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MG B Problems & Known Issues

The most common MG B problems ranked by severity — what to watch for, what it costs to fix, and what happens if you ignore it.

Generations

MK1 — MGB Mark 1
1962–1967
1.8 BMC B-Series
MK2 — MGB Mark 2
1967–1974
1.8 BMC B-Series
MK3 — MGB Mark 3 (Rubber Bumper)
1974–1980
1.8 BMC B-Series

Top issues to watch for

The most serious MG B problems ranked by severity. We track 5 known issues — here are the ones you need to know about first.

Dangerous
Structural corrosion compromising rigidity
MK1, MK2, MK31962–198020k–100k miles
The MGB monocoque construction uses steel prone to corrosion in structural areas including sills, floor pans, and bulkhead. Poor factory rustproofing and single-skin construction in critical areas make structural corrosion endemic on surviving examples. Areas of particular concern include inner and outer sills, rear wheel arch areas, and floor pan sections where water collects.
What happens if ignoredSevere structural corrosion renders the vehicle unsafe and unroadworthy. Professional restoration involving sill replacement, floor pan sections, and structural welding typically costs £3,000-£8,000 depending on extent. The car should not be driven if structural integrity is compromised.
Independent garage
£2,000–£5,000
Specialist
£3,000–£8,000
Parts only
£500–£1,500
Major
Excessive emissions levels
MK1, MK2, MK31962–19800k–100k miles
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. This reflects the carburetted fuel system design, worn engine internals affecting combustion efficiency, and the challenge of maintaining correct mixture on aged SU carburettors. The issue affects all mileage ranges and has been worsening in recent MOT data.
What happens if ignoredThe vehicle will fail MOT testing and cannot be legally driven on public roads until repaired. Professional carburettor setup and engine tuning typically resolves emissions issues. Severe cases may require engine internal work if compression is poor.
Independent garage
£150–£300
Specialist
£200–£400
Parts only
£50–£150
Major
Wheel bearing excessive play
MK1, MK2, MK31962–19800k–100k miles
MGB wheel bearings fail MOT testing for excessive play at 28.3 times the fleet average, with the trend worsening. The car uses traditional taper roller bearings front and rear that require periodic adjustment and lubrication. Age-related bearing wear combined with infrequent maintenance leads to dangerous wheel bearing play that affects steering precision and braking stability.
What happens if ignoredExcessive wheel bearing play creates dangerous driving conditions affecting steering control and braking performance. Severe play can lead to complete bearing collapse and wheel detachment. Professional bearing replacement and adjustment is required immediately.
Independent garage
£120–£200
Specialist
£150–£250
Parts only
£40–£80
Major
Suspension component excessive wear
MK1, MK2, MK31962–19800k–100k miles
MGB suspension components fail MOT testing at 50.4 times the fleet average with a worsening trend. The car uses kingpin front suspension and leaf spring rear suspension with rubber bushes throughout that deteriorate with age. Trunnions, kingpins, and suspension arm bushes are particular failure points that affect handling safety and MOT compliance.
What happens if ignoredWorn suspension components compromise vehicle handling, steering precision, and braking stability. The vehicle will fail MOT testing and may become dangerous to drive. Professional suspension overhaul including bushes, kingpins, and trunnions is typically required.
Independent garage
£400–£800
Specialist
£500–£1,000
Parts only
£150–£400

1 more known issues tracked

Including wear items, electrical niggles, and generation-specific problems.

MOT failure hotspots

Based on DVSA MOT test data. These are the items where the MG B fails at a significantly higher rate than the average car.

Light unit fault
Lights & Electrics · 0-20k miles
MOT failure rate: 584x the fleet average
Sample: 2,148 tests
Emissions failure
Exhaust & Emissions · 20-40k miles
MOT failure rate: 438x the fleet average
Sample: 1,794 tests
Transmission joint, belt or chain worn
Bodywork · 20-40k miles
MOT failure rate: 298x the fleet average
Sample: 1,339 tests
Wheel with a loose or missing wheel nut, bolt o...
Wheels · 0-20k miles
MOT failure rate: 222x the fleet average
Sample: 2,275 tests
Coil springs broken
Suspension · 20-40k miles
MOT failure rate: 100x the fleet average
Sample: 1,889 tests
Steering rack wear
Steering · 20-40k miles
MOT failure rate: 70x the fleet average
Sample: 2,948 tests

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MG B reliability FAQs

What are the most common problems with the MG B?

The MG B has 5 known issues across 3 severity levels. The most serious are: Structural corrosion compromising rigidity.

Is the MG B reliable?

The MG B has 1 dangerous and 3 major known issues. Most can be avoided with a thorough pre-purchase check and full service history.

How much does it cost to fix MG B problems?

Repair costs range widely. The most significant issue (Structural corrosion compromising rigidity) costs £2,000–£5,000 at an independent garage. Minor issues can be under £200. Always get a full inspection before buying.

Which MG B generation is most reliable?

The MK1 (1962–1967) has the fewest dangerous issues (1). However, condition and service history matter more than generation — a well-maintained earlier car can be more reliable than a neglected newer one.