1978 Mercedes 420 MOT Pass Rate
Pass rate for 420 models manufactured in 1978, based on 32 real MOT test results.
Data from official DVSA MOT testing records
1978 Mercedes 420 MOT Analysis
The 1978 Mercedes 420 has an MOT pass rate of 40.6% based on 32 tests — significantly below the UK average for UK vehicles. Cars of this vintage present for MOT with an average of 119,838 miles on the odometer. With a 59.4% failure rate, the 1978 420 is rated as "Very Poor" for MOT reliability.
The leading cause of MOT failure for the 1978 Mercedes 420 is Lamps, reflectors and electrical equipment, responsible for 21.9% of failures. Lighting failures cover all external lights: headlights, tail lights, brake lights, indicators, fog lights, and reflectors. A single blown bulb will cause an MOT fail. This is one of the most preventable failure categories. Typical repair costs range from £5–50. Suspension is the second most common issue at 18.8%. Body, chassis, structure follows at 15.6%.
Top failures specific to 1978 models only. The overall 420 page may show different rankings.
What Fails Most
What Fails on This Car?
Click a category to see specific failure items.
View as table
| Rank | Failure Category | Rate (%) | Count |
|---|---|---|---|
| 1 | Lamps, Reflectors And Electrical Equipment | 21.9% | 7 |
| 2 | Suspension | 18.8% | 6 |
| 3 | Body, Chassis, Structure | 15.6% | 5 |
| 4 | Brakes | 12.5% | 4 |
| 5 | Noise, Emissions And Leaks | 9.4% | 3 |
| 6 | Tyres | 6.3% | 2 |
| 7 | Visibility | 6.3% | 2 |
| 8 | Steering | 6.3% | 2 |
Failures per 10,000 Miles
avg. 119,838 miFor every 10,000 miles driven, this shows what percentage of MOT tests fail for each category. This accounts for how far cars are actually driven, not just raw pass/fail counts.
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| Category | Rate / 10K mi | Raw % | Count |
|---|---|---|---|
| Lamps & Electrical | 1.83 | 21.9% | 7 |
| Suspension | 1.56 | 18.8% | 6 |
| Body & Structure | 1.30 | 15.6% | 5 |
| Brakes | 1.04 | 12.5% | 4 |
| Noise, emissions and leaks | 0.78 | 9.4% | 3 |
| Tyres | 0.52 | 6.3% | 2 |
| Visibility | 0.52 | 6.3% | 2 |
| Steering | 0.52 | 6.3% | 2 |
Mileage Statistics
Mileage-adjusted failure rate — accounts for how much this model year is typically driven.
About This Data
The 1978 Mercedes 420 has an MOT pass rate of 40.6% based on 32 tests — significantly below the UK average for UK vehicles. Cars of this vintage present for MOT with an average of 119,838 miles on the odometer. With a 59.4% failure rate, the 1978 420 is rated as "Very Poor" for MOT reliability.
If you own or are considering buying a 1978 Mercedes 420, be prepared for above-average maintenance costs. Before your MOT, pay particular attention to lamps, reflectors and electrical equipment: Walk around the car and check every light — headlights (dipped and main beam), side lights, tail lights, brake lights, indicators, hazard lights, reverse light, rear fog light, and number plate lights. Replace any blown bulbs before the test. With an average mileage of 119,838 miles, these vehicles are in the higher-mileage bracket where wear-related failures become more common.
Lamps, reflectors and electrical equipment — 21.9% of failures
Lamps, reflectors and electrical equipment issues account for 21.9% of MOT failures on 1978 Mercedes 420 models. Lighting failures cover all external lights: headlights, tail lights, brake lights, indicators, fog lights, and reflectors. A single blown bulb will cause an MOT fail. This is one of the most preventable failure categories. Typical repair costs: £5–50. Pre-MOT check: Walk around the car and check every light — headlights (dipped and main beam), side lights, tail lights, brake lights, indicators, hazard lights, reverse light, rear fog light, and number plate lights. Replace any blown bulbs before the test.
Suspension — 18.8% of failures
Suspension issues account for 18.8% of MOT failures on 1978 Mercedes 420 models. Suspension failures typically involve worn bushes, leaking shock absorbers, broken coil springs, and damaged suspension arms. These affect ride quality, tyre wear, and road holding. Typical repair costs: £200–500. Pre-MOT check: Look for uneven tyre wear, listen for clunking over bumps, and check if the car pulls to one side. A bouncy ride suggests worn shock absorbers. Visually inspect coil springs for cracks.
Body, chassis, structure — 15.6% of failures
Body, chassis, structure issues account for 15.6% of MOT failures on 1978 Mercedes 420 models. Body and structure failures include excessive corrosion, sharp edges, loose panels, and damage to the vehicle frame. Rust is the primary concern, especially on older vehicles or those exposed to road salt. Typical repair costs: £100–500+. Pre-MOT check: Inspect sills, wheel arches, door bottoms, and the chassis for rust. Surface rust is acceptable but structural corrosion or holes will fail. Check that all doors, bonnet, and boot close securely.
Based on DVSA anonymised MOT test data (2005–2024). Crown copyright, Open Government Licence v3.0.