MG B MOT Failures

An analysis of 56,938 real DVSA MOT tests on the MG B — what fails, how often, and how that compares to every other car on UK roads. Generations covered: MK1 (1962–1967), MK2 (1967–1974), MK3 (1974–1980).

Where the MG B fails its MOT

The single biggest MOT failure point on the MG B is emissions failure — this model is 438 times more likely to fail on this item than the average car on UK roads. That makes it an extreme outlier for anyone buying or owning this model. Across 56,938 MOT tests, 0.81% of all MG B 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 coil springs broken (100x the fleet average), transmission joint, belt or chain worn (298x the fleet average), steering rack wear (70x the fleet average), and stop lamps all missing or inoperative (44x the fleet average). These ratios compare the MG B'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 6 categories: Exhaust & Emissions, Suspension, Bodywork, Steering, Lights & Electrics and others. If you're inspecting a MG B 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.

How failures change with mileage

The MG B's weak points shift as the car covers more miles. Understanding these patterns helps you know what to expect — and what to budget for — at each stage of ownership.

Under 60,000 miles

At this mileage, most failures are either design-related or caused by age rather than wear. Components like bushes and drop links may not have been replaced yet, and original-fit parts can deteriorate even on low-mileage cars that spend a lot of time sitting.

For the MG B specifically, the DVSA data shows the most common failures at this mileage are light unit fault (584x the average) and wheel with a loose or missing wheel nut, bolt o... (222x). emissions failure (101x) and transmission joint, belt or chain worn (80x) also appear frequently.

60,000 to 100,000 miles

This is where routine wear items start to show up. Brake components, tyres, and exhaust parts have done serious work by this point. Cars that have been well serviced will show fewer of these failures — this mileage band is where good maintenance really separates the well-kept from the neglected.

For the MG B specifically, the DVSA data shows the most common failures at this mileage are emissions failure (174x the average) and transmission joint, belt or chain worn (38x). coil springs broken (33x) and steering rack wear (21x) also appear frequently.

The shift from light unit fault at lower mileages to emissions failure at higher mileages is typical — early failures tend to be design or factory-related, while high-mileage failures reflect accumulated mechanical wear. A car that's been well maintained will usually dodge the worst of both.

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 B specialists and owners flag most frequently, drawn from manufacturer technical bulletins, workshop data, and verified owner reports.

Structural corrosion compromising rigidity Dangerous

The MGB monocoque construction uses steel prone to corrosion in structural areas including sills, floor pans, and bulkhead. Affects MK1, MK2, MK3; typical independent garage repair cost is £2,000–£5,000.

Excessive emissions levels Major

The BMC B-Series engine in MGBs consistently fails MOT emissions tests at 199.3 times the fleet average, the highest failure rate in the MOT statistical data. Affects MK1, MK2, MK3; typical independent garage repair cost is £150–£300.

Wheel bearing excessive play Major

MGB wheel bearings fail MOT testing for excessive play at 28.3 times the fleet average, with the trend worsening. Affects MK1, MK2, MK3; typical independent garage repair cost is £120–£200.

Suspension component excessive wear Major

MGB suspension components fail MOT testing at 50.4 times the fleet average with a worsening trend. Affects MK1, MK2, MK3; typical independent garage repair cost is £400–£800.

For the complete picture — including repair costs across independent, specialist, and dealer garages — see the full MG B common problems breakdown.

What to check before buying a MG B

Based on the MOT failure data and known issues above, here's what to prioritise when inspecting a MG B:

Exhaust & Emissions — check for emissions failure. Suspension — check for coil springs broken, suspension pin, bush or joint worn. Bodywork — check for transmission joint, belt or chain worn. Steering — check for steering rack wear.

Beyond the MOT items, ask specifically about structural corrosion compromising rigidity and excessive emissions levels. These won't show up on a standard MOT but can be expensive to fix — repairs start from £2,000. 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.

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.