MOT Test of Brakes (1)
Efficiency and balance of brakes is usually checked on a roller brake tester. In certain cases where a roller brake tester may not be used (for example on certain 4-wheel drive vehicles) it may be necessary to check brake efficiency and balance on a road test, with a portable decelerometer (pictured below).
A decelerometer will be placed in the vehicle while the Tester conducts a road test to check brake efficiency (The instrument would normally be placed on the floor of the vehicle during the Test).Mechanical components
Unsurprisingly as a major vehicle safety system, the MOT inspection of vehicles’ brakes is extensive and complex. Whilst we have looked into this in some detail here, the key point is that all mechanical braking components that a Tester can see, from under the bonnet, from inside the vehicle, or from beneath the vehicle, will need to be inspected for wear and condition.
Inside the car
Anti-lock braking system (if fitted) warning lamp is checked for:
- function
- sequence of operation
Footbrake
A fail applies if:
- there’s insufficient reserve travel on the footbrake(ie, it touches the floor)
- the brake pedal rubber is excessively worn*
- incorrect operation of the servo assistance system
- unacceptable wear on the brake pedal pivot
Service brake pedal or hand lever condition and travel
*A brake pedal rubber is an anti-slip material and it is therefore not regarded as a defect if it’s worn smooth.
A brake pedal without a rubber usually has grooves or raised sections to provide grip in wet conditions and should be rejected if it’s worn smooth. However, some vehicles may have been manufactured with a brake pedal which did not incorporate grooves or the fitting of an anti-slip material and these will not be rejected.
A brake pedal will fail if its grooves or raised grip sections are worn smooth. However, it will not be a fail if the vehicle has been manufactured with one that doesn’t have grooves or anti-slip material.
Often a vehicle is fitted with an aftermarket brake pedal rubber. It isn’t a defect if the design pattern of the brake pedal rubber is worn smooth.
A vehicle should only be failed for insufficient reserve if the pedal or lever is touching the floor/handlebar. Checks on vehicles with power-assisted braking systems should be carried out with the engine off.
The following categories apply to defects in this section:
| Defect | Category |
|---|---|
| a. Insufficient reserve travel | Major |
| b. Service brake control: i. not releasing correctly | Minor |
| ii. functionality of brakes affected | Major |
| c. Anti-slip provision missing, loose or worn smooth | Major |
Parking brake (‘handbrake’)
This could be hand, foot or electronically operated. Checked for reserve travel so that it doesn’t reach the stops on application. The parking brake lever’s mountings will be checked for security and/or corrosion. On electronic systems a parking brake warning light illuminated is a failure.
A parking brake lever must have obvious excessive travel before being rejected.
The following categories apply to defects in this section:
| Defect | Category |
|---|---|
| a. Ratchet not holding correctly | Major |
| b. Parking brake lever pivot or ratchet mechanism: i. obviously worn | Minor |
| ii. worn to the extent that the brake may inadvertently release | Major |
| c. Parking brake lever has excessive movement indicating incorrect adjustment | Major |
| d. Parking brake control missing, defective or inoperative | Major |
| e. Electronic parking brake MIL indicates a malfunction | Major |
| f. Parking brake is not capable of being maintained in operation by direct mechanical action only (vehicle first used on or after 1 January 1968) | Major |
Under bonnet checks
The MOT inspection requires the following checks of systems accessible within the vehicle’s engine compartment for the majority of vehicles:
- master cylinder and servo unit are checked for leaks with the engine on and the brakes applied
- servo unit will be checked to ensure it is operating correctly*
- visible metal or flexible brake pipes will be checked for corrosion, condition, fouling or leaks
*Note: This can be checked by depressing the brake pedal with the engine running and switching off the ignition – a slight increase in the of pressure on the pedal indicates the servo is working.
Brake servo units and master cylinder (hydraulic systems)
Hydraulic brake fluid level checks are confined to transparent reservoirs or where an indicator is fitted. Reservoir caps shouldn’t be removed.
A brake fluid warning lamp may be shared with other components, for example to indicate that brake pads are worn or the parking brake is applied. Class 3 vehicles aren’t inspected for brake fluid warning lamp.
The following categories apply to defects in this section:
| Defect | Category |
|---|---|
| a. Brake servo: i. defective or ineffective | Major |
| ii. inoperative | Dangerous |
| b. Master cylinder: i. defective but brakes still operating | Major |
| ii. leaking | Dangerous |
| c. Master cylinder insecure | Major |
| d. Brake fluid: i. below minimum mark | Minor |
| ii. significantly below minimum mark | Major |
| iii. not visible | Dangerous |
| e. Master cylinder reservoir cap missing | Major |
| f. Brake fluid warning light illuminated or defective | Minor |
| g. incorrect functioning of brake fluid level warning device | Minor |
Under vehicle checks
- flexible brake pipes and any other metal brake pipes visible beneath the car are checked
- discs and drums (external only) checked for condition and contamination
- brake back plates and caliper securing devices are checked for condition and security
- condition of the brake pads will be checked if visible
- The assistant operates the handbrake and the condition of the linkages and/or cables is checked.
- on some vehicles there will be a brake compensating valve beneath the car which will need to be inspected for fluid leaks
Rigid brake pipes
Chafing, corrosion or damage to a rigid brake pipe so that its wall thickness is reduced by 1/3 (approximately 0.25 mm for typical hydraulic brake pipe) will fail. As it is sometimes difficult to assess this accurately, if not sure, the Tester will give the benefit of the doubt.
The following categories apply to defects in this section:
| Defect | Category |
|---|---|
| a. Brake pipe is at imminent risk of failure or fracture | Dangerous |
| b. Leaking brake pipe or connection: i. on an air brake system | Major |
| ii. on a hydraulic system | Dangerous |
| c. Brake pipe damaged or excessively corroded | Major |
| d. Brake pipe: i. inadequately clipped or supported | Minor |
| ii. likely to become detached or damaged | Major |
Flexible brake hoses
A hose which is damaged or chafed severely enough to expose the reinforcement will be rejected.
The following categories apply to defects in this section:
| Defect | Category |
|---|---|
| a. Brake hose damaged and likely to fail | Dangerous |
| b. Flexible brake hose: i. slightly damaged, chafed or twisted | Minor |
| ii. excessively damaged, chafed, twisted or stretched | Major |
| c. Brakes, hoses or connections leaking on: i. air brake systems | Major |
| ii. hydraulic systems | Dangerous |
| d. Brake hose bulging under pressure | Major |
| e. Brake hose porous | Major |
| b. Brake hose ferrules: i. excessively corroded | Major |
| ii. excessively corroded and likely to fail | Dangerous |
Brake linings and pads
Some vehicles have a warning light on the dashboard to indicate that the brake pads are becoming excessively worn. Sometimes this lamp is shared with other components, such as to show that the handbrake is applied. If the warning light is lit, the Tester will fail it, unless it can be seen that there is another reason for it being lit.
The following categories apply to defects in this section:
| Defect | Category |
|---|---|
| a. Brake lining or pad: i. worn down to wear indicator | Major |
| ii. worn below 1.5mm | Dangerous |
| b. Brake lining or pad contaminated with oil, grease etc. | Major |
| c. Brake lining or pad missing or incorrectly mounted | Dangerous |
Brake discs and drums
A brake disc or drum will only fail if it is significantly worn. Being worn below the manufacturer’s recommended limits isn’t a reason in itself.
| Defect | Category |
|---|---|
| a. Brake disc or drum: i. significantly and obviously worn | Major |
| ii. insecure, fractured or otherwise likely to fail | Dangerous |
| b. Contaminated with oil, grease etc. | Major |
| c. Missing | Dangerous |
| d. Brake drum back plate insecure | Major |
Brake performance check
The performance of the front and rear brakes and parking/emergency brake are checked for efficiency and balance using specialised ‘rolling road’ brake testing equipment.
Note: The brakes are checked both for efficiency of performance and their balance for equal braking side-to-side. For some vehicles the ‘rolling road’ brake test equipment cannot be used for technical reasons. In which case the Tester will drive the vehicle on the road using equipment to measure how effective the brakes are and whether they pull to one side of the other in operation.
The following categories apply to defects in this section:
| Defect | Category |
|---|---|
| a. Braking effort: i. inadequate at a wheel | Major |
| ii. not recording at a wheel | Dangerous |
| b. Brake imbalances across an axle such that: i. the braking effort from any wheel is less than 70% of the maximum effort recorded from the other wheel on the same axle. Or in the case of testing on the road, the vehicle deviates excessively from a straight line | Major |
| ii. the braking effort from any wheel is less than 50% of the maximum effort recorded from the other wheel on a steered axle | Dangerous |
| c. A brake on any wheel grabbing severely | Major |
| d. Abnormal lag in brake operation on a wheel | Major |
| e. Excessive fluctuation in brake effort through each wheel revolution | Major |
| f. Significant brake effort recorded with no brake applied indicating a binding brake | Major |
| g. Brake performance unable to be tested | Major |
Brake Efficiency
Calculating brake efficiency – roller brake tester
For most vehicles the MOT computer will calculate brake efficiencies automatically.
If the MOT computer isn’t working, the Tester will add the brake efforts from each wheel for the system that is being tested and carry out a calculation to determine brake efficiency.
The following categories apply to defects in this section:
| Defect | Category |
|---|---|
| a. Service brake efficiency: i. below minimum requirement | Major |
| ii. less than 50% of the required value | Dangerous |
Anti-lock braking system (ABS)
Any ABS systems fitted will be checked.
If the ABS has been intentionally rendered inoperative, the whole system must be removed. This doesn’t apply to sensor rings or other ABS components which are an integral part of another component, such as a brake disc or drive shaft.
It’s not permissible to remove or disable the ABS from a vehicle first used on or after 1 January 2010.
The following categories apply to defects in this section:
| Defect | Category |
|---|---|
| a. Warning device not working | Major |
| b. Working device shows system malfunction | Major |
| c. Wheel speed sensors missing or damaged | Major |
| d. Wiring damaged | Major |
| e. Other components missing or damaged | Major |
Electronic braking system (EBS)
The warning lamp operation on vehicles with an electronically controlled air braking system will be checked.
The following categories apply to defects in this section:
| Defect | Category |
|---|---|
| a. Warning device not working | Major |
| b. Warning device shows system malfunction | Major |
Brake fluid
Hydraulic brake fluid level checks are confined to transparent reservoirs, reservoir caps shouldn’t be removed.
A vehicle will be failed if it can be clearly seen that the brake fluid is contaminated.
The following categories apply to defects in this section:
| Defect | Category |
|---|---|
| a. Brake fluid contaminated | Major |
Link to all MOT Test procedures and failure items descriptions HERE