When it becomes necessary to replace Brake Pads, this presents an ideal opportunity to check on the condition of the Brake Discs. Firstly it will be apparent that the Brake Pads need replacing because of one of the following reasons:-
1. A warning light has appeared on the dashboard
2. Acoustic wear indicators can be heard when braking (if fitted)
3. The pads have been advised as low following a routine service or MOT test
4. The braking performance has deteriorated
When assessing the condition of the Brake discs. These are the things that should be checked :-
1. First check the Brake Discs have not reached the minimum specified thickness, this measurement should be taken from the centre of the friction area on one side to the same position on the opposite side, it is important not to measure from one unworn lip to the other, see Photo.
2. Do the brakes currently work perfectly well i.e. do they pull up in a straight line not pulling to one side or the other and without any undue noise.
3. Can any brake judder be felt when the brakes are applied?
4. A visual check of both sides of the friction surfaces should not reveal any deep scoring cracks or corrosion into the friction area. If one Disc seems OK but the one on the other side is not the pair must be renewed as this is the only way to get balanced braking plus the fact most suppliers will only sell pairs.
Having collected all the information needed to decide whether or not to replace the Brake Discs. Here are some further considerations:-
1. Brake Discs should last about two times the life of the Brake Pads, this varies from one car to another.
2. If the minimum thickness has not yet been reached the but the discs are within say 0.5mm of it. If Pads only are fitted by the time they have done a full term the discs will be considerably past the minimum.
3. If Discs need to be replaced independently later, the Brake Pads will again have to be replaced therefore doubling the cost of Pads and labour.
4. If scoring cracks or corrosion was found or any brake judder was experienced the Brake Discs should be changed to rectify these problems even if they were found to be over the minimum thickness.