1999 Chrysler 300M Recommended Suspension Upgrade Parts

The 1999 Chrysler 300M was a standout sedan with a sporty character and a comfortable ride. Two decades later, the original suspension components are likely worn, leading to floaty handling, excessive body roll, and a harsh ride. Upgrading the suspension not only restores the driving experience but can improve it significantly. This guide covers the essential parts to consider and how to choose what’s right for your driving style and budget.

Why Upgrade the Suspension on a 1999 Chrysler 300M?

A vehicle’s suspension system is responsible for ride comfort, handling, and tire grip. Over time, springs sag, shocks lose damping ability, and bushings crack. The 300M is no exception. Upgrading addresses common issues and unlocks better performance.

Common Issues

• Worn struts and shocks: The factory units may be leaking or have lost damping, causing a bouncy ride and poor control.
• Sagging rear springs: Many 300Ms sit lower in the rear, leading to a nose-high stance and reduced stability.
• Loose steering and body roll: Age-weakened sway bar bushings and end links allow excessive chassis lean in corners.
• Noise and vibration: Deteriorated control arm bushings and strut mounts transmit road imperfections into the cabin.

Benefits of Upgrading

• Improved handling: Tighter cornering, less body roll, and better steering response.
• Ride quality: Modern dampers and bushings can provide a controlled, compliant ride without harshness.
• Longevity: Quality aftermarket parts often outlast factory components and resist wear better.
• Customization: Choose between a comfort-oriented setup or a sportier feel.

Key Suspension Components to Upgrade

Struts and Shocks

The 300M uses a strut-type front suspension and a separate shock absorber in the rear. Replacing these is the single most impactful upgrade.

• KYB Excel-G: A direct replacement that offers a smooth ride very close to OEM. Good for daily drivers who want predictable handling without harshness.
• Monroe OESpectrum: Similar to KYB, with a focus on comfort. These are affordable and widely available.
• Bilstein B6: A major step up in damping control. These are gas-charged and provide excellent stability at high speeds and during cornering. They are firmer but not overly stiff, making them ideal for sporty driving.
• Koni STR.T: A twin-tube design that balances comfort and performance. They are slightly firmer than KYB and offer a sportier feel without sacrificing daily drivability.

Recommendation: For most owners, KYB Excel-G or Monroe OESpectrum provide the best value. For an enthusiast, Bilstein B6 is the top choice.

Coil Springs

• Moog CC-Series: Standard-height springs that restore original ride height and load-carrying ability. They are affordable and reliable.
• Eibach Pro-Kit: A mild lowering spring (about 1.0–1.2 inches drop). Lowers the center of gravity for reduced body roll while maintaining decent ride comfort. Requires quality dampers.
• H&R Sport Springs: Offer a more aggressive drop (1.3–1.5 inches) and stiffer rate. Best paired with performance shocks like Bilstein or Koni.

Note: If your car has sagging rear springs, Moog standard springs are a wise choice. Lowering springs should only be used with performance dampers to avoid poor ride quality.

Sway Bars (Anti-Roll Bars)

Upgrading the sway bars reduces body roll and improves turn-in response. The 300M benefits from a thicker front bar and a rear bar to balance understeer.

• Addco: Offers a 1-1/8″ front bar and a 7/8″ rear bar. These are solid steel and come with polyurethane bushings. A great upgrade for handling.
• Eibach: Sway bars are a bit more expensive but lightweight and highly effective. They reduce body roll without making the ride too stiff.

Installation tip: Always replace the sway bar bushings and end links when upgrading bars. Polyurethane bushings provide more precise feel than rubber.

Control Arms and Bushings

• Front lower control arms: The factory rubber bushings often crack, causing steering slop and wheel alignment changes. Use Moog or ACDelco control arms that include new ball joints and bushings.
• Rear control arms: The rear trailing arms and lateral links can be upgraded with Powerflex or Prothane polyurethane bushings. These reduce rear-end squat and improve stability.
• Strut rod bushings: Worn strut rod bushings cause a clunking noise and vague steering. Replace with Moog or Energy Suspension poly units.

Strut Mounts and Bearings

Don’t skip these. Worn strut mounts cause noise and allow the strut to shift, affecting alignment. Use Moog or Monroe replacement mounts with integrated bearings for the front. They are inexpensive and crucial for a proper rebuild.

Recommended Suspension Upgrade Combinations

Daily Driver Smooth Ride

• Struts/Shocks: KYB Excel-G (front and rear)
• Springs: Moog CC-Series (standard height)
• Sway Bars: Keep stock (or add only rear Addco bar)
• Bushings: Moog control arms, rubber mounts
• Result: Restored ride height, smooth float-free ride, and predictable handling. Minimal increase in firmness.

Sporty Handling

• Struts/Shocks: Bilstein B6 (or Koni STR.T)
• Springs: Eibach Pro-Kit (minor lowering)
• Sway Bars: Addco front and rear
• Bushings: Polyurethane for control arms and sway bar
• Result: Flatter cornering, sharper steering, and a controlled but firm ride. Suitable for spirited driving.

Budget-Friendly Refresh

• Struts/Shocks: Monroe OESpectrum
• Springs: Moog CC-Series (only replace if sagging)
• Sway Bars: Keep stock, replace end links and bushings
• Bushings: Replace only obviously worn rubber with Moog parts
• Result: Cost-effective restoration of original ride quality and safety.

Installation Considerations

Alignment After Upgrade

After replacing any suspension component—especially struts, springs, or control arms—a four-wheel alignment is mandatory. Camber and toe settings will be affected, and an improper alignment wears tires quickly and hurts handling.

Tools and Time Required

• Basic tools: Jack stands, spring compressor, wrenches, sockets, torque wrench.
• Difficulty: Moderate. Replacing struts and springs requires compressing coil springs, which is dangerous without proper tools. If you’re not experienced, have a professional install the parts.
• Time: Expect 4–6 hours for a complete front strut and rear shock replacement. Adding sway bars and control arms can double that time.

Final Recommendation

For a 1999 Chrysler 300M needing suspension work, start with the basics: replace all four struts and shocks with a quality brand like KYB or Monroe. These provide the most improvement for the cost. If the springs have sagged, add Moog standard-height springs. For those seeking better handling without excessive stiffness, pairing Bilstein B6 shocks with Eibach Pro-Kit springs and upgraded sway bars will transform the car. Always replace strut mounts, bump stops, and bellows when doing the job. A fresh suspension with aligned wheels will make your 300M feel like new again—or better.