IsItAGoodCar
Reliability Guide

Common Problems with the
1973–1974 Daimler Double Six

We've identified 3 known issues that can affect the 1973–1974 Daimler Double Six. 2 of these are serious faults that could be expensive to repair.

3
Known Issues
2
Serious
1
Moderate
0
Minor

All Known Issues

V12 Cooling System Silt Accumulation, Radiator Furring and Dropped Valve Seats

SeriousCooling System

The Jaguar all-aluminium V12 requires meticulous cooling maintenance due to its massive heat output and 20 individual coolant hoses. Neglected coolant changes allow mineral silt and corrosion sediment to clog the lower tubes of the cross-flow radiator and rear cylinder water passages. When localized overheating occurs, the aluminium cylinder head expands faster than the pressed-in steel valve seat inserts. Once press-fit tolerance is lost during extreme heat cycling, a valve seat insert loosens and drops into the combustion chamber, destroying the piston and bending valves. Remedying dropped seats requires an engine-out rebuild and peening or staking replacement inserts.

Est. Repair Cost: £1,800–£4,500
Warning Signs:

Temperature gauge needle creeping into the upper third or red sector in slow traffic, Loud metallic clicking or sudden violent knocking noise from the top of the cylinder head, Sudden severe misfire on one cylinder accompanied by complete compression loss, Coolant blowing past the expansion tank pressure cap after switching off the hot engine

What to Inspect:
  • Scan the radiator matrix with an infrared thermometer to detect cold, silted lower zones
  • Inspect coolant for clean 50/50 ethylene glycol mix and absence of rusty sediment
  • Verify that both the mechanical engine-driven fan clutch and auxiliary electric fan engage
  • Listen carefully with a mechanic's stethoscope for valve train ticking along the rear head banks
Verified by IsItAGoodCar Research TeamUpdated

Magneti Marelli and Lucas Ignition Amplifier / Distributor Rotor Breakdown

SeriousElectrics & Electronics

Late Daimler Double Six models utilise a Magneti Marelli dual-coil digital ignition system, while earlier cars feature Lucas OPUS or Constant Energy systems. On Marelli-equipped models, high secondary ignition resistance from aged spark plugs or degraded HT leads causes internal electrical arcing through the distributor rotor body directly to the distributor drive shaft. This burns a pinhole through the rotor, killing spark to an entire six-cylinder bank. Because the fuel injectors continue spraying fuel into the dead cylinders, raw petrol floods into the catalytic converter, causing it to overheat, glow red-hot, and ignite underbody fires. Regular rotor and cap renewal is mandatory.

Est. Repair Cost: £350–£900
Warning Signs:

Sudden 50 percent loss of engine power, leaving the car struggling to maintain 50 mph, Strong smell of unburned petrol and smoke rising from the catalytic converters underneath, Rough, lumpy idle with the engine running on only six cylinders instead of twelve, Glowing red exhaust downpipes or catalytic converters visible under the floorpan

What to Inspect:
  • Inspect the distributor rotor underneath for burnt carbon tracking or pinhole burns to earth
  • Check condition and resistance of all 12 spark plug leads and the two coil-to-distributor leads
  • Inspect catalytic converters and underbody heat shields for heat discoloration or melting
  • Examine Lucas ignition amplifier modules mounted on the hot intake manifold for heat paste drying
Verified by IsItAGoodCar Research TeamUpdated

Inboard Rear Brake Caliper Heat Seizure and Differential Output Seal Leaks

ModerateBrakes

On Series 1, 2, and 3 Double Six saloons, the independent rear suspension mounts the brake calipers and discs inboard against the Salisbury differential casing. The intense radiant heat generated by the heavy V12 powertrain and exhaust pipes bakes the caliper piston seals and differential output shaft seals. Hardened diff seals allow hypoid gear oil to leak directly onto the inboard brake discs and pads, drastically reducing stopping power. Concurrently, caliper pistons seize in their bores from heat and moisture accumulation, causing severe brake drag. Rectifying the assembly requires lowering the complete rear axle subframe.

Est. Repair Cost: £700–£1,600
Warning Signs:

Severe loss of rear braking effort and MOT brake roller test imbalance failure, Brake pedal feeling spongy with excessive travel before retarding the vehicle, Smoke and burning gear oil smell wafting from underneath the rear differential, Handbrake lever pulling to the top of its travel without holding the car firmly

What to Inspect:
  • Inspect the differential carrier casing for oil weeping around the brake disc flanges
  • Check inboard rear brake pads with a torch for oil soaking and glazing
  • Verify whether the complete rear subframe was dropped for recent brake servicing
  • Ensure that the handbrake tree mechanism operates smoothly without sticking
Verified by IsItAGoodCar Research TeamUpdated

Buying Tips for 1973–1974 Daimler Double Six

  • Inspect every rubber fuel hose across the engine valley and fuel rail immediately; dried-out hoses spraying fuel onto hot exhaust manifolds cause catastrophic fires.
  • Check coolant cleanliness and radiator core temperature across the entire surface using an infrared thermometer; silting leads to localized overheating and dropped valve seats.
  • Verify distributor cap and rotor condition on Marelli and Lucas ignition systems; internal rotor flashover cuts spark on one bank while raw fuel ignites in catalytic converters.
  • Inspect inboard rear brake calipers and differential output seals on Series 1 to 3 cars; gear oil weeping onto hot inboard discs ruins braking power and presents an MOT failure.
19721975–1980
Check a 1973–1974 Daimler Double Six by Registration