NCT brake test failure: what to do next
Why the NCT brake test fails cars that 'feel fine', and how to fix it before the re-test.
The NCT brake test isn’t a road test — it’s a roller-brake test that measures braking force on each wheel and the difference between left and right. Cars that “feel fine” can still fail it. Here’s why, and what to do.
What the brake roller actually measures
Each wheel runs on a roller turning at a low speed; the brake is applied; sensors measure how much force each wheel resists with. The test fails the car if:
- Total braking efficiency is below the minimum (typically 50% for service brake, 16% for hand-brake)
- Imbalance between left and right on the same axle exceeds about 30%
- Hand-brake efficiency is below the minimum or imbalanced
Crucially: even cars with new pads can fail if one side is sticking, or if brake fluid is contaminated and the master cylinder is dragging slightly.
Common causes of brake test failure
- Sticking front caliper. Single most common. Caliper slide pins seize from corrosion; one side bites harder, the other lags. Strip-and-clean, regrease, refit — sometimes a new caliper.
- Worn pads on one side only. Sticking caliper from above; or a hose collapsing internally on one side. Replace pads, replace hose if needed.
- Glazed disc surface. Mostly city-driving cars — pads polish the disc instead of biting. Skim the disc or replace.
- Hand-brake cable stretched. Car parks fine but the lever travels too far. Cable adjustment or replacement.
- Brake fluid hygroscopic failure. Old fluid absorbs water, drops boiling point, and can cause spongy pedal under repeated braking. Fluid renewal every 2 years is the manufacturer schedule.
What we do at V.T. Motors after a brake test fail
You bring us the failure sheet. We strip both fronts (and rears if specified), measure pad and disc thickness, free off the calipers, replace any failed component, renew fluid if it’s old. Then we run the car on our four-wheel chassis dyno and confirm the imbalance is gone before you return for re-test.
Book brake repair — from €110, full quote on inspection. Phone 01 847 5146.