KYB KG5559 Suspension Shock Absorber - Rear

KYB Gas-a-just Rear Shock for Ford and Mercury

The KYB Gas-a-just KG5559 is a rear suspension shock absorber built for select Ford Mustang, Ford LTD, Mercury Capri, Mercury Marquis, Mercury Cougar, Ford Fairmont, and Mercury Zephyr applications. Its monotube design is made to deliver quicker response and more consistent damping than a traditional twin-tube shock, especially on vehicles with performance upgrades, towing demands, or larger wheels and tires.

Gas-a-just is KYB’s performance-oriented shock line, using a high-pressure monotube layout that separates gas and oil for stable operation. For rear suspension service on 1981-1993 Ford and Mercury models, this line is aimed at restoring control while adding firmer damping response where OE shocks can feel soft or fade under load.

Key Features

• Adds up to 25% more damping performance over original equipment shocks
• High-pressure monotube design separates gas and oil for fade-resistant operation and fast response
• Triple chrome plated piston rod helps reduce seal wear and fluid leakage
• Higher gas pressure improves steering response and suspension control
• Designed specifically for Ford and Mercury rear suspension applications
• Supports vehicles that work, tow, or run larger, heavier tires and wheels
• Dust cover included

Detailed Description

KYB KG5559 uses an air-free hydraulic working chamber for responsiveness and a separate high-pressure nitrogen chamber with a floating piston to maintain consistent damping. That construction helps the shock react quickly during normal driving and add control when the suspension is loaded harder. For rear suspension service on a Ford Mustang rear shock replacement or Mercury Capri rear shock upgrade, the Gas-a-just line is a direct-fit performance option focused on control, stability, and reduced fade.

This part cross-references Monroe Shocks & Struts 5847 for the same application.

What It Helps Solve

• Excessive rear bounce after bumps or dips
• Reduced control from worn OE-style shocks
• Fade during repeated suspension movement or heavier use
• Loose rear-end feel on Ford Mustang, Ford LTD, and Mercury applications
• Premature seal wear related to shock fluid leakage

Installation Notes and Tips

• Compatible with rear-position applications listed in the fitment data only.
• Verify compressed length, extended length, and mount types before installation: lower mount E2(12X53), upper mount S1.
• Inspect related suspension components such as bushings, springs, and mounting points during replacement.
• Use the vehicle’s service procedure for torque and alignment checks after installation.
• For 1983-1986 Mustang and Capri applications, confirm the notes regarding Special Handling Package exclusions.

Quality Assurance

KYB designs the Gas-a-just line with monotube construction and application-specific valving for Ford and Mercury rear suspension use. The KG5559 is engineered to maintain consistent damping response and support electronic safety systems that rely on the suspension operating as intended.

Fits 1981 Ford Fairmont, rear; fits 1981 Mercury Zephyr, rear; fits 1981-1982 Mercury Cougar, rear; fits 1982 Ford Mustang, rear; fits 1982 Ford Fairmont, rear; fits 1982 Mercury Capri, rear; fits 1982-1983 Ford Mustang, rear; fits 1982-1983 Mercury Zephyr, rear; fits 1983-1986 Ford LTD, rear; fits 1983-1986 Ford Mustang, rear; fits 1983-1986 Mercury Capri, rear; fits 1983-1986 Mercury Marquis, rear; fits 1987-1993 Ford Mustang, rear.