Porsche 928 Rear Sway Bar Bushing 21mm
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 928 Rear Sway Bar Bushing 21mm
The Porsche 928, produced from 1978 to 1995, utilizes the Rear Sway Bar Bushing - 21 mm as an essential component in its rear suspension system. Designed specifically for a 21 mm rear sway bar, this bushing—typically made of rubber or upgraded polyurethane—secures the sway bar to the chassis, reducing body roll and enhancing handling stability during cornering. It also helps dampen vibrations and noise, contributing to the 928’s refined grand-touring character. Over time, wear from driving or age can degrade the bushing, leading to looseness, clunking, or reduced responsiveness, particularly noticeable in earlier models with this size bar. Replacing it with a high-quality 21 mm bushing is a key maintenance step for 928 owners aiming to maintain the car’s balanced, precise dynamics on the road. Note that some early 928s (1978-1979) used this 21 mm size, while later models often upgraded to a 22 mm bar, so verifying the sway bar diameter is recommended before replacement.
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.