Custom Chrome Rear Master Cylinder Kelsey Hayes 5/8 Bore for 1979-1984 Harley-Davidson FL FX XL

Custom Chrome Rear Master Cylinder Kelsey Hayes 5/8 Bore for 1979-1984 Harley-Davidson FL FX XL

For builders pairing a multi-piston caliper with a Shovelhead frame, the braking equation only works when the master cylinder can keep up. This Custom Chrome reproduction puts the hydraulic authority behind every stop to match the caliper upgrade — giving the custom build the firm, predictable pedal feel the rest of the braking system is asking for.

Key Features

• Reproduction of the original Kelsey Hayes design for correct mounting geometry and period-correct appearance
• Accepts 3/8-24 inverted flare or 10mm banjo bolt brake line fittings — verify your brake line fitting type before ordering
• Correct 5/16″ mounting holes on 2.25″ centers bolt directly to OEM bracket spacing without modification
• Replaces OEM part numbers 42453-80A and 42454-80A

Technical Specifications

• Bore Size: 5/8″
• Inlet Size: 3/8-24 or 10mm banjo bolt
• Mounting Hole Diameter: 5/16″
• Mounting Hole Spacing: 2.25″ on center
• Length: 4″
• Width: 1.5″
• Height: 3.125″
• Construction: Chrome-plated cast aluminum
• Fluid Requirement: D.O.T. 5 Silicone Brake Fluid only
• OEM Cross-Reference: 42453-80A, 42454-80A

Fitment Notes

• All 1979 fitment applies to late production only; early 1979 models using a Wagner-style offset mount are not compatible
• 5/8″ bore is required for multi-piston aftermarket calipers; use a 3/4″ bore unit for stock single-piston calipers
• Inlet accepts 3/8-24 inverted flare or 10mm banjo bolt — not compatible with 1/8-27 NPT hard line fittings
• Use D.O.T. 5 Silicone-based brake fluid only — do not mix with D.O.T. 3 or D.O.T. 4
• Review the Fitment tab for the complete year and model breakdown