1987 Mercedes-Benz 420 — MOT failures & pass rate
Across 868 MOT tests, the 1987 Mercedes-Benz 420 recorded an 84.5% pass rate. That is 5.0 percentage points better than all cars of a similar age, which fail at 20.6%. Failures cluster in lighting & signalling, brakes and suspension.
What the MOT record shows
No single area dominates — lighting & signalling (8.8%) and brakes (6.2%) are close, so failures are spread across several systems rather than one weak point.
At component level the recurring items are ball joint dust cover, headlamp aim and service brake performance — ball joint dust cover alone was recorded 48 times.
Mileage is the strongest signal on the record: 6.5% of 30-60k cars fail, rising to 19.2% once past 150k — 2.9× the risk.
Advisories point at the next bill rather than this one: suspension was flagged on 20.3% of tests without failing them.
The trend is improving — the fail rate fell from 16.9% in 2021 to 15.0% in 2025, as the worst-kept examples leave the fleet.
How it compares
Top failure categories
| # | Category | % of tests affected | Tests |
|---|---|---|---|
| 1 | Lighting & signalling | 8.8% | 76 |
| 2 | Brakes | 6.2% | 54 |
| 3 | Suspension | 5.5% | 48 |
| 4 | Body, structure & corrosion | 3.6% | 31 |
| 5 | Visibility | 3.2% | 28 |
| 6 | Emissions & environmental | 3.2% | 28 |
Most common specific failures
The exact components most often recorded as failures — more specific than the categories above.
| # | Failure item | Times recorded |
|---|---|---|
| 1 | Ball joint dust cover | 48 |
| 2 | Headlamp aim | 45 |
| 3 | Service brake performance | 39 |
| 4 | Component mounting prescribed areas | 30 |
| 5 | Non catalyst emissions | 26 |
| 6 | Wipers | 19 |
Top advisory categories
Advisories aren't failures, but they flag work likely needed soon — useful when budgeting.
| # | Category | % of tests with advisory | Tests |
|---|---|---|---|
| 1 | Suspension | 20.3% | 176 |
| 2 | Emissions & environmental | 13.1% | 114 |
| 3 | Brakes | 12.7% | 110 |
| 4 | Body, structure & corrosion | 10.0% | 87 |
| 5 | Steering | 9.4% | 82 |
| 6 | Tyres | 9.0% | 78 |
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 | 107 | 6.5% |
| 60-90k | 265 | 11.7% |
| 90-120k | 261 | 19.9% |
| 120-150k | 117 | 21.4% |
| 150k+ | 99 | 19.2% |
Trend over time
| Dataset year | Tests | Fail rate |
|---|---|---|
| 2021 | 184 | 16.9% |
| 2022 | 183 | 13.7% |
| 2023 | 172 | 16.3% |
| 2024 | 169 | 16.0% |
| 2025 | 160 | 15.0% |
What to check before buying a 1987 420
On a 1987 420, lighting & signalling is what the MOT record says goes wrong most — it appeared in 8.8% of tests. Check these areas before you commit.
- 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.
- Brakes (6.2% of tests): Pads/discs are routine wear; binding, imbalance or corroded pipes are more serious — test for pulling under braking. Typical repair: £100–£350 per axle.
- Suspension (5.5% 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.
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 1987 Mercedes-Benz 420s pass their MOT?
84.5% of the 868 1987 Mercedes-Benz 420 MOT tests in this dataset passed — a 15.6% fail rate.
What is the most common MOT failure on a 1987 Mercedes-Benz 420?
Lighting & signalling, recorded in 8.8% of tests, followed by brakes (6.2%).
Does the 1987 420 get worse with mileage?
Its MOT fail rate rises from 6.5% in the 30-60k band to 19.2% in the 150k+ band.
Methodology & source. Based on 868 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.