Triumph Stag MOT Failures

An analysis of 19,302 real DVSA MOT tests on the Triumph Stag — what fails, how often, and how that compares to every other car on UK roads. Generations covered: MK1 (1970–1977).

Where the Triumph Stag fails its MOT

The single biggest MOT failure point on the Triumph Stag is wheel bearings worn — this model is 63 times more likely to fail on this item than the average car on UK roads. That makes it a major concern for anyone buying or owning this model. Across 19,302 MOT tests, 12.76% of all Triumph Stag tests recorded this as a failure.

Suspension failures typically mean worn bushes, drop links, or dampers. These affect handling and tyre wear. Budget £150–£400 per corner at an independent garage for full suspension overhaul.

Other notable weak points include emissions failure (335x the fleet average), excessive radial movement between the top of th... (242x the fleet average), fluid leak (45x the fleet average), and power steering fault (112x the fleet average). These ratios compare the Triumph Stag'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 4 categories: Suspension, Exhaust & Emissions, Steering, Lights & Electrics. If you're inspecting a Triumph Stag 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 Triumph Stag'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 Triumph Stag specifically, the DVSA data shows the most common failures at this mileage are excessive radial movement between the top of th... (177x the average) and power steering fault (112x). emissions failure (108x) and free play in the steering, measured at the rim ... (51x) 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 Triumph Stag specifically, the DVSA data shows the most common failures at this mileage are emissions failure (114x the average) and excessive radial movement between the top of th... (95x). power steering fault (26x) and steering rack wear (26x) also appear frequently.

The shift from excessive radial movement between the top of th... 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 Triumph Stag specialists and owners flag most frequently, drawn from manufacturer technical bulletins, workshop data, and verified owner reports.

Steering Column Top Bearing Wear Dangerous

The steering column top bearing on the Stag suffers from excessive wear, creating dangerous radial movement between the steering wheel and column shaft. Affects MK1; typical independent garage repair cost is £200–£400.

Engine Overheating Major

The Stag's alloy V8 engine is notoriously prone to overheating due to poor cooling system design and inadequate radiator capacity for the engine's heat output. Affects MK1.

Timing Chain Wear Major

The Stag V8 uses duplex timing chains that stretch with age and mileage, causing timing retardation and characteristic rattling from the timing case. Affects MK1.

Power Steering System Failure Major

The Stag's power steering system suffers from widespread pump and seal failures, with MOT data showing this model fails at 111.7 times the fleet average for power steering malfunctions. Affects MK1; typical independent garage repair cost is £300–£600.

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

What to check before buying a Triumph Stag

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

Suspension — check for wheel bearings worn, abs fault. Exhaust & Emissions — check for emissions failure, fluid leak. Steering — check for excessive radial movement between the top of th..., power steering fault, free play in the steering, measured at the rim ....

Beyond the MOT items, ask specifically about steering column top bearing wear and engine overheating. These won't show up on a standard MOT but can be expensive to fix — repairs start from £200. 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.