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White Porsche 928 S4, front-right three-quarter view, photographed in Sault Ste. Marie, Ontario. Model illustration; US specification is not established. Photo: 1988 Porsche 928 S4 in Grand Prix White, Front Right, 07-27-2023.jpg by Elise240SX / Wikimedia Commons; CC BY-SA 4.0. Original photograph used unchanged.
The Porsche 928 S4 invites attention to its V8, distinctive headlights and broad rear hatch. A more revealing purchase conversation starts underneath: what condition is the rear suspension in, and what evidence shows that its geometry has been checked correctly?
The reason is the Weissach axle. Its stabilizing behavior is part of the 928's original engineering, so a specialist's suspension assessment belongs alongside the engine inspection and service history.
Establish which 928 you are inspecting
Porsche Classic's model guide identifies the S4 with model years 1987–1991 and a 5.0-liter engine. Its rounded nose, wide flush-fitting rear lights and raised black rear spoiler distinguish the factory design from earlier 928 versions.
Use those details to organize photographs before traveling. Then have the specialist reconcile the vehicle identification, original specification and installed components. A badge or familiar silhouette cannot establish what repairs and modifications occurred during decades of ownership.
Understand the movement Porsche intended
In its May 29, 2018 engineering retrospective, Porsche explains how carefully selected rubber-bushing compliance and suspension geometry help the outside rear wheel move toward toe-in when the driver releases the accelerator in a corner. The objective was more stable, manageable handling.
That is a passive mechanical response. The same article separately discusses the electronically controlled rear-axle steering used in later Porsches. Describing the S4 simply as having rear-wheel steering can therefore leave a buyer with an incomplete picture of what actually moves and why.
Porsche also describes the transaxle layout: the engine sits at the front, while the transmission is at the rear, connected through a shaft inside a rigid tube. The car's layout and its rear suspension should be understood together.
Ask for evidence from below the car
Our inspection recommendation follows from that design. Ask a technician familiar with the 928 to assess the rear suspension's bushings, joints, mounting points and evidence of previous work. Have them identify replacements and explain whether the installed parts preserve the intended behavior.
Request any alignment printout and the invoice that goes with it. An isolated sheet of numbers says less than a record identifying the car, date, mileage, workshop and work performed before measurement. Ask which factory specifications and preparation procedure the shop used.
Photograph the tires' size markings and record their condition. Have the inspector consider tire wear alongside suspension findings, rather than treating either as a diagnosis on its own. If the car has different wheels, lowered suspension or aftermarket components, make those changes explicit in the assessment.
Keep the road test ordinary
After the preliminary safety inspection, evaluate straight-ahead tracking, steering consistency and the car's response to normal road surfaces at legal speeds. Describe any movement or noise precisely, including when it occurs. Leave deliberate limit-handling or abrupt lift-off demonstrations out of a purchase appointment.
The practical question is whether this particular S4 behaves coherently and has a credible explanation for its condition. A specialist should determine whether an observation calls for adjustment, replacement or further investigation before you agree on the next step.
Build a written purchase baseline
Porsche's Classic parts catalog separates the 1987–1991 928 from earlier cars and the later GTS. Ask the workshop to identify applicable parts and confirm current availability when preparing an itemized US-dollar estimate; a catalog entry alone does not establish stock or delivery timing.
For another classic Porsche perspective, read our 930 Turbo specification guide. The S4 offers its own engineering story. Start your search with Big Boy Exotics with the suspension findings, service evidence and intended driving use clearly defined.