Disassembling Avid BB7 & BB5 Brakes

The Avid BB7 and BB5 mechanical disc brakes have been a staple for many cyclists, particularly those looking for reliable and adjustable stopping power without the complexity and cost of hydraulic systems. While generally robust, these brakes can sometimes require a bit of attention, whether it's due to seized adjusters, general wear and tear, or simply a desire for a thorough overhaul. Disassembling these brakes, while not overly complex, does have a few specific points to be aware of. This guide will walk you through the process, focusing on common issues and best practices, drawing from practical experience to help you keep your Avid brakes performing at their best.

Understanding the BB7 and BB5 Mechanisms

Before diving into disassembly, it's helpful to understand the core components and how they function. Both the BB7 and BB5 utilise a ball ramp mechanism to actuate the moving brake pad. The brake lever pulls a cable, which moves an actuator arm. This arm rotates a cam, pushing ball bearings against a ramp. The ramp, in turn, pushes the moving pad towards the rotor. The key differences lie in the adjustment mechanisms and some internal details.

The BB7 is known for its independent pad adjustment (Tri-Align) and a robust design. The BB5 is a slightly simpler, often more budget-friendly option. A common issue across both, particularly in adverse weather conditions, is the seizing of the Fixed Pad Adjuster (FPA). This adjuster, often a grub screw, allows you to fine-tune the position of the stationary pad. When it seizes, it can make pad wear adjustments difficult, and in severe cases, prevent proper brake function.

Tackling the Seized Fixed Pad Adjuster (FPA)

This is arguably the most common hurdle when overhauling Avid mechanical discs. Salt, water, and grit can wreak havoc on the threads of the FPA and the caliper body. Here’s how to approach it:

Initial Attempts:

• Finger Power: Always try to use finger pressure first. If it won't budge, don't force it too hard with a tool immediately.
• Torx Key: The FPA typically has a Torx head. Use the correct size Torx key. If it starts to round out, stop.

Escalating the Approach:

• Removing the Knob: If the Torx head is damaged or the adjuster is severely stuck, removing the FPA knob can provide better access. This often involves carefully prying out the knob with a small, thin screwdriver (like a jeweller's screwdriver). Once the knob is off, you might be able to get an 8mm socket onto the back of the FPA screw itself.
• Penetrating Oil & Heat: Apply a good quality penetrating oil (like WD-40 or a dedicated rust penetrant) and allow it ample time to work. Gentle heat from a heat gun (avoiding excessive heat which can damage seals or the caliper body) can also help expand the metal and break the corrosion bond. Tapping the area around the FPA with a small hammer can also help vibrate the threads loose.
• Using a Drift: If the FPA is still stubborn, a hollow drift that fits over the FPA screw's protruding end can be used with a hammer to try and shock it loose.

Cleaning the Threads:

Once the FPA is out, or if you're trying to clear seized threads within the caliper body, use a pointed tool (like a pick or a small dental tool) to meticulously clean out any corrosion or grit from the threads in the caliper body. Ensure all debris is removed.

Reassembly and Adjustment of the FPA

When refitting the FPA, a small smear of copper grease or a suitable anti-seize compound on the screw threads can significantly help prevent future seizing. Don’t over-tighten.

Setting the Initial Clearance:

A good way to check if the threads are sufficiently clean and the FPA is working is to install new pads (or the old ones if they aren't too worn) into a loose caliper. With the Moving Pad Adjuster (MPA) on the BB7 backed out, you should be able to wind the FPA in until the clearance between the pads and the rotor is almost zero. If you can't achieve this minimal clearance, the threads likely still have some obstruction.

Disassembling the Brake Arm and Mechanism

Once the FPA is dealt with, you can proceed with the main disassembly of the brake arm and the internal mechanism.

Avid BB7 Disassembly:

1. Remove the Moving Pad Adjuster (MPA): On the BB7, the MPA knob simply pops off. You can usually pry it off with a thin screwdriver.
2. Accessing the Mechanism: The core of the brake mechanism, including the ball ramp, sits within the caliper body. The most common way to access this is by removing the brake arm. The brake arm is usually secured by a bolt that passes through the caliper body and into the arm.
3. The Caliper Split (Less Common): In some cases, the caliper body itself might be split into two halves for a more thorough overhaul. This is less common for routine maintenance and usually reserved for deep cleaning or if significant wear is suspected in the caliper body itself.

Avid BB5 Disassembly:

1. Plastic Cover: The BB5 has a plastic cover on the brake arm. This usually pops off with a jeweller's screwdriver.
2. The Bi-Hex Bolt: This is where the BB5 introduces a unique challenge. The bolt securing the caliper arm has a bi-hex (12-point) head, not a standard hex or Torx. You will need a matching 12-point socket or ring spanner. An 8mm bi-hex tool is typically required.
3. Accessing the Recess: The trick with the BB5 is often the orientation of the spanner. The caliper arm has a small recess designed to "time" the plastic cover. If you orient an 8mm bi-hex ring spanner correctly, the shank of the spanner can sit within this recess, allowing it to fit over the bolt head even though the bolt sits in its own recess. If this doesn't work, you'll need a thin-walled 8mm bi-hex socket.
4. Threadlocker: When refitting this bolt, applying a small amount of threadlocker (like blue Loctite) is a good idea to prevent it from vibrating loose.

Internal Components and Maintenance

With the brake arm removed, you'll have access to the ball ramp mechanism.

• Greasing: Apply a small amount of non-melting, non-separating grease to the ramp surfaces and the balls themselves. This ensures smooth operation and protects against corrosion.
• Ball Bearings: The 7/32" ball bearings can be replaced if they are damaged or lost. Ensure you have the correct size.
• Wear: Inspect the caliper body bore where the moving cam and pads slide. Signs of scoring or deep grooves indicate wear. Similarly, check the brake arm for wear where the cam rotates. If the caliper body bore is significantly worn, the moving pad may not return square to the rotor, leading to brake rub.

Common Issues and Solutions

Several factors can lead to poor performance, even after a successful disassembly and reassembly:

• Pad Springs: Ensure the pad springs are correctly installed and providing adequate tension to retract the pads. Weak or incorrectly fitted springs can cause pads to cock slightly.
• Pad Binding: If the pads are binding in the caliper body bore, it can prevent smooth movement. Cleaning the bore and ensuring no burrs or debris are present is crucial.
• Back Plate Articulation: The back plate behind the moving pad can wear, allowing the pad to sit at an angle. If this back plate is excessively loose or worn, it can contribute to pad cocking. Finding a robust solution for badly worn calipers can be challenging.

Understanding Pad Clearance and Adjustments

A key feature of Avid BB7s (and to some extent BB5s) is the ability to set pad clearance accurately. The FPA thread pitch is typically 1mm, and a full stroke of the brake lever moves the pad about 1mm. This allows for very fine adjustments.

Marker Pen Marks:

• FPA Wheel: Put a marker pen line on the FPA wheel and a corresponding mark on the caliper body. This helps you track your adjustments and return to a known setting if needed.
• BB5 Road Caliper Mark: For BB5 'road' calipers, it's particularly important to mark the caliper body to indicate when the brake arm is approaching the end of its travel. BB5 road variants have less travel than their MTB or BB7 counterparts. Running out of travel can lead to a sudden and complete loss of braking.

Proper Adjustment:

If set up correctly, the moving pad should only need to be worn by about 1.75mm before pads are due for replacement. However, if the cable tension is used as the *only* means of adjustment and the FPA is neglected, the brake arm can run out of travel prematurely, even with plenty of pad material left. Always use the FPA to set the pad clearance, and only use cable tension to take up slack.

Table: BB7 vs. BB5 Key Differences

Frequently Asked Questions

Q1: How do I know if my Avid BB7/BB5 brakes need a full overhaul?

If you're experiencing increased lever travel, inconsistent braking, difficulty adjusting pad wear using the FPA, or if the brakes feel "spongy" or weak, it's a good time to consider an overhaul. Also, if the bike has been exposed to wet or salty conditions for extended periods, corrosion can build up.

Q2: Can I use regular grease on the ball ramp mechanism?

It's best to use a grease that is specifically designed not to separate or melt under moderate heat. Standard automotive greases might work, but a bicycle-specific grease or a light silicone grease is ideal for the ball ramp mechanism to ensure smooth, consistent operation.

Q3: My FPA is completely seized, what else can I try?

If penetrating oil, heat, and careful application of force haven't worked, you might consider professional help. A bike shop may have more specialised tools or techniques. In extreme cases, the caliper body might need to be replaced.

Q4: How often should I overhaul my Avid mechanical disc brakes?

For most riders, a thorough clean and re-grease of the mechanism every 6-12 months, or at least once a year, is beneficial. If you ride frequently in harsh conditions (rain, mud, salt), more frequent checks and maintenance are recommended. Overhauling when you change brake pads is a good routine.

Q5: What tools do I absolutely need for this job?

You'll need a set of Torx keys (T25 is common for many brake components, but check your specific FPA), a small jeweller's screwdriver set, an 8mm socket or ring spanner (and potentially a thin-walled version for the BB5 bi-hex bolt), possibly a 12-point 8mm socket/spanner for the BB5, a pick or thin pointed tool for cleaning threads, and appropriate grease and cleaning supplies.