Complete Guide to 99 Grand Prix Rear Suspension Parts

The rear suspension of a 1999 Pontiac Grand Prix is a multi-link independent setup designed for a balance of ride comfort and handling. Over time, components wear out, leading to poor ride quality, noise, and uneven tire wear. This guide covers the essential rear suspension parts for the 99 Grand Prix, what to look for when they fail, and how to choose replacements.

Rear Suspension Components Overview

The 1999 Grand Prix uses a four-link rear suspension with coil springs, separate shock absorbers (or struts on some models), and a stabilizer bar. Key parts include:

• Rear Shock Absorbers / Struts – Control vertical motion; some models have struts that serve as a structural component.
• Coil Springs – Support the vehicle’s weight and absorb road impacts.
• Control Arms – Upper and lower arms that locate the rear axle and control wheel alignment.
• Trailing Arms – Connect the rear axle to the chassis, controlling fore-aft movement.
• Stabilizer Bar (Sway Bar) – Reduces body roll during cornering.
• Bushings – Rubber or polyurethane inserts that isolate vibration and allow articulation at pivot points.
• Ball Joints (some models) – Allow pivot movement between control arms and knuckle.

Rear Shocks vs. Struts

Most 1999 Grand Prix models use separate shock absorbers mounted outside the coil springs. However, some trim levels (like the GTP) may have struts that integrate the spring and shock into a single unit. Check your vehicle’s RPO codes or VIN to confirm. Shocks are simpler to replace; struts require spring compression and careful handling.

Common Symptoms of Worn Rear Suspension Parts

• Bouncy, unstable ride, especially over bumps.
• Rear end sagging (lower ride height on one side).
• Clunking, squeaking, or rattling noises from the rear.
• Uneven tire wear on rear tires.
• Poor handling, excessive body roll in corners.
• Rear alignment issues (camber or toe out of spec).

Diagnosing the Culprit

Before buying parts, inspect the rear suspension visually. Look for:

• Leaking fluid from shock absorbers.
• Cracked or collapsed coil springs.
• Worn, cracked, or missing bushings.
• Loose or bent control arms.
• Damaged stabilizer bar links or bushings. A simple bounce test: push down on the rear bumper; if it bounces more than once, shocks are likely worn.

Replacement Parts & Considerations

When replacing rear suspension parts, you have options between OEM, aftermarket, and performance upgrades. Here’s what to consider for each major part.

Shock Absorbers / Struts

• OEM Replacement: Monroe, Gabriel, or KYB make direct-fit replacements that match stock ride quality. Expect to pay $40–$80 per shock.
• Performance Upgrades: Bilstein or Koni offer monotube shocks with better damping control, improving handling without sacrificing comfort. These cost $80–$150 each.
• Quick-Strut Assemblies: For models with struts, a pre-assembled unit (spring + strut) saves time and eliminates the need for spring compressor rental. Brands like Monroe Quick-Strut are common.

Coil Springs

• Standard Replacement: Moog or AC Delco springs restore original ride height and load capacity. Cost around $60–$100 per spring.
• Lowering Springs: If you want a sportier look and lower center of gravity, Eibach or H&R make progressive-rate springs that lower the car about 1–1.5 inches. Expect firmer ride.
• Air Springs: Some owners convert to air bags for adjustable load leveling, but this is less common on a budget.

Control Arms & Bushings

• Complete Control Arms: New arms with pre-installed ball joints and bushings are easier to install than pressing out old bushings. Moog and Dorman offer affordable options ($70–$120 per arm).
• Bushings Only: Polyurethane bushings (Energy Suspension, Prothane) reduce compliance and improve steering response, but transmit more noise and vibration. They’re more durable than rubber.

Trailing Arms & Stabilizer Bar Components

• Trailing Arms: Generally only replaced if bent or if bushings are completely shot. Aftermarket adjustable trailing arms allow for fine-tuning rear toe.
• Stabilizer Bar Links: These small links often fail and cause clunking. Replace with Moog or OEM links ($15–$30 each).
• Sway Bar Bushings: Replacing the rubber bushings where the bar mounts to the chassis is a cheap fix for excessive body roll.

Installation Tips & Costs

Replacing rear shocks or struts is a moderate DIY job if you have basic tools and a floor jack. Spring replacement requires a spring compressor – if unsure, have a professional do it for safety. Shop labor rates for a complete rear suspension overhaul can run $300–$600, depending on parts included.

• Always replace shocks/struts in pairs (both rear).
• Check and replace the rear sway bar links and bushings at the same time – they’re inexpensive and often worn.
• After replacing multiple components, get a rear alignment to ensure even tire wear and proper handling.

Tools Needed for DIY

• Jack and jack stands
• Socket set (metric)
• Torque wrench
• Spring compressor (for strut or spring replacement)
• Penetrating oil (like PB Blaster) for rusted bolts
• Pry bar for bushing removal

Recommendation: Which Parts to Buy?

For a daily-driven 1999 Grand Prix, stick with quality OEM-level replacements from Monroe, KYB, or Moog. They offer reliability without breaking the bank. If you plan to keep the car for several more years and want sharper handling, consider Bilstein shocks and Moog control arms with polyurethane bushings.

Avoid economy brands that cost half as much – they often fail quickly or degrade ride quality. If you’re on a tight budget, used OEM parts may be an option, but inspect them carefully for wear.

Final advice: Start with shocks and springs if your car bounces or sags. Then assess bushings and control arms if you hear clunks or have alignment issues. Replacing everything at once can save labor but may be overkill if some parts are still good. A thorough inspection is your best guide.

Keep your 1999 Grand Prix’s rear suspension in good shape – it makes a noticeable difference in comfort and safety on the road.