MG Mgb MOT Failures
An analysis of 1,041 real DVSA MOT tests on the MG Mgb — what fails, how often, and how that compares to every other car on UK roads. Generations covered: MkI (1962–1967), MkII (1967–1969), MkIII (1969–1974), MkIV (1974–1980).
Where the MG Mgb fails its MOT
The single biggest MOT failure point on the MG Mgb is fluid leak — this model is 17 times more likely to fail on this item than the average car on UK roads. That makes it a significant weak point for anyone buying or owning this model. Across 1,041 MOT tests, 12.82% of all MG Mgb tests recorded this as a failure.
Exhaust and emissions failures often point to catalytic converter degradation, lambda sensor faults, or — in diesel models — DPF problems. These can be expensive to fix and will cause an immediate MOT failure.
Other notable weak points include wheel bearings worn (37x the fleet average), brake pipes corroded (8.3x the fleet average), and suspension pin, bush or joint worn (7.0x the fleet average). These ratios compare the MG Mgb's failure rate on each item against the national average for all cars tested — a ratio of 10x means this model fails ten times more often than a typical car.
The failures span 3 categories: Exhaust & Emissions, Suspension, Brakes. If you're inspecting a MG Mgb before purchase, these are the areas to focus on — and if any have been flagged as advisories on a previous MOT, they're likely to become failures in the near future.
Known issues beyond the MOT
An MOT only tests roadworthiness at a single point in time — it won't catch developing faults, intermittent problems, or issues that haven't yet reached the failure threshold. These are the issues that MG Mgb specialists and owners flag most frequently, drawn from manufacturer technical bulletins, workshop data, and verified owner reports.
Extensive body corrosion Dangerous
The MGB monocoque construction uses thin steel panels that corrode extensively in the British climate. Affects MkI, MkII, MkIII, MkIV; typical independent garage repair cost is £500–£2,000.
Overdrive unit failure Major
The Laycock de Normanville Type A overdrive unit fitted to many MGBs operates hydraulically using engine oil pressure. Affects MkII, MkIII, MkIV.
Lucas electrical system failures
MGB electrical systems use Lucas components including the notorious positive-earth charging system (pre-1967) and various switches, relays, and wiring looms of variable quality. Affects MkI, MkII, MkIII, MkIV; typical independent garage repair cost is £100–£400.
Twin SU carburettor imbalance and wear
All MGBs use twin SU carburettors (HS4 or HIF types depending on year) that require regular balancing to maintain smooth running. Affects MkI, MkII, MkIII, MkIV; typical independent garage repair cost is £80–£150.
For the complete picture — including repair costs across independent, specialist, and dealer garages — see the full MG Mgb common problems breakdown.
What to check before buying a MG Mgb
Based on the MOT failure data and known issues above, here's what to prioritise when inspecting a MG Mgb:
Exhaust & Emissions — check for fluid leak. Suspension — check for wheel bearings worn, suspension pin, bush or joint worn. Brakes — check for brake pipes corroded.
Beyond the MOT items, ask specifically about extensive body corrosion and overdrive unit failure. These won't show up on a standard MOT but can be expensive to fix — repairs start from £500. A specialist pre-purchase inspection is worth the investment on this model.
Always check the car's full MOT history for patterns — recurring advisories often become failures within 12 months. And verify the service history to confirm maintenance has been kept up to schedule. Enter any reg into our free car check to see the complete picture.
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MG Mgb MOT FAQs
What are the most common MOT failures on a MG Mgb?
Based on 1,041 DVSA MOT tests, the most common failure is fluid leak — at 17x the national fleet average. Other frequent failures include wheel bearings worn and brake pipes corroded.
Is the MG Mgb reliable based on MOT data?
The MG Mgb has 4 MOT failure categories above the fleet average. Specialists also flag extensive body corrosion as a concern. A pre-purchase inspection and service history check are recommended.
What MOT failures should I expect at high mileage?
The most common high-mileage failures include fluid leak, wheel bearings worn, brake pipes corroded.
How do I check a MG Mgb's MOT history?
Enter the registration number into our free car check above. You'll see every MOT test result, advisories and failures, mileage readings, write-off status, and finance checks.
MOT failure data sourced from DVSA bulk test records via data.gov.uk. Ratios compare this model's failure rate against the national fleet average. Known issues sourced from manufacturer bulletins, specialist workshops, and verified owner reports.