Wilwood GP310 4-Piston Brake Caliper – Front Left-Hand | Harley-Davidson 2008–Present | Black | 120-12117-BK

Wilwood 120-12117-BK GP310 4-piston billet aluminium brake caliper for 2008–present Harley-Davidson motorcycles. Front left-hand position, black anodised finish, direct fork leg mount — no brackets required. A significant performance and aesthetic upgrade over the OEM sliding single-piston caliper. 2.1 lbs. Ships fast across Canada and the US.

GP310 — Purpose-Built for Harley-Davidson

Wilwood’s GP310 is a motorcycle-specific caliper engineered for direct installation on 2008-and-newer Harley-Davidson Big Twin and Sportster models equipped with the leg-mount caliper bracket system. The GP310 uses Harley’s OEM caliper mounting boss locations on the fork leg — bolt-on installation without fabrication, custom brackets, or modification to the fork leg. Available for single disc models (one caliper) and dual disc models (L/H and R/H pair required).

4-Piston Fixed Caliper — Performance Upgrade

The OEM Harley-Davidson front brake caliper is a single-piston sliding design — functional for stock riding conditions but limited in braking force, modulation, and heat management for performance or heavily loaded riding. The Wilwood GP310 replaces this with a 4-piston fixed monoblock caliper:

• 4 pistons (2 per side): Even clamping force applied symmetrically across the brake pad face. Eliminates the uneven pad wear and flex inherent in sliding caliper designs. More consistent braking feel throughout the pad’s service life.
• Fixed monoblock design: The caliper body is one solid piece of billet aluminium — no flex between caliper halves under hard braking loads. Direct, immediate brake response.
• Greater braking force: Four pistons operating at the same hydraulic pressure as a single-piston OEM caliper generate significantly more total clamping force — shorter stopping distances and more consistent brake feel at higher speeds and loads.

Billet Aluminium Construction — Black Anodised

CNC-machined from solid 6061 billet aluminium — lighter than OEM iron or cast caliper designs and with superior heat dissipation characteristics. The black anodised finish is durable, corrosion-resistant, and provides a clean blacked-out aesthetic that suits most custom Harley builds. At 2.1 lbs, the GP310 is significantly lighter than a comparable iron caliper.

Piston and Rotor Specification

The GP310 120-12117-BK uses 1.25-inch diameter pistons and is designed for use with brake rotors of .25-inch (6.35mm) minimum thickness. Verify your front rotor meets the minimum thickness specification before installation — a rotor below minimum thickness combined with an upgraded caliper’s increased clamping force accelerates rotor wear and can cause rotor failure. Wilwood GP310-specific brake pads are required — source separately to complete the brake system upgrade.

Front Left-Hand — Dual Disc Buyers

This listing is the front left-hand caliper only (from the rider’s seated perspective). For single disc Harley models, one caliper covers the entire front brake. For dual disc models (where two rotors and two calipers are fitted to the front wheel), both a left-hand (120-12117-BK) and a right-hand caliper are required. Confirm your model’s front brake configuration before ordering.

Motorcycle brake component — safety-critical. Professional installation required. Full brake system bleed mandatory after installation. Pads and rotor not included. Left-hand caliper only — dual disc requires both sides.

Specifications

• Brand: Wilwood
• Part Number: 120-12117-BK
• Model: GP310
• Type: 4-piston fixed monoblock brake caliper
• Position: Front left-hand
• Piston diameter: 1.25"
• Minimum rotor thickness: .25"
• Finish: Black anodised
• Construction: Billet 6061 aluminium
• Mount: Direct fork leg mount
• Application: 2008–present Harley-Davidson (single and dual disc models)
• Weight: 2.1 lbs