GMA Engineering Wagner Style Rear Master Cylinder 5/8 Bore for 1958-1979 Harley-Davidson FL FX

GMA Engineering Wagner Style Rear Master Cylinder 5/8 Bore for 1958-1979 Harley-Davidson FL FX

When a vintage Big Twin restoration calls for more than the stock system can deliver, the foundation of the upgrade starts at the master cylinder. The GMA Wagner gives riders of Panhead and Shovelhead-era machines the confident, firm pedal feel that transforms a period restoration into a bike built to be ridden — not just admired.

Key Features

• Reproduction of the original Wagner offset-mount design, CNC machined in the U.S.A. for direct installation on all 1958-early 1979 Big Twin frame locations without modification
• Correct offset mounting geometry for seamless integration with original Wagner-style brackets on FL and FX frames
• 5/8″ bore delivers the hydraulic volume required to properly actuate multi-piston aftermarket calipers without a spongy pedal feel
• Available in Natural, Polished, and Black finishes to suit any build style
• 1/8-27 NPT inlet compatible with standard hard-line brake fittings

Technical Specifications

• Bore Size: 5/8″
• Style: Wagner offset mount
• Inlet Size: 1/8-27 NPT
• Mounting Hole Diameter: 3/8″
• Mounting Hole Spacing: 2.25″ on center
• Mounting Offset: 3/8″
• Length: 4-1/16″
• Width: 1-7/16″
• Height: 2-7/8″
• Fluid Requirement: D.O.T. 5 Silicone Brake Fluid only
• OEM Cross-Reference: 41761-58 (1958-1972), 41761-78 (1973-1979)
• Manufacturing: Made in the U.S.A.

Fitment Notes

• All 1979 fitment applies to early production only; late 1979 models transitioned to the Kelsey Hayes inline mount — see Kelsey Hayes master cylinder listings
• Wagner offset mount is NOT interchangeable with Kelsey Hayes inline brackets — verify your mounting hole pattern before ordering
• Use D.O.T. 5 Silicone-based brake fluid only — do not mix with D.O.T. 3 or D.O.T. 4
• Mounting hardware not included
• Review the Fitment tab for the complete year and model breakdown