MOT Brake Test Explained: How Are Brakes Tested?

When a vehicle goes through its MOT, the brakes are one of the areas under close examination. But an MOT brake test is not simply a case of pressing the pedal and checking that the vehicle stops.

The test is designed to assess whether the braking system is performing effectively and whether any defects could affect the vehicle's ability to brake safely.

For workshops and technicians, understanding what the MOT brake test is actually measuring can also help explain why apparently small brake issues can result in a failure.

What happens during an MOT brake test?

For most cars and light commercial vehicles, braking performance is assessed using a roller brake tester.

The vehicle's wheels are placed on rollers which rotate the wheels while the brakes are applied. The equipment measures the braking force produced at each wheel and uses those measurements to assess the vehicle's braking performance.

Two things are particularly important: brake efficiency and brake imbalance.

Brake efficiency considers whether the vehicle is capable of producing sufficient braking force overall. Brake imbalance looks at the difference in braking effort between the wheels on the same axle.

A vehicle may have brakes that are working but still fail the test if braking performance is significantly uneven.

Fitting brand new pads just before the MOT can result in failure as the pads have not been bedded in, prior to the test. So it is essential to run a bed-in procedure prior to the MOT test.

To assist in this all Juratek pads for front applications, have a special performance improvement strip applied to assist in bedding the pads in quicker.  

Why is brake imbalance checked?

Braking needs to be consistent across an axle.

If one wheel brakes significantly harder than the other, the vehicle can become unstable under braking, particularly when the driver has to brake heavily.

Brake imbalance can have several causes. Uneven brake pad wear, a sticking or seized caliper, differences in friction between components or problems elsewhere in the braking system can all affect how braking force is distributed.

This is one reason an MOT failure shouldn't automatically be treated as a case of simply replacing whichever component looks most worn.

The cause of the imbalance needs to be understood.

What brake problems can cause an MOT failure?

The MOT inspection looks at the condition and performance of the braking system, rather than simply checking whether the vehicle has enough brake pad material remaining.

Depending on the severity, defects can include excessive wear, damage, corrosion, insecure components, leaking hydraulic components and problems affecting brake performance.

Brake discs can also be affected by excessive corrosion, cracking, damage or wear. Brake pads are assessed for issues including excessive wear and insecure or damaged components.

The important point is that brake component condition and brake performance are closely connected. A component might look acceptable at first glance but still contribute to poor or uneven braking.

Do worn brake pads always fail an MOT?

Not necessarily.

Brake pad wear is assessed against the condition and requirements set out in the MOT inspection manual. A pad does not automatically cause an MOT failure simply because it has been used or has visible wear.

However, excessively worn, damaged or insecure brake pads can result in a defect being recorded.

Uneven wear is also worth investigating. If the inner and outer pads are wearing at noticeably different rates, for example, there may be an issue with caliper movement or another part of the braking system.

For technicians, the MOT can therefore provide a useful indication that further investigation is needed rather than simply identifying a component for replacement.

And what about brake discs?

Brake discs naturally experience wear throughout their service life. They are exposed to friction, heat, moisture and road contamination every time the vehicle is driven.

Some surface corrosion is not unusual, particularly after a vehicle has been parked in damp conditions. The MOT inspection is concerned with corrosion or deterioration where it has become significant enough to affect the disc or braking performance.

Cracking, excessive wear and serious deterioration can also result in a defect.

This is why brake discs should be assessed alongside the pads rather than considered separately. The two components work together, and the condition of one can influence the performance and wear of the other.

What happens after a brake-related MOT failure?

If a vehicle fails its MOT because of a brake defect, the underlying cause should be identified before replacement parts are fitted.

For example, replacing an unevenly worn brake pad without investigating why it has worn unevenly may simply result in the same problem returning.

The same applies to discs, calipers and other braking components. Correct diagnosis and fitting are essential to restoring the braking system to the required standard.

The MOT is also only a snapshot of vehicle condition on the day of the test. It should not replace routine inspection and maintenance throughout the year.