What Are the Components of a Fixed Caliper Brake Assembly?

A fixed caliper brake assembly consists of the caliper body (one- or two-piece), opposed pistons with square-cut seals and dust boots, internal fluid passages or crossover tubes and bleeder screws, brake pads with backing plates, shims and anti-rattle springs retained by pins or a bridge, caliper mounting ears/bolts and pad abutments, the hydraulic inlet hose/banjo, and the rotor/disc; many modern units also add pad wear sensors, heat shields, and splash shields. In practice, these parts work together to deliver rigid, even clamping on both sides of the rotor without the sliding hardware used in floating calipers.

Core caliper body and hydraulic components

The following parts make up the rigid housing and the hydraulic system that convert pedal pressure into clamping force in a fixed caliper design.

• Caliper body/bridge: A monobloc (one-piece) or two-piece bolted housing that spans the rotor and holds all working parts.
• Opposed pistons: Two or more pistons on each side of the rotor (common counts: 2, 4, 6, or 8 total) to apply even pressure.
• Piston seals: Square-cut internal seals that both seal fluid and provide piston retraction when pressure is released.
• Dust boots (external piston seals): Protective bellows that keep out debris and moisture.
• Internal fluid galleries and crossover passages/tubes: Internal drillings or external tubes that route fluid to pistons on both sides.
• Body half seals (two-piece calipers): O-rings or face seals that seal the fluid passages between caliper halves.
• Bleeder screw(s): One or more bleeders per side or chamber to purge air during service.
• Fluid inlet/port: Typically a banjo fitting or threaded port where the brake hose or hard line connects.
• Bridge bolts (two-piece) or structural bridge: Fasteners or a removable bridge bar that maintains caliper rigidity and, in some designs, also retains pads.

Together, these components form a rigid, hydraulically balanced unit that clamps the rotor from both sides with minimal flex for consistent pedal feel and stopping power.

Friction components and pad hardware

These parts contact the rotor and control noise, heat, and wear while transmitting hydraulic force into frictional braking.

• Brake pads (inner and outer): Friction material bonded or riveted to steel backing plates, matched to the rotor type.
• Pad shims/insulators: Layers that reduce noise and manage heat transfer from pads to pistons.
• Pad retaining pins/bolts or a pad-retaining bridge: Hardware that secures pads within the caliper window.
• Anti-rattle/return springs or spreader spring: Springs that stabilize pads and help prevent noise and drag.
• Pad wear indicators: Mechanical “squealer” tabs or electronic wear sensors integrated into the pad or harness.

This hardware ensures the pads are correctly located, quiet, and durable, while delivering uniform pressure to the rotor.

Mounting and interface hardware

Fixed calipers don’t slide; they are bolted solidly to the suspension and rely on precise interfaces to guide pad movement and align with the rotor.

• Caliper mounting ears/bores and bolts: Axial- or radial-mount fasteners that secure the caliper to the knuckle or dedicated bracket.
• Abutment surfaces or abutment plates: Hardened or stainless inserts where pad backing plates slide.
• Rotor/disc: Solid or vented steel/iron disc that the caliper clamps; integral to the overall brake assembly.
• Knuckle/hub interface: The mounting surfaces that maintain rotor-to-caliper alignment and wheel bearing geometry.

These elements keep the caliper rigidly located and provide the precise pad guides and braking surface required for consistent performance.

Hydraulic connection and protection

External lines and protective parts ensure reliable fluid delivery and help components survive heat, moisture, and debris.

• Brake hose or rigid line: Feeds hydraulic pressure to the caliper inlet; often flexible to accommodate steering/suspension movement.
• Banjo bolt and crush washers (if applicable): Seals the hose to the caliper port.
• Heat shields/thermal barriers: Protect pistons, boots, and fluid from rotor and pad heat (common on performance setups).
• Dust/splash shield (vehicle-dependent): A backing plate behind the rotor that helps keep contaminants away.

These parts safeguard braking reliability by preventing leaks and minimizing thermal or environmental damage.

How fixed calipers differ from floating calipers

Unlike floating calipers, which use slide pins and a single piston to pull the outboard pad against the rotor, fixed calipers are rigidly mounted and use opposing pistons to press both pads simultaneously. The design improves pedal feel, pressure distribution, and fade resistance, though it adds cost, weight, and complexity compared with typical sliding systems.

Current configurations and trends

Modern fixed calipers often feature multi-piston, monobloc construction for stiffness, internal crossover galleries to reduce external plumbing, and radial mounting for improved alignment and rigidity. Performance vehicles commonly employ 4-, 6-, or 8-piston designs, paired with vented rotors and high-temperature pad compounds.

Summary

A fixed caliper brake assembly comprises a rigid caliper body with opposed pistons, internal seals and fluid passages, bleeders and a fluid inlet; pads, shims, retaining pins and springs; rigid mounting ears with abutment surfaces; the rotor; and supporting hydraulic and protective hardware. Together, these components deliver precise, even clamping without the sliding hardware used in floating calipers, enabling consistent, high-performance braking.