Question 1

Floor Pan Corrosion

Accepted Answer

The floor pans develop rust, perforation, and structural weakness. In severe cases, you can see the road through the floor. The driver's footwell and the area around the pedal box are particularly vulnerable. The 356 floor pan is mild steel with no galvanising. Road spray attacks from below while moisture from leaking windscreen seals, door seals, and condensation attacks from above. The floor pan sits close to the road surface, and stone chips remove any protective coating. Replacement floor pans are available from specialists like Stoddard and Restoration Design. Fitting requires stripping the interior, removing the seats and pedal assembly, cutting out the old pan, and welding in the new one. The new pan must be correctly aligned to maintain the body's geometry. Cost: $8,000-$20,000 at a specialist depending on extent and whether heater channels are also affected.

Question 2

Heater Channel Rot

Accepted Answer

The sills (rocker panels) that run along each side of the car are actually heater channels, hollow box sections that carry warm air from the engine compartment to the cabin. They corrode from the inside out, and by the time you see external rust, the structural integrity is already compromised. Warm, moist air from the engine-driven heater system condenses inside the channels. Drain holes block with debris. The channels rot from inside, hidden from view by external trim and undercoating. Replacement heater channels are available as reproduction parts. Fitting is major surgery, the car essentially needs to be separated at the sills, the old channels cut out, and new ones welded in with precise alignment. This is the most significant body repair on a 356. Cost: $10,000-$25,000 per side at a specialist body shop.

Question 3

Battery Box Corrosion

Accepted Answer

The metal surrounding the battery in the front compartment corrodes through from acid exposure. The corrosion spreads to adjacent panels and structural members. Lead-acid batteries vent acid vapour during charging, and minor spills during topping-up eat through mild steel. The battery box area is enclosed, trapping acid fumes. Remove the battery, neutralise the acid with baking soda solution, and assess the damage. Surface corrosion can be treated with rust converter and sealed. Perforated metal requires cutting out and welding in repair patches. Some owners fit a fibreglass battery box liner to protect the metal. Cost: $500-$3,000 depending on severity.

Question 4

Longitudinal Member (Helly) Corrosion

Accepted Answer

The main longitudinal structural members that run beneath the floor develop rust and lose structural integrity. These members carry the suspension loads and are critical to the car's structure. Road spray, trapped moisture, and general age. Original undercoating traps moisture against the metal when it develops cracks, the undercoating that was meant to protect actually accelerates corrosion. Specialist fabrication and welding. This is not a bolt-on repair, the members must be carefully reinforced or replaced with correctly profiled steel. Cost: $5,000-$15,000 depending on severity. A car with both longitudinals gone is approaching the threshold where restoration becomes uneconomic.

Question 5

Oil Leaks

Accepted Answer

Oil weeping or dripping from the pushrod tube seals, rocker cover gaskets, case halves, main seal, and oil cooler connections. A warm 356 engine will have oil residue on virtually every surface. The 356 engine uses simple gaskets and seals that were never designed for zero-leak performance. The case halves are sealed with a paper gasket and secured with through-bolts, as the case bolts lose torque over decades, the joint weeps. Pushrod tube seals are spring-loaded rubber seals that harden with heat cycling. A complete reseal addresses all leak points in one session. Pushrod tube seals: $200-$400 for parts plus labour. Case half reseal requires engine removal and splitting the case, this is effectively a partial rebuild. Cost for full reseal: $2,000-$4,000 at a specialist.

Question 6

Cylinder Wear and Low Compression

Accepted Answer

Reduced power, increased oil consumption, blue smoke under acceleration, and difficulty starting. Compression readings below 100 psi or uneven across cylinders. The 356's air-cooled cylinders and pistons wear over time, particularly if the engine has been run without adequate warm-up, with dirty oil, or with the wrong oil viscosity. The cooling system (such as it is, an engine-driven fan and air ducting) must be intact for even cylinder temperatures. Blocked or damaged cooling tinware causes localised overheating and accelerated wear. Cylinder and piston replacement (available in standard and oversize). A top-end rebuild includes new cylinders, pistons, rings, valve job, and new pushrod tube seals. Cost: $3,000-$6,000 for parts and labour. If the crankcase is worn (main bearing surfaces), a full engine rebuild is $8,000-$15,000.

Question 7

Generator and Charging Issues

Accepted Answer

The red generator light stays on, the battery goes flat, headlights dim at idle. The 6-volt system (Pre-A through B T5) is particularly marginal. The 356 uses a generator (not an alternator) that produces limited output, especially at idle. The generator brushes wear, the commutator develops grooves, and the voltage regulator fails. On 6-volt cars, the already-limited output makes every component work harder. Generator rebuild: $300-$600. Voltage regulator replacement: $100-$200. Many owners convert to an internally regulated alternator that fits in the generator housing, this provides significantly more charging capacity. Cost for alternator conversion: $400-$800.

Question 8

Carburettor Issues

Accepted Answer

Rough idle, flat spots during acceleration, poor fuel economy, difficulty starting. Black smoke from the exhaust (rich running) or backfiring through the carburettor (lean running). The Zenith and Solex carburettors used on standard 356 engines are simple but sensitive to wear. Throttle shaft bushings wear and develop air leaks. Float valves stick or leak. Accelerator pump diaphragms perish. Idle jets block with debris or varnish from old fuel. A thorough carburettor rebuild addresses most issues. Rebuild kits are available from $40-$80 per carburettor. Worn throttle shaft bushings require re-bushing by a specialist. Replacement carburettors (new old stock or remanufactured) are $400-$800 each. A pair of rebuilt Zeniths or Solexes with new bushings: $1,000-$1,500.

Question 9

Second Gear Synchro Wear

Accepted Answer

Second gear crunches or grinds on downshifts, particularly when cold. Eventually it grinds on upshifts as well. Second gear synchro takes the most abuse in normal driving, every downshift from third loads the synchro. The brass synchro ring wears over decades of use until it can no longer equalise shaft speeds before engagement. Gearbox rebuild with new synchro rings. The transaxle must be removed from the car. Cost: $3,000-$6,000 at a specialist.

Question 10

Ring and Pinion Noise

Accepted Answer

A pronounced whine or howl from the rear of the car that changes with speed and load. The noise may be louder on the overrun (deceleration) or under power. The ring and pinion gears in the transaxle wear or were incorrectly set up during a previous rebuild. Bearing preload affects mesh pattern, worn bearings allow the gears to shift position and develop noise. Ring and pinion replacement and correct setup by an experienced specialist. This is precision work, the mesh pattern must be correct for quiet operation and long life. Cost: $2,000-$5,000 including parts and labour.

Question 11

Front Torsion Bar Sag

Accepted Answer

The front of the car sits lower than factory specification. The ride becomes harsh and bottoms out over bumps. Front tyre wear increases. The laminated torsion bar leaves fatigue over decades, losing their spring rate. Heat, corrosion between the leaves, and accumulated loading cycles all contribute. Replace the torsion bar leaves. The front suspension must be partially disassembled to access the torsion bars. Cost: $500-$1,500 for parts and labour.

Question 12

King Pin Wear (Pre-A and A)

Accepted Answer

Steering shimmy at speed, wandering on straight roads, uneven front tyre wear. Clunking from the front suspension over bumps. The front suspension uses king pins (vertical pivots that allow the front wheels to steer). The king pin bushings wear with mileage and age, developing play that allows the wheel to move in directions it should not. King pin bushing replacement. The front suspension must be partially disassembled, the king pins removed, and new bushings pressed in and reamed to size. Cost: $400-$800 per side.

Question 13

Rear Axle Boot Failure (Swing Axle)

Accepted Answer

Grease leaks from the rear axle boots. If the boots have been leaking for some time, the CV joints (actually, the swing axle pivot bearings) run dry and develop play and noise. The rubber boots that seal the rear axle pivot points crack and tear with age and heat exposure. Replace the boots and regrease the pivots. If the bearings are damaged, the axle assembly must be rebuilt. Boot replacement: $200-$400 per side. Axle rebuild: $600-$1,200 per side.

Question 14

Wiring Insulation Degradation

Accepted Answer

Intermittent electrical faults, blown fuses, dead circuits, and, in the worst case, electrical fires. The cloth or rubber insulation on the original wiring harness becomes brittle and cracks, exposing bare copper conductors. 60+ years of heat cycling, particularly in the engine bay where temperatures are high. The original insulation materials were not designed for this longevity. A complete rewiring harness is the proper solution. YnZ's Yesterdays Parts and other specialists produce exact reproduction harnesses. Cost: $1,500-$3,000 for the harness plus $2,000-$4,000 for installation. Partial repairs (replacing individual damaged wires) are a temporary fix.

Question 15

6-Volt System Limitations

Accepted Answer

Dim headlights, slow starter cranking (especially in cold weather), difficulty running modern accessories (radio, USB charger). The 6-volt electrical system used on Pre-A through B T5 models has limited current capacity. Every component draws proportionally more current at 6 volts compared to 12 volts, and the generator's output is marginal. A 12-volt conversion involves replacing the generator (or converting to an alternator), voltage regulator, all bulbs, ignition coil, and wiper motor. The starter motor may also need replacement or conversion. Cost: $800-$2,000 for a complete conversion. Alternatively, live with the 6-volt system and keep the battery in good condition.

356

356 known problems