipation compared to the original 105 units.

Direct Fitment with Minor Adjustments

Remarkably, on a 1969 105 model, these Brembo calipers bolt straight onto the uprights, utilising the same bolt spacing as the original calipers. This 'plug and play' aspect (for the mounting holes at least) significantly simplifies the installation. However, some minor, yet crucial, modifications are still required:

• Rotor Dust Guard Trimming: The larger dimensions of the Brembo calipers necessitate slight trimming of the rotor dust guards to ensure adequate clearance. This prevents any rubbing or interference, which could compromise braking performance or damage components.
• Caliper Shimming: To prevent the disc rotor from rubbing on the inboard brake pad, 2mm shims must be installed between the caliper and the uprights. This precise spacing is vital for correct caliper alignment and even pad wear, ensuring optimal braking efficiency.

Upgrading to Ventilated Rotors

To complement the high-performance Brembo calipers, the original solid rotors are replaced with ventilated rotors. These new rotors, sourced from a knowledgeable supplier, are precisely dimensioned to match the 105's standard rotors, with one critical difference: they are 22mm thick to perfectly suit the Brembo calipers. Additionally, they feature a slightly larger diameter, approximately 5mm greater, which provides an increased swept area for better heat dissipation and stopping power. Ventilated rotors are crucial for sustained performance, as they allow air to circulate between the two disc faces, significantly reducing heat build-up and brake fade during heavy use.

Rear Brakes and the Adjustable Proportioning Valve

While the front brakes receive a substantial overhaul, the rear brakes are often left in their original configuration for such upgrades, assuming they are in good condition. The focus then shifts to managing the brake bias, which is where the proportioning valve comes into play.

The Role of the Proportioning Valve

A proportioning valve is a critical component in any modern braking system, especially when significant upgrades are made to one axle. Its function is to reduce the hydraulic pressure to the rear brakes relative to the front brakes during heavy braking. This prevents the rear wheels from locking up prematurely, which can lead to instability and loss of control, particularly in a front-heavy car under deceleration. The original 105 would have had a fixed proportioning valve, but with the upgraded front system, this balance needs to be carefully re-tuned.

Installing an Adjustable Proportioning Valve

The standard rear proportioning valve is removed and replaced with a 'knob style' adjustable proportioning valve, such as those offered by Wilwood or Tilton. This allows for precise, on-the-fly adjustment of the rear brake pressure, enabling the driver or technician to fine-tune the brake bias to suit driving conditions, tyre choice, or personal preference. This level of control is invaluable for optimising braking performance and stability.

Strategic Placement of the Valve

The placement of the new adjustable proportioning valve is a key consideration. It is installed on the firewall in the engine bay, tapped into the rear brake line after it leaves the master cylinder and before it disappears under the car. This location offers several advantages:

• Accessibility: Easy access for adjustments without needing to lift the car or delve into the cabin.
• Visibility: Allows for quick inspection of the valve and its connections.

Other potential locations, such as under the car near the original valve, were deemed inconvenient due to difficult access. Placing it inside the cabin, while offering even easier access, was dismissed due to potential concerns from Australian vehicle registration authorities for a road car, and the risk of curious passengers inadvertently altering the brake bias settings.

Comparative Table: Original vs. Upgraded Braking System

To better illustrate the scope and impact of this comprehensive upgrade, here's a comparison of key components and features:

Frequently Asked Questions About Alfa 105 Brake Upgrades

Is this type of brake upgrade a DIY job?

While some aspects of this upgrade might be tackled by an experienced DIY enthusiast, the custom fabrication, precise re-routing of pedal arms, and critical alignment of components (like the shimming for calipers) require significant skill, specialised tools, and a deep understanding of braking system mechanics. Given the safety-critical nature of brakes, it's highly recommended that such a comprehensive modification be undertaken by, or at least meticulously supervised by, a qualified and experienced automotive mechanic, ideally one with a specialisation in classic Alfa Romeos.

What are the legal implications of such modifications for a road car?

Vehicle modification regulations vary significantly by country and even by region within a country. In the UK, major modifications to braking systems require careful attention to ensure the vehicle remains roadworthy and passes its MOT (Ministry of Transport) test. It's crucial to consult with your local vehicle registration authorities or an approved vehicle inspection specialist before undertaking such extensive work. Features like dual-circuit braking and appropriate brake bias are generally viewed favourably, but non-standard components and custom fabrication must be professionally executed and certified if required. Placing an adjustable proportioning valve inside the cabin, for instance, might be scrutinised due to potential for tampering or accidental adjustment.

Are there other caliper options for the front brakes?

Yes, while Alfa 75 Twin Spark Brembos are an excellent choice due to their performance and relatively straightforward fitment, other options exist. These might include calipers from other Alfa models, aftermarket performance calipers from brands like Wilwood or AP Racing, or even custom big brake kits. Each option will come with its own set of challenges regarding mounting, rotor compatibility, and cost. The key is to ensure the chosen calipers are appropriate for the vehicle's weight and performance, and that they can be safely integrated with the rest of the braking system.

How important is brake fluid choice?

Extremely important! With a performance brake upgrade, especially one involving ventilated rotors and potentially higher operating temperatures, using a high-quality, high-boiling-point brake fluid (e.g., DOT 4 or DOT 5.1, but *not* DOT 5 silicone fluid unless the entire system is designed for it) is essential. Good brake fluid resists boiling, which can lead to a spongy pedal and loss of braking. Regular flushing and replacement of brake fluid are also crucial for maintaining optimal braking performance and longevity of components.

What's the main benefit of an adjustable proportioning valve over a fixed one?

The primary benefit of an adjustable proportioning valve is the ability to fine-tune the front-to-rear brake bias. A fixed valve provides a predetermined pressure split, which might be adequate for a stock setup but becomes less ideal when components are changed. An adjustable valve allows the driver or mechanic to compensate for changes in tyre grip, suspension settings, vehicle load, or even track conditions. This fine-tuning ensures that both front and rear brakes contribute optimally to stopping power without premature lock-up of either axle, leading to greater stability and shorter stopping distances.

Conclusion: A Rewarding Transformation

Undertaking a comprehensive brake upgrade like this on a classic Alfa Romeo 105 is a significant project, demanding meticulous planning, skilled fabrication, and a deep understanding of automotive mechanics. However, the rewards are substantial. The transformation from a traditional, single-circuit system with standing pedals to a modern, dual circuit, power-assisted setup with hanging pedals, Brembo calipers, ventilated rotors, and an adjustable proportioning valve fundamentally alters the driving experience. It not only provides vastly superior stopping power and resistance to fade but also instils a profound sense of confidence and safety, allowing the driver to fully enjoy the legendary dynamics of these cherished Italian classics on contemporary roads. The re-routing and custom work are indeed necessary, but the result is a beautifully integrated system that elevates the Alfa 105 to new levels of performance and driveability.

If you want to read more articles similar to Alfa 105 Brake Upgrade: Alfetta Pedal Box Swap, you can visit the Automotive category.