Datsun 240Z / 260Z / 280Z, Known Issues and Common Problems
Overview
The Datsun 240Z (1969-1973), 260Z (1974-1976), and 280Z (1977-1978) are mechanically straightforward sports cars built around the L-series inline-six engine, an iron-block, overhead-cam design that is fundamentally tough and long-lived. The L24, L26, and L28 engines were designed for durability over outright performance, and with basic maintenance they can cover enormous distances.
However, these cars are now 48-57 years old. Every failure on this list is a function of age, and every Z-car on the road will exhibit at least several of these issues. The good news is that the Z-car community has decades of experience addressing every problem, parts are available from specialists worldwide, and the mechanical simplicity of the L-series engine makes most repairs accessible to a competent home mechanic.
Rust
Structural Rust, Floors, Sills, Strut Towers
What happens: Perforations in the floor pans, sill (rocker panel) box sections, and front strut tower mounting points. In advanced cases, the floorboard flexes underfoot, the sills crumble when prodded, and the strut towers crack under suspension load.
Why it happens: The Z-car was not well-protected from the factory. Minimal rustproofing, combined with seam-sealed joints that trap moisture, means water gets in and cannot get out. Australian coastal cars are worst affected, but any Z-car that has not been proactively rustproofed will have some degree of structural corrosion.
How to fix it: Depends on severity. Surface rust can be treated with rust converter and encapsulated. Perforated floors require panel replacement, either reproduction floor pans (available from US suppliers like Tabco and Motor Sport Auto) or custom fabrication. Sill replacement requires cutting out the old box sections and welding in new steel, a job for an experienced panel beater. Strut tower repair is critical and must be done properly, poor repairs compromise handling and safety. Budget $5,000-20,000+ for comprehensive structural rust repair, depending on severity.
Severity: Critical. Structural rust makes the car unsafe and destroys its value.
Battery Tray Corrosion
What happens: The battery tray (right-hand side of engine bay on RHD cars) corrodes and eventually perforates. Rust spreads into the inner guard and firewall.
Why it happens: Battery acid vapour attacks the steel. Older cars with non-sealed batteries are particularly vulnerable. Even sealed batteries produce enough vapour to cause damage over decades.
How to fix it: Replace the battery tray. Reproduction trays are available ($100-250). If rust has spread into the inner guard, the surrounding metal must be cut out and replaced. Prevent recurrence by coating the new tray with POR-15 or similar rust encapsulator and fitting a sealed battery.
Severity: Needs attention. Localised but can spread into structural areas if ignored.
Spare Wheel Well Rust
What happens: The floor of the boot around and beneath the spare wheel well rusts through. Water pooling is visible in the boot.
Why it happens: Water enters through deteriorated taillight seals, boot seal, and rear hatch seal. It pools in the spare wheel well with nowhere to drain. Trapped moisture rusts the metal from both sides.
How to fix it: Replace taillight seals and boot/hatch seals first to stop water ingress. Cut out rusted metal and weld in repair panels. Reproduction spare wheel wells are available from specialist suppliers. Coat the repaired area with POR-15 and cavity wax the enclosed sections.
Severity: Needs attention. Does not directly affect structural integrity but indicates broader corrosion issues.
Rear Quarter Panel Rust
What happens: Rust appears behind the rear wheels, often starting as bubbles under the paint and progressing to perforations.
Why it happens: Road spray from the rear wheels is thrown against the inner guard, which is a double-skinned area that traps moisture. The outer skin rusts from the inside out.
How to fix it: Repair panels are available for the lower rear quarters. The job requires cutting out the affected area, treating the inner skin, and welding in the repair panel. This is panel-and-paint work, budget $1,500-3,000 per side for a professional repair.
Severity: Needs attention. Cosmetic but indicates moisture trapped in the body structure.
Engine
SU Carburettor Wear and Tuning Issues (240Z, 260Z)
What happens: Poor idle, hesitation on acceleration, rich or lean running, black smoke, poor fuel economy, difficult starting. The engine may run well at some RPMs but poorly at others.
Why it happens: The twin SU carburettors use a sliding piston (suction chamber) that rises and falls based on engine vacuum. Over decades, the throttle shafts wear in their bores, creating vacuum leaks that cannot be compensated for by adjustment. The needle and jet wear, the float valve leaks, and the damper oil evaporates. SU carburettors are precision instruments that require regular maintenance, and most Z-car SUs haven’t had it.
How to fix it: A full rebuild addresses all wear items: new throttle shaft bushings (if the bodies are not too worn), new needles, new jets, new float valves, new gaskets, and new damper oil (light machine oil, 20W). Cost: $400-800 in parts for a pair. Finding someone who can properly tune SU carburettors is increasingly difficult, this is a dying art. Alternatively, many owners convert to Weber DCOE sidedrafts ($1,500-3,000 for a pair with manifold) or electronic fuel injection (Haltech, Link, or MegaSquirt, $2,000-4,000 including sensors and wiring).
Severity: Needs attention. Carburettor issues make the car frustrating to drive but rarely strand you.
Fuel Injection Faults (280Z)
What happens: Hard starting (especially cold), rough idle, hesitation, rich or lean running, stalling. The engine management warning light may illuminate.
Why it happens: The Bosch L-Jetronic fuel injection system uses an airflow meter (AFM) with a mechanical flap that wears with age. The cold start injector and thermo time switch fail. Injector seals harden and leak. The electronic control unit (ECU) can develop dry solder joints. Wiring connectors corrode, creating intermittent faults.
How to fix it: Start with the basics: clean or replace the AFM ($200-500 used, very hard to source new), replace injector seals ($50-80 for a set), clean the cold start injector, test the thermo time switch, and inspect all wiring connectors for corrosion. For a permanent solution, many owners convert to modern aftermarket EFI, a Haltech or Link ECU with new injectors eliminates all age-related injection issues and makes the engine far more tuneable. Cost: $2,000-4,000 for a quality conversion.
Severity: Needs attention. Can leave you stranded if the AFM fails completely.
Timing Chain Stretch
What happens: Rattling or slapping noise from the front of the engine, particularly on cold start. The noise may diminish as the engine warms but does not fully disappear.
Why it happens: The L-series uses a single-row timing chain (on early engines) or double-row chain (later engines) with a hydraulic chain tensioner. Over time, the chain stretches and the tensioner guides wear. The tensioner compensates up to a point, but eventually the chain becomes excessively loose.
How to fix it: Replace the timing chain, tensioner, and guides. A double-row chain conversion kit is available for single-row engines ($200-400) and is strongly recommended. The job requires removing the radiator, fan, and timing cover. It is a full day’s work but well within the ability of a home mechanic. Do not ignore excessive chain noise, a severely stretched chain can jump a tooth, causing valve timing to shift and potentially causing valve-to-piston contact.
Severity: Needs attention. Becomes urgent if the chain is severely stretched.
Head Gasket Failure
What happens: Coolant loss with no visible external leak. White smoke from the exhaust. Milky residue on the oil filler cap. Overheating. Coolant in the oil or oil in the coolant.
Why it happens: The L-series head gasket is a composite design that deteriorates with age, thermal cycling, and overheating events. The long inline-six cylinder head is prone to distortion if overheated.
How to fix it: Replace the head gasket. The head must be removed and checked for flatness, have it machined if distorted (0.05 mm maximum distortion is the limit). While the head is off, replace the valve stem seals and inspect the cam and followers. Cost: $300-600 for parts (gasket set, head bolts, valve seals), plus machining ($150-300). A competent home mechanic can do this job in a weekend.
Severity: Urgent. Driving with a failed head gasket causes further overheating and accelerates engine damage.
Valve Stem Seal Deterioration
What happens: Blue-grey smoke on startup (after the car has been sitting). Blue smoke on deceleration (lifting off the throttle after sustained acceleration). Oil consumption increases, typically 1L per 2,000-3,000 km.
Why it happens: The original valve stem seals are rubber and harden with age, losing their ability to prevent oil from seeping past the valve stems into the combustion chambers.
How to fix it: Replace the valve stem seals. This can be done with the head in place using a valve spring compressor and compressed air to hold the valves up (feed air into the spark plug hole with a fitting). Cost: $50-100 for a seal set. The job takes 3-4 hours. If the car is consuming significantly more than 1L per 3,000 km, the valve guides may also be worn and require replacement (head must come off for this).
Severity: Minor annoyance if oil consumption is manageable. Needs attention if consumption is excessive.
Drivetrain
Rear Wheel Bearing Wear
What happens: Humming or grinding noise from the rear, increasing with speed. The noise may change tone when turning (loading one side more than the other).
Why it happens: The rear wheel bearings on Z-cars are a known wear item. They are tapered roller bearings that require periodic adjustment and eventually wear beyond the adjustment range.
How to fix it: Replace the rear wheel bearings. This requires a press to remove and install the bearings. The half-shaft must be removed, the bearing pressed off, and a new bearing pressed on. Cost: $100-200 per side in parts. Not a particularly difficult job but requires access to a press.
Severity: Needs attention. Severely worn bearings can seize, which is dangerous at speed.
Differential Mount Bushing Wear
What happens: Clunking from the rear on acceleration, deceleration, and gear changes. The clunk is felt through the car, not just heard.
Why it happens: The differential is mounted to the rear subframe with rubber bushings that perish with age. As the rubber deteriorates, the diff moves under load, causing the clunking.
How to fix it: Replace the diff mount bushings. Polyurethane replacement bushings are available and far more durable than the original rubber ($80-150 for a set). The job requires supporting the diff, removing the old mounts, and pressing in new bushings. Some owners upgrade to solid aluminium mounts for track use, but these transmit significantly more noise and vibration.
Severity: Needs attention. The clunking is annoying and the movement accelerates wear on the halfshaft universal joints.
Gearbox Synchro Wear (5-speed)
What happens: Grinding or crunching when shifting into 2nd or 3rd gear, particularly on quick shifts or cold starts.
Why it happens: The synchro rings wear with age and enthusiastic use. Second gear takes the most abuse in normal driving.
How to fix it: A gearbox rebuild with new synchro rings, bearings, and seals. Cost: $1,000-2,000 for parts and labour. Alternatively, a good used gearbox can be sourced for $500-1,000. The 280Z 5-speed is the strongest unit and the most desirable replacement.
Severity: Needs attention. Worn synchros get progressively worse if ignored.
Electrical
Earth/Ground Issues
What happens: Dim or flickering lights, erratic gauge readings, intermittent electrical faults that come and go. The engine may misfire or run poorly.
Why it happens: The Z-car uses a single-wire electrical system with the body as the return path (earth). Over 50 years, every earth point corrodes, increasing resistance and causing voltage drop. This affects everything from the headlights to the ignition system.
How to fix it: Clean every earth point on the car. There are approximately 15-20 earth points, on the engine block, body, dashboard, and rear. Sand the contact area back to bare metal, apply dielectric grease, and retighten. Adding supplementary earth straps (engine to firewall, body to battery) is cheap and effective insurance. Cost: virtually free. Time: 2-3 hours.
Severity: Needs attention. Poor earths cause a cascade of symptoms that can be maddeningly difficult to diagnose if you don’t start here first.
Wiring Harness Deterioration
What happens: Intermittent electrical faults, burnt connectors, melted wire insulation. In extreme cases, electrical fires.
Why it happens: The original wiring insulation becomes brittle with heat and age. Connectors corrode. Previous owners have spliced into the harness for accessories, often poorly.
How to fix it: Inspect the entire harness, paying particular attention to the engine bay (heat exposure) and the area behind the dashboard. Replace damaged sections. For a car undergoing restoration, a complete reproduction wiring harness is available from companies like Wiring Specialties ($600-1,200) and is well worth the investment.
Severity: Urgent if fire risk exists. Needs attention otherwise.
Combination Switch Failure
What happens: Turn signals, headlights, or wipers stop working intermittently or permanently.
Why it happens: The combination switch (stalk) on the steering column wears internally. The electrical contacts corrode and the plastic components crack.
How to fix it: Replace the combination switch. Used units are available from wreckers but may have the same wear. Reproduction units are available for some models ($150-300). Disassembly and cleaning of the internal contacts can sometimes restore function.
Severity: Needs attention. Non-functional indicators or headlights are a safety and registration issue.
Cooling System
Overheating
What happens: Temperature gauge climbs into the danger zone, particularly in traffic or on hot days. Coolant loss from the overflow.
Why it happens: Multiple factors compound on old Z-cars: a radiator that is partially blocked with scale, a thermostat that is stuck or partially open, a water pump with worn impeller, collapsed coolant hoses (the lower hose is most susceptible, it needs a spring insert to prevent collapse under suction), and a cooling fan that is not pulling sufficient air (the viscous clutch on the engine-driven fan wears out).
How to fix it: Address all components systematically. A new aluminium radiator ($300-600) with more capacity than the original brass unit is a worthwhile upgrade. Replace the thermostat ($20-30), water pump ($80-150), all coolant hoses ($100-200 for a complete set), and the fan clutch ($80-150). A thermo-fan conversion (electric fan with a thermal switch) is popular and frees up engine power. Cost: $200-400 for a quality setup.
Severity: Urgent. Overheating warps the head and destroys the head gasket.
Suspension
Worn Bushings (All Suspension Points)
What happens: Vague steering, clunking over bumps, wandering at highway speed, uneven tyre wear.
Why it happens: Every rubber bushing in the suspension is original and has exceeded its service life many times over. The control arm bushings, sway bar bushings, strut top mounts, and rear trailing arm bushings all deteriorate with age.
How to fix it: Replace all suspension bushings. A complete polyurethane bushing kit is available from companies like Energy Suspension and SuperPro ($400-800 for a full car set). This is a significant job, allow a weekend for a complete suspension refresh including new ball joints, tie rod ends, and shock absorbers. The result is transformative: a Z-car with fresh bushings handles like a completely different car.
Severity: Needs attention. Worn bushings compromise handling, braking, and safety.
Preventive Maintenance
To keep an L-series Z-car reliable:
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Change engine oil every 5,000 km using 10W-40 mineral or 15W-40 diesel-rated oil (the zinc content in diesel-spec oil protects the flat-tappet camshaft). Capacity: 4.3L (L24), 4.5L (L26/L28).
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Inspect and adjust valve clearances every 10,000 km. The L-series uses mechanical valve adjustment (no hydraulic lifters). Intake: 0.25 mm cold. Exhaust: 0.30 mm cold. Incorrect clearances cause poor running and accelerate cam wear.
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Replace coolant every 2 years. Use a quality green or blue coolant mixed 50/50 with distilled water. Flush the system thoroughly before refilling.
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Lubricate the SU carburettor dashpot pistons (240Z/260Z) with light machine oil (SAE 20W) every 5,000 km. Top up the damper oil regularly.
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Clean and check all earth points annually. This single task prevents more electrical headaches than anything else.
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Inspect the timing chain at every valve adjustment. Remove the timing cover inspection plate and check chain tension. Replace the chain before it becomes excessively loose.
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Treat and prevent rust aggressively. Cavity wax all box sections annually. Inspect the floors, sills, and strut towers at every service. Catching rust early saves thousands.
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