Quick Facts

The following table separates the enduring Series 355 specifications from details that changed during the five-year production run. Individual body dimensions, equipment, and output must still be checked against the correct annual catalogue and build record.

The model name alone does not identify the precise car. A 1931 355-A and a 1935 355-E share displacement and basic engine architecture, but they differ substantially in chassis design, styling, output, body construction details, and road behavior.

Why the Fleetwood Convertible Sedan Matters

The Convertible Sedan answered a specific prewar requirement. It gave an owner the visibility and ceremony of an open Cadillac without surrendering four-door access, wind-up glass, or a more substantial folding roof. That made it better suited to formal use and long-distance travel than a phaeton, while still offering a completely open passenger compartment when the weather allowed.

Its five-year run also records Cadillac's response to a rapidly contracting luxury market. The Series 355 began as a carefully developed descendant of the Series 353, then acquired more streamlined bodywork, greater engine output, and, in 1934, a new chassis with independent front suspension. The costly Fleetwood body remained available even as Depression-era demand forced every American luxury manufacturer to rationalize production.

For restorers, the car matters because its identity depends on the relationship between chassis, engine, Fleetwood body, hardware, and documentary evidence. A correct open body is far more than a sedan shell with its roof removed. The sill structure, door geometry, windshield, top mechanism, rear body framing, side glass, interior fittings, and weather equipment are specific to the body type.

Historical Context and Development

Cadillac after the Series 353

The 355-A replaced the closely related Series 353 for 1931. Cadillac retained the 353-cubic-inch V-8 rather than pursuing a wholly new powerplant, concentrating instead on refinement, body design, and chassis development. Above it sat Cadillac's V-12 and V-16 lines, which supplied greater cylinder count and prestige at considerably higher cost.

The Series 355 competed with Packard's Eight and Super Eight models, Lincoln's Model K, Chrysler's Imperial, and other expensive American cars built during a severe collapse in new-car demand. Cadillac could draw on General Motors engineering and production resources, while Fleetwood supplied the formal and semi-custom bodywork expected by buyers in this price class.

Fleetwood had become part of the Fisher Body organization before being absorbed into General Motors, and its name denoted Cadillac's more elaborate coachwork rather than an independent aftermarket conversion. Even so, surviving bodies retain many coachbuilding practices, including extensive structural wood, individually fitted doors, complex interior joinery, and hardware that is difficult to reproduce accurately.

From Upright Formality to Streamlining

The 1931 355-A retained a tall radiator shell, separate headlamps, pronounced running boards, and the vertical visual language of the late 1920s. The 355-B and 355-C progressively lowered and integrated the body, with revised fenders, grille treatment, hood ventilation, and glazing details. These changes are essential identification clues because restorations have often accumulated lamps, horns, wheels, and trim from adjacent years.

The 1934 355-D was the decisive break. Cadillac introduced a lower, more streamlined body and a new chassis range, including Series 10, Series 20, and Series 30 groupings on different wheelbases. Fisher supplied Series 10 bodies, while Fleetwood bodywork was associated with the longer Series 20 and Series 30 chassis. The 355-E continued the basic 1934 engineering theme for 1935 with detail revisions and increased advertised output.

No Homologation or Factory Racing Purpose

The Series 355 was not developed as a homologation model, and Cadillac did not build the Fleetwood Convertible Sedan around a factory competition program. Its engineering priorities were quietness, flexibility, braking security, steering stability, and body isolation. Any competition appearance by an individual car should be documented as that car's later history, not presented as a factory motorsport specification.

Engine and Drivetrain

Cadillac's 353-cubic-inch V-8 used a 90-degree cylinder arrangement and side valves in the block. Its bore and stroke were approximately 3.375 by 4.9375 inches, producing a long-stroke engine intended to deliver useful torque at modest crankshaft speed rather than high-rpm power. Detachable cylinder heads made decarbonizing and valve work more practical than on earlier fixed-head designs.

Fuel was supplied by carburetion, with intake, carburetor, and air-cleaner details changing over the production run. Distributor-and-coil ignition fired eight spark plugs, while a conventional liquid-cooling system used a belt-driven fan and radiator. Pressure lubrication served the engine's principal bearings, but any rebuild must follow the oiling arrangements and clearances specified for the particular year rather than later overhead-valve Cadillac practice.

A dry single-plate clutch connected the V-8 to a three-speed manual gearbox. Cadillac's synchromesh development made the transmission more manageable than many earlier crash gearboxes, although first gear remained primarily useful for starting the heavy car. A propeller shaft carried power to a conventional rear axle.

The table records specifications that can be applied across the family or tied to a documented model year. Compression ratios, carburetor models, axle ratios, and torque figures are not included because references differ by year, body, and equipment.

The numerical output increase does not tell the entire story. Changes to induction, exhaust flow, compression, and calibration improved the later engine's ability to move increasingly streamlined cars, but the fundamental driving technique remained the same: use the V-8's low-speed pull, make deliberate shifts, and avoid treating the long-stroke unit like a modern high-speed engine.

Chassis, Suspension, Steering, and Brakes

All Series 355 models used separate body-and-frame construction. On a Fleetwood Convertible Sedan, the frame carried not only the drivetrain and suspension loads but also a long, four-door open body with no fixed steel roof to help maintain alignment. Sound structural wood, intact mounting points, correct body shims, and a frame free of twist are therefore central to the way the doors, windshield, and top fit.

The 1931 through 1933 cars retained a conventional front axle suspended by leaf springs. For the 355-D in 1934, Cadillac adopted independent front suspension of the enclosed knee-action type, a major change in both ride quality and steering behavior. The rear remained a live axle located by semi-elliptic leaf springs.

Steering was by a mechanical steering box without power assistance. Large steering wheels supplied leverage at parking speed, while the long wheelbase and conservative alignment produced deliberate rather than quick response. Four-wheel mechanical brakes were used during the Series 355 era, with control and assist arrangements varying by year and specification, so restorers must identify the correct linkage before ordering parts.

This chassis table is most useful when separating the earlier 355-A through 355-C cars from the redesigned 355-D and 355-E.

The 1934 redesign should never be reduced to a styling update. Independent front suspension allowed each front wheel to react to road irregularities with less disturbance at the opposite side, while the lower chassis helped Cadillac produce a more modern stance. The knee-action units, however, require specialist rebuilding when worn or leaking.

Driving Experience and Road Behavior

A correctly rebuilt Series 355 starts with a quiet, low-frequency V-8 beat rather than an aggressive exhaust note. Throttle response is progressive, and the engine gathers speed through torque rather than a rush at the top of the rev range. In normal driving, an experienced driver shifts early and allows third gear to carry the car once traffic and gradient permit.

The clutch should engage smoothly despite the mass of the car. Gear selection rewards an unhurried hand, particularly when the lubricant is cold, and first gear is not intended for sustained use. Excessive gear noise, jumping out of gear, or a clutch that chatters through the body points to wear or poor alignment rather than normal prewar character.

At low speed the steering is heavy, especially with side-mounted spare wheels and wide-period tires adding mass over the front axle. Once moving, the long wheelbase settles the car into a steady line. A 355-A feels more connected by axle movement and steering kickback, while a properly rebuilt 355-D or 355-E isolates broken pavement more effectively through its independent front suspension.

Body roll is substantial by modern standards, but a sound car should not wander uncontrollably or continue oscillating after a bump. Worn spring shackles, incorrect caster, deteriorated dampers, loose steering joints, unsuitable tires, and flexible body mounts can turn stately responses into instability.

Mechanical brakes demand anticipation and even adjustment at all four wheels. Pedal travel should be predictable, and the car should stop without pulling sharply to one side. Modern traffic places greater demands on both braking distance and cooling, making defensive road positioning part of driving any Series 355.

Identification and Originality

Serial, Engine, and Fleetwood Body Records

A Series 355 predates the standardized 17-character VIN. Identification begins with the correct annual series, the chassis or serial stamping, the engine number, and the Fleetwood body tag or number plate. Their locations and formats should be confirmed against Cadillac documentation for the applicable year because restorations, replacement engines, and local registration practices have altered many surviving records.

The 355-A, 355-B, 355-C, 355-D, and 355-E suffixes are not decorative trim grades. They identify successive model years and, in the case of the 355-D redesign, substantially different chassis engineering. A title that merely says “355” is insufficient evidence that every major component belongs to the same year.

Fleetwood body numbers are especially important for a Convertible Sedan. The body tag should correspond to an open four-door style, but no unsupported body-number decoding should be accepted from a seller without a factory body catalogue, build sheet, or recognized marque reference. Body plates can be transferred, and a genuine plate does not by itself prove that the body beneath it is original.

What Matching Numbers Means on a Prewar Cadillac

“Matching numbers” is often used too loosely in the prewar market. The defensible claim is that the engine, chassis, and body identifiers agree with factory records or accepted production sequences and that the major assemblies are correct for the build. Cadillac documentation, historical registrations, early photographs, ownership records, restoration invoices, and correspondence with marque specialists carry more weight than a recently prepared display board.

Date-coded electrical components, carburetor castings, generator and starter tags, wheel details, instruments, and hardware can support a car's chronology. They should not be treated like the rigid date-code system used to judge some postwar muscle cars, however. Service replacement parts were normal over a long working life, and evidence must be interpreted in context.

Coachwork Details That Expose an Incorrect Car

A real Convertible Sedan requires the correct windshield frame, cowl structure, door tops, side-window regulators and channels, top irons, rear tub, roof well, belt molding, and interior garnish pieces. Converting a closed sedan removes structural and geometric features without supplying the factory open-car reinforcements. Door sag, an improvised windshield, generic top bows, or rear doors that conflict with the roof mechanism should prompt a detailed inspection.

Common substitutions include later sealed-beam headlamp conversions, incorrect horns, modern gauges, alternators disguised as generators, replacement carburetors, generic ignition components, unsuitable hydraulic brake conversions, and wheels from neighboring Cadillac or LaSalle series. Some modifications improve usability, but they must be disclosed and should not be represented as factory equipment.

Paint and upholstery should be judged against annual Cadillac and Fleetwood material references, not assumptions about what looks suitably formal. Surviving examples often acquired two-tone schemes, contrasting moldings, vinyl interiors, modern carpet, and bright chrome where nickel, painted, plated, or wood-grained finishes originally differed. A factory build record is the strongest starting point for color, trim, and optional equipment research.

Annual Variant and Chassis Breakdown

Cadillac treated each model year as a distinct development of the Series 355. The table summarizes the accepted annual designations and advertised horsepower, while avoiding unsupported production totals for the Fleetwood Convertible Sedan.

Exact Convertible Sedan production numbers are not consistently documented in general references and should not be inferred from total Series 355 production. Fleetwood bodies were catalogued in small quantities, and totals sometimes cited for an individual style require confirmation from annual body records.

Performance and Dimensional Specifications

Cadillac published engine output and chassis dimensions, but comparable instrumented acceleration tests are scarce for coachbuilt luxury cars of this period. Body weight, axle ratio, road surface, fuel, weather, and test method could materially alter any maximum-speed result.

No single curb weight or top-speed figure fairly represents every Fleetwood Convertible Sedan from 1931 through 1935. Coachwork, side-mount equipment, luggage fittings, wheelbase, and annual construction changes affected mass, while period maximum-speed figures are not sufficiently consistent to present as one definitive specification. Standardized 0–60 mph and quarter-mile data are likewise not broadly documented for this body style.

Compared With Related Cadillac Models

Series 353

The Series 353 was the immediate predecessor and shared the 353-cubic-inch V-8 displacement that gave the later 355 its numerical identity. A 1930 Series 353 should not be reclassified as a 355 merely because the engine is closely related. Radiator treatment, body catalogues, chassis numbering, and year-specific components establish the distinction.

Cadillac V-12 and V-16

Cadillac's V-12 and V-16 cars offered smoother power delivery, greater cylinder count, longer chassis possibilities, and some of Fleetwood's most elaborate custom bodies. They also impose higher restoration costs through additional cylinders, more complex engine components, and scarcer model-specific parts. The Series 355 V-8 is mechanically less daunting, but an open Fleetwood body's wood and hardware can still make its restoration as demanding as that of a more expensive closed multi-cylinder Cadillac.

LaSalle

LaSalle shared General Motors resources and Cadillac sales connections but was a separate marque with its own series identity, styling, dimensions, and mechanical specifications. Lamps, wheels, instruments, and hardware may appear similar enough to invite substitutions. Similar appearance is not evidence of interchangeability or factory correctness.

Series 10, 20, and 30

For 1934 and 1935, the 355-D and 355-E encompassed different chassis lengths and body sources. The Series 10 used the shorter 128-inch chassis and Fisher bodies, while Fleetwood coachwork appeared on the longer Series 20 and Series 30 platforms with 136- and 146-inch wheelbases. A buyer should identify the body and chassis combination rather than assuming every 1934 or 1935 Series 355 shares the same frame.

Ownership and Restoration Notes

Engine and Cooling System

The long-stroke V-8 is durable when assembled with correct bearing clearances, oil pressure, cooling capacity, and ignition timing. Years of storage can leave sludge in the crankcase and oil passages, while corrosion and scale reduce radiator and block flow. A car that runs quietly for several minutes in a showroom may still overheat under road load.

Rebuilding requires a machine shop familiar with prewar side-valve engines. Cylinder-head flatness, block cracks, valve seats and guides, main and connecting-rod bearings, oil-pump condition, water distribution, and flywheel balance all deserve attention. Installing modern bearing materials or seals without understanding the original oiling system can create new problems.

Transmission, Clutch, and Rear Axle

Gear wear, tired bearings, damaged synchronizer components, clutch contamination, and hardened seals are normal concerns after decades of intermittent use. A worn driveline can transmit vibration through the long body and accelerate damage to mounts and joints. Correct lubricant matters because some modern extreme-pressure oils are unsuitable for vintage yellow-metal components.

Wood Framing and Open-Body Structure

The body is usually the largest financial risk. Ash framing can decay beneath apparently acceptable paint and upholstery, particularly around the sills, door pillars, cowl, roof well, and rear body mounts. Once the wood moves, doors sag, latches cease to align, glass channels bind, and the top no longer meets the windshield correctly.

A proper wood restoration requires patterns, coachbuilding skill, and repeated trial fitting on a dimensionally correct frame. Replacing isolated pieces without bracing and measuring the body may lock in distortion. The doors, windshield, top irons, hood, and body mounts should be fitted before final paint and upholstery.

Parts Availability

Routine ignition, bearing, gasket, brake-lining, and electrical work can be supported by specialist suppliers, established rebuilders, and Cadillac clubs. Fleetwood-specific castings, latches, window regulators, garnish moldings, top hardware, instruments, and decorative trim are much harder to source. Reproduction items exist for selected applications, but fit, plating, typography, and dimensions should be compared with original pieces.

A complete but worn car is usually a safer restoration basis than a cosmetically attractive project missing its top mechanism or body hardware. Fabricating one absent bracket may be manageable. Reconstructing an entire roof system from photographs can consume hundreds of specialist hours.

Buyer and Inspection Points

A serious inspection should take place with the car on a lift, the top operated, all four doors opened and closed, and the engine brought fully to operating temperature. The following checks address the failures most likely to change the financial outcome of a purchase.

Inspection priorities should follow cost and scarcity, not visual impact. Tired paint can be evaluated and renewed by many competent shops. A missing Fleetwood windshield casting, distorted top assembly, or incorrectly rebuilt body frame can stop a restoration for years.

Collector and Market Relevance

Open Fleetwood coachwork generally attracts more collector attention than the more numerous closed sedans because it combines formal Cadillac design with fully open motoring. The four-door Convertible Sedan is also substantially more complicated than a roadster or convertible coupe, giving originality and completeness unusual weight in any valuation.

Collectors typically reward a documented factory body, correct annual-series components, an intact top mechanism, sound structural wood, proper instruments and hardware, and restoration work supported by photographs. Awards and concours presentation can strengthen provenance, but they do not replace verification of numbers, body construction, and historical records.

Series 355 Cadillacs are recognized within the Classic Car Club of America's Full Classic field, giving them an established place in tours, judging, and preservation culture. The Cadillac & LaSalle Club and specialist prewar communities provide technical knowledge, historical literature, and access to owners who understand the differences among 355-A through 355-E cars.

Market behavior varies sharply according to body style. A closed sedan may provide a less costly route into Series 355 ownership, but its value cannot be used mechanically to appraise an authentic Fleetwood Convertible Sedan. Conversely, an open-looking conversion should not be priced as factory Fleetwood coachwork without persuasive physical and documentary evidence.

Cultural and Design Relevance

The Convertible Sedan belongs to the period when an open luxury car could serve both private owners and formal transportation. Its four doors, upright rear compartment, substantial beltline, and folding roof retained the visual authority of a chauffeur-driven town car while allowing the entire cabin to open to the air.

The design's transition across five years is equally instructive. Early cars wear tall grilles, separate lamps, exposed running boards, and clearly articulated fenders. By 1934, the radiator and body sat lower, the fenders flowed more decisively around the wheels, and the windshield and passenger compartment appeared more integrated with the chassis.

The Series 355 has no meaningful factory racing legacy, and attempts to manufacture one obscure its actual contribution. Its history lies in American coachbuilding, long-distance touring, club preservation, concours restoration, and the engineering transition from rigid front axles to independent suspension. Surviving cars are often seen on Classic Car Club tours and formal concours fields rather than competition grids.

Frequently Asked Questions

What engine is in the 1931–1935 Cadillac Series 355?

The Series 355 used Cadillac's naturally aspirated 353-cubic-inch, approximately 5.8-liter, L-head V-8 throughout the five-year run. Advertised output rose from 95 hp in the 1931 355-A to 130 hp in the 1935 355-E.

What is the difference between the 355-A, 355-B, 355-C, 355-D, and 355-E?

Each suffix identifies an annual series: 355-A for 1931, 355-B for 1932, 355-C for 1933, 355-D for 1934, and 355-E for 1935. Styling, output, equipment, and chassis details changed, with the 355-D introducing the new multi-wheelbase chassis range and independent knee-action front suspension.

How can a genuine Fleetwood Convertible Sedan be identified?

Identification requires agreement among the chassis or serial data, engine number, Fleetwood body tag, physical body construction, and period documentation. Correct four-door open-body framing, roll-up window mechanisms, windshield structure, top irons, roof well, and body hardware are as important as the tag itself.

Does a Series 355 have a modern VIN?

No. It predates the standardized 17-character VIN. Buyers must use year-specific Cadillac serial and engine records, Fleetwood body information, title documents, and factory or club references rather than applying a modern VIN-decoding method.

What are the most expensive Series 355 Convertible Sedan restoration problems?

Rotten structural wood, a damaged or twisted frame, missing Fleetwood top hardware, absent window mechanisms, and incomplete body trim usually present the greatest financial risk. A full engine rebuild and worn 1934–1935 knee-action suspension can also be costly, but incomplete coachwork may be harder to solve because patterns and replacement pieces are scarce.

Are mechanical parts available for the Cadillac Series 355?

Many service items can be rebuilt or sourced through prewar Cadillac specialists, clubs, and established suppliers. Fleetwood body hardware, top components, instruments, decorative castings, and year-specific trim are much less available, making completeness a major purchase criterion.

Why is the Fleetwood Convertible Sedan collectible?

It combines Cadillac's 353-cubic-inch V-8 chassis with a costly, low-survival four-door open body built by Fleetwood. Collectors also value the model's annual 355-A through 355-E development, its eligibility as a Full Classic, and the substantial difference between authentic coachwork and later conversions.

Collector Takeaway

The Series 355 Fleetwood Convertible Sedan deserves scrutiny at the level of an individual coachbuilt object, not merely as an old Cadillac with an attractive folding roof. The correct car preserves a linked set of evidence: annual-series chassis, 353-cubic-inch V-8, Fleetwood body identity, open-car structure, window and top mechanisms, and documentation that explains how those pieces came together.

Its strongest historical argument is visible underneath the body. A 1931 355-A records the mature beam-axle Cadillac of the early Depression years, while a 1934 355-D or 1935 355-E adds independent front suspension and the lower proportions of Cadillac's next design phase. Find one with an honest body, complete hardware, and a documented restoration, and the result is not simply formal transportation. It is a working record of how Cadillac and Fleetwood carried traditional coachbuilding into a new chassis era.