1986 Mercedes-Benz 420 — MOT failures & pass rate
The 1986 Mercedes-Benz 420 passed 82.0% of its 501 recorded MOT tests. That is 2.4 percentage points better than all cars of a similar age, which fail at 20.4%. Failures cluster in suspension, lighting & signalling and body, structure & corrosion.
What the MOT record shows
No single area dominates — suspension (8.8%) and lighting & signalling (8.8%) are close, so failures are spread across several systems rather than one weak point.
At component level the recurring items are component mounting prescribed areas, ball joint dust cover and headlamp aim — component mounting prescribed areas alone was recorded 32 times.
Mileage is the strongest signal on the record: 9.1% of 30-60k cars fail, rising to 23.5% once past 150k — 2.6× the risk.
Emissions & environmental is the most common advisory, noted on 17.2% of tests — work that passed today but is likely due soon.
How it compares
Top failure categories
| # | Category | % of tests affected | Tests |
|---|---|---|---|
| 1 | Suspension | 8.8% | 44 |
| 2 | Lighting & signalling | 8.8% | 44 |
| 3 | Body, structure & corrosion | 5.8% | 29 |
| 4 | Brakes | 5.6% | 28 |
| 5 | Emissions & environmental | 4.4% | 22 |
| 6 | Visibility | 4.0% | 20 |
Most common specific failures
The exact components most often recorded as failures — more specific than the categories above.
| # | Failure item | Times recorded |
|---|---|---|
| 1 | Component mounting prescribed areas | 32 |
| 2 | Ball joint dust cover | 30 |
| 3 | Headlamp aim | 27 |
| 4 | Non catalyst emissions | 19 |
| 5 | Integral vehicle structure condition | 16 |
| 6 | Wipers | 12 |
Top advisory categories
Advisories aren't failures, but they flag work likely needed soon — useful when budgeting.
| # | Category | % of tests with advisory | Tests |
|---|---|---|---|
| 1 | Emissions & environmental | 17.2% | 86 |
| 2 | Suspension | 16.6% | 83 |
| 3 | Brakes | 15.6% | 78 |
| 4 | Tyres | 7.6% | 38 |
| 5 | Body, structure & corrosion | 7.4% | 37 |
| 6 | Steering | 7.2% | 36 |
Failure rate by mileage
Higher-mileage cars tend to fail more — often the most useful guide to real condition.
| Mileage band | Tests | Fail rate |
|---|---|---|
| 30-60k | 66 | 9.1% |
| 60-90k | 150 | 19.3% |
| 90-120k | 104 | 15.4% |
| 120-150k | 105 | 21.9% |
| 150k+ | 68 | 23.5% |
Trend over time
| Dataset year | Tests | Fail rate |
|---|---|---|
| 2021 | 104 | 18.3% |
| 2022 | 105 | 21.9% |
| 2023 | 94 | 13.8% |
| 2024 | 98 | 16.3% |
| 2025 | 100 | 19.0% |
What to check before buying a 1986 420
The failure pattern for this year is specific enough to inspect against: suspension accounted for 8.8% of tests. Start there.
- Suspension (8.8% of tests): Worn drop links, bushes, springs or shocks — listen for knocks over bumps and check for uneven tyre wear. Typical repair: £150–£450 per corner.
- Lighting & signalling (8.8% of tests): Often a cheap bulb, but persistent issues can mean wiring or corrosion in the units. Typical repair: £10–£150.
- Body, structure & corrosion (5.8% of tests): The one to take seriously on older cars — corrosion to structural areas can be costly and is an MOT failure. Typical repair: £200–£1,500+.
Repair costs are rough UK ballpark ranges to set expectations, not quotes — actual prices vary widely by car, parts and garage.
Frequently asked questions
How many 1986 Mercedes-Benz 420s pass their MOT?
82.0% of the 501 1986 Mercedes-Benz 420 MOT tests in this dataset passed — a 18.0% fail rate.
What is the most common MOT failure on a 1986 Mercedes-Benz 420?
Suspension, recorded in 8.8% of tests, followed by lighting & signalling (8.8%).
Does the 1986 420 get worse with mileage?
Its MOT fail rate rises from 9.1% in the 30-60k band to 23.5% in the 150k+ band.
Methodology & source. Based on 501 MOT tests. Dataset: DVSA MOT testing data (2021,2022,2023,2024,2025). Data last updated 2026-07-27. Figures reflect MOT-testable defects only — read the methodology for how these are calculated and what they don't measure.