KYB KG4539 Shock Absorber - Rear

KYB Gas-a-Just Rear Shock for BMW E30

The KYB Gas-a-Just KG4539 is a rear monotube shock absorber built for BMW 3 Series E30 applications. It is engineered as an OE-style replacement to restore original suspension response while adding firmer control for daily driving, heavier wheels, and demanding road conditions.

For BMW 318i, 318is, 325i, 325is, 325iX, 325e, and M3 rear suspension service, this KYB Gas-a-Just shock uses a high-pressure monotube design to separate gas and oil for consistent damping and quick response. The KG4539 is a direct-fit option for drivers looking for controlled ride quality on the BMW 3 Series platform.

Key Features

• Monotube shock absorber designed as an OE replacement for rear suspension service
• Up to 25% more damping performance than original equipment shocks
• High-pressure nitrogen gas and hydraulic working chambers for responsive control
• Triple chrome plated piston rod helps reduce seal wear and fluid leakage
• Built for BMW 3 Series E30 rear applications, including performance-oriented use
• Dust cover included; B-stop and R-stop included
• Lower mount type: E2(12X40); upper mount type: S1
• Compressed length: 13.7 in; extended length: 21.46 in; stroke length: 7.76 in

Product Details

The KYB Gas-a-Just line is a monotube shock absorber series focused on restoring OE ride characteristics with added damping reserve. In the KG4539, the separate gas and oil chambers help maintain fade-free operation and immediate shock response, which is important on the BMW 3 Series when suspension control and steering feel matter. This part number, KG4539, is also cross-referenced to Monroe Shocks & Struts 5947 for the same application.

Common Problems This Shock Can Address

• Excessive rear bounce after bumps or dips
• Reduced damping control from worn OE shocks
• Rear-end instability during braking or cornering
• Harsh response from tired suspension components
• Loss of steering precision caused by weak rear shock control

Installation Notes

Fits 1992 BMW 318i, rear; 1992 BMW 318is, rear; 1991 BMW 318i, rear; 1991 BMW 318is, rear; 1988-1991 BMW 325i, rear; 1988-1991 BMW 325is, rear; 1988-1991 BMW 325iX, rear; 1988-1991 BMW M3, rear; 1984-1987 BMW 325e, rear; and 1984-1985 BMW 318i, rear. For reduced noise and vibration, KYB recommends replacing the strut mount with part number SM5013. Verify mount style and suspension configuration before installation, especially on E30 models with noted exclusions such as M-Technik suspension.

Quality Assurance

KYB designs Gas-a-Just shocks with application-specific valving and OE-style fitment targets for BMW 3 Series rear suspension service. The monotube construction, high gas pressure, and chrome-plated rod are used to support consistent damping performance and long-term seal durability.