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Repair for MOT:
MOT Testing and Repairing BRAKESBrake Testing is an important part of the MOT Test – together with steering and suspension it is one of the longest sections in the Testers Manual. Testing a vehicle’s brakes may seem very straightforward but there are serious pitfalls for the unwary. Before going on to brake repairs we take a close look at the MOT examination of the vehicle’s braking system.
Whilst MOT Testing is essentially a commercial activity for most of us, with the possible exception of ‘designated authorities’, meaning organisations like police forces, ambulance maintenance organisations and local authorities who also do MOT Testing, we must never forget that the whole reason for the annual MOT Test is to ensure the public’s vehicles are safe to use on the road, so road safety is the keynote. In this respect Testing the vehicle’s brakes is perhaps one of the most important aspects of the MOT Test.
The problem faced by Testing Stations in road safety terms, however, is that the MOT Test does not allow for any dismantling of the vehicle systems, and an awful lot of the key braking components cannot be visually inspected. So from the customer’s point of view, as well as the road safety perspective it is very important that the brake Test is done properly.
Structure (including corrosion)
Throughout the Test of a vehicle’s braking system, there is the usual note in the Manual which states as a reason for rejection “Deliberate modification which significantly reduces the original strength, excessive corrosion, severe distortion, a fracture or an inadequate repair of a load bearing member or its supporting structure or panelling within 30 cms of... that is, within a ‘prescribed area’...”
This is a very wide definition, and you must make sure that supporting structure and panelling is also thoroughly inspected. Remember, they can ‘get you’ on corrosion for long after the vehicle has been Tested. The areas concerned are: “actuating linkage mounting point(s)... a parking brake mounting... the master cylinder/servo mounting.”
Four phases
Broadly speaking the MOT brake Test falls into four phases. Checks from inside the vehicle, underbonnet checks, examining the braking systems from beneath the vehicle, and Testing the brake performance. We will be looking very closely at each of these in turn.
Inside the vehicle
The pedal check
The brake Test starts as soon as the Tester first sits in the driver’s seat – what does the brake pedal feel like? Here is the first possible pitfall. Common sense suggests that the pedal should feel firm, and the Manual states a ‘reason for rejection’ as “sponginess indicating air in the system”, but be careful. It is all a matter of degree. Some vehicles notably Vauxhall diesels and the Nissan Bluebird as typical examples have a ‘softer’ pedal than might otherwise be expected, but that’s normal for these makes and models. Before deciding on a failure the Tester would be well advised to wait and see what result is revealed by the roller brake Test. The Nissan Bluebird for instance may have a ‘spongy’ but highly sensitive brake which engages very quickly on application. No problem, it’s all in line with the Manual because the ‘sponginess’ felt does not “indicate air in the system”.
Creep, however, is another matter. This indicates a problem somewhere in the system and should result in a failure.
At this stage any fouling of the pedal mechanism may be felt as a rubbing or vibration when the pedal is depressed. This in itself is not a reason for rejection. It will only fail if fouling causes “free movement to be obstructed”, so it can rub against something provided it doesn’t get caught up. But if it is rubbing, don’t forget to make a mental note to check it more thoroughly later and if it is OK list it as an advisory note.
Full story in MOT Workshop no. 12, November 05
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