Porsche 997 Rear Top Mount Isolator Bushings
Porsche Suspension Bushings by PowerFlex
Let’s face it, suspension bushings on a Porsche can endure high stress, lateral loads, torsional twist, and thermal cycling, often in harsh conditions with very little maintenance or lubrication. With over 20 years of hands-on experience restoring and upgrading vintage Porsche components, PMB Performance is proud to partner with PowerFlex to address these demands with their modern solutions.
Porsche 997 Rear Top Mount Isolator Bushings
The Porsche 911 (997), produced from 2005 to 2012, relies on the Rear Top Mount Isolator Bushings to anchor the top of its rear shock absorbers to the chassis, a key element in its sophisticated suspension system. These bushings, typically made of rubber or upgraded polyurethane, isolate vibrations, reduce noise, and ensure smooth load transfer between the shocks and the car’s body, enhancing both comfort and handling precision. In the 997’s rear-engine layout, they contribute to the model’s renowned balance and responsiveness. Over time—often after 60,000-80,000 miles—wear from spirited driving or age can degrade these bushings, leading to clunking, harshness, or a less planted feel. Replacing them with high-quality isolator bushings restores the refined ride and sharp dynamics, keeping the 997’s performance true to its Porsche heritage, whether on the street or track.
The Problem with OEM Bushings
Porsche OEM bushings use a rubber compound—typically 60-70 Shore A hardness—that degrades over time. Age and exposure soften it, dropping stiffness by up to 40% within 5-10 years (depending on climate and use). Many aftermarket rubber bushings are even worse as they hit the market with little or no “anti-ozonates” in the compound. This increases compliance, allowing unwanted suspension movement. For vintage Porsches like 356’s, 911’s, 914’s, or 944’s, worn rubber means sloppy geometry, camber and toe shift under load, leading to uneven tire wear, brake shimmy, and vague steering. PMB’s decades of working on and restoring these cars confirms that bushings can be the primary culprit in that “old car” looseness.
The PowerFlex Solution
PowerFlex bushings tackle this with a proprietary polyurethane compound, formulated at 80-85 Shore A hardness—25-30% stiffer than fresh OEM rubber. Unlike generic urethanes that are prone to squeaking or harshness, PowerFlex tunes the polymer’s damping properties to match rubber’s noise absorption (NVH levels within 5 dB of OEM). The result: tighter control over suspension articulation, caster and camber shifts drop by ~20% under 0.8g cornering loads without sacrificing ride quality.
Even new Porsches can gain from PowerFlex’s design. Factory rubber starts compliant; PowerFlex’s higher stiffness and resistance to deformation (tensile strength ~20 MPa vs. rubber’s ~10 MPa) sharpen response from day one. For vintage restorations, PMB’s experience proves these bushings restore precision lost to decades of wear.
Material & Design Specs
- Polyurethane: 80-85 Shore A, cured to a Tg above 200°F for heat stability.
- Stiffness Gain: 25-30% over new rubber, verified via static load testing.
- Fitment: Modeled from OEM Porsche bushings, tolerances ±0.1mm, no mods needed.
- Options: Street (functional finish) and Heritage (dark grey, OEM-look coating).
Why PowerFlex with PMB?
- Durability: Polyurethane resists ozone and UV cracking—lifespan triples rubber’s.
- Control: Reduces suspension play, cuts tire wear, stabilizes braking.
- Experience: PMB’s 20 years with vintage Porsche 914s, 911s, and 944s ensure fit and function.