1986 Mercedes-Benz 300 — MOT failures & pass rate
Across 973 MOT tests, the 1986 Mercedes-Benz 300 recorded an 81.7% pass rate. All cars of a similar age fail 20.4% of the time, so this is 2.1pp better than the group it competes with. Failures cluster in lighting & signalling, suspension and brakes.
What the MOT record shows
No single area dominates — lighting & signalling (9.9%) and suspension (7.8%) 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 component mounting prescribed areas — ball joint dust cover alone was recorded 57 times.
Mileage is the strongest signal on the record: 17.0% of 30-60k cars fail, rising to 27.8% once past 150k.
Advisories point at the next bill rather than this one: suspension was flagged on 22.6% of tests without failing them.
The trend is improving — the fail rate fell from 19.9% in 2021 to 17.7% in 2025, as the worst-kept examples leave the fleet.
How it compares
Top failure categories
| # | Category | % of tests affected | Tests |
|---|---|---|---|
| 1 | Lighting & signalling | 9.9% | 96 |
| 2 | Suspension | 7.8% | 76 |
| 3 | Brakes | 5.2% | 51 |
| 4 | Body, structure & corrosion | 4.2% | 41 |
| 5 | Visibility | 3.7% | 36 |
| 6 | Emissions & environmental | 3.7% | 36 |
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 | 57 |
| 2 | Headlamp aim | 47 |
| 3 | Component mounting prescribed areas | 41 |
| 4 | Position lamp | 29 |
| 5 | Chassis condition | 25 |
| 6 | Integral vehicle structure condition | 25 |
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 | 22.6% | 220 |
| 2 | Brakes | 17.8% | 173 |
| 3 | Emissions & environmental | 16.9% | 164 |
| 4 | Body, structure & corrosion | 11.7% | 114 |
| 5 | Steering | 10.5% | 102 |
| 6 | Tyres | 9.8% | 95 |
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 | 147 | 17.0% |
| 60-90k | 273 | 14.6% |
| 90-120k | 249 | 17.3% |
| 120-150k | 194 | 19.6% |
| 150k+ | 90 | 27.8% |
By fuel type
| Fuel | Tests | Fail rate |
|---|---|---|
| Petrol | 853 | 17.2% |
| Diesel | 120 | 25.8% |
Trend over time
| Dataset year | Tests | Fail rate |
|---|---|---|
| 2021 | 201 | 19.9% |
| 2022 | 202 | 16.3% |
| 2023 | 190 | 16.3% |
| 2024 | 199 | 21.1% |
| 2025 | 181 | 17.7% |
What to check before buying a 1986 300
On a 1986 300, lighting & signalling is what the MOT record says goes wrong most — it appeared in 9.9% of tests. Check these areas before you commit.
- Lighting & signalling (9.9% of tests): Often a cheap bulb, but persistent issues can mean wiring or corrosion in the units. Typical repair: £10–£150.
- Suspension (7.8% 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.
- Brakes (5.2% 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.
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 300s pass their MOT?
81.7% of the 973 1986 Mercedes-Benz 300 MOT tests in this dataset passed — a 18.3% fail rate.
What is the most common MOT failure on a 1986 Mercedes-Benz 300?
Lighting & signalling, recorded in 9.9% of tests, followed by suspension (7.8%).
Does the 1986 300 get worse with mileage?
Its MOT fail rate rises from 17.0% in the 30-60k band to 27.8% in the 150k+ band.
Methodology & source. Based on 973 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.