The pad wear sensors are quite accurate as they wear down at the same rate as the pads.

Discs can be measures for thickness to determine if they need replacing but a visual inspection is usually enough. When the lip on the outer edge is very visible then they need changed

The squeaking you can hear is probably lack of copperslip compound on the rear face, not the friction pad, of the brake pads, common fault.

Sounds as if your cars brakes need a good service.

 

Pads and Discs are extremely expensive

Are they?

When a tank of fuel lasts less than a week and discs/pads last one, two or even three years; I would say they are relatively inexpensive.

Given that the computer should tell you when a pad or disc requires replacing, .

Never trust computers!

Mind you, the breaks / alloys / discs or something is squeaking rather annoyingly, but that's been the case since a year or so ago?

:? Maybe someone should have a look on your behalf to determine what the noise is . It may be something serious/dangerous

Is there a theory that it's 2 sets of pads for once set of discs? And how long are discs supposed to last then? Confused...

No.

If your discs are made of chocolate and your pads concrete then the reverse would be true.

You really nee to get someone who knows what they are looking at to have a nose for you.

 

I hesitate to suggest that one could remove a wheel, eyeball the pads, and measure the disks with a micrometer or vernier. I know it could take 5 minutes, but ...

 

The pad wear sensors are quite accurate as they wear down at the same rate as the pads.

Not so, they do not wear with the pads. That is why people replace pads but try to keep the same sensors, they are not worn. For some reason the car likes a new set of sensors or you cannot reset the OBC. However I still think disconnecting the sensor may allow reset as they are very basic and no compex electrics in them. I reckon just the disconnection may do it.

If you get a warning light about pads then the sensor will have triggered it in the main.
The OBC must measure your breaking and speed etc, that is how you get the countdown, it cannot be the sensor as it does not touch the disc for ages, that just has the final say.

 

I would agree that the sensors cannot be trusted, the OBC states my rear pads need doing in 16000 miles but I had my brakes in bits last week to clean them I can defo say that i'll be lucky if they last another 6000miles.

 

Not so, they do not wear with the pads. That is why people replace pads but try to keep the same sensors, they are not worn. For some reason the car likes a new set of sensors or you cannot reset the OBC. However I still think disconnecting the sensor may allow reset as they are very basic and no compex electrics in them. I reckon just the disconnection may do it.

If you get a warning light about pads then the sensor will have triggered it in the main.
The OBC must measure your breaking and speed etc, that is how you get the countdown, it cannot be the sensor as it does not touch the disc for ages, that just has the final say.

I changed my pads and sensors today (using the very good guide from the 'How to' section), about 3-4 months and approx. 5,000 after the sensors originally highlighted that they needed to be done. There was still a bit of wear left in the pads but I thought it best to change them rather than leave it too late.

I may be completely wrong here but the sensors seem to be plastic coated and as the pads wear down, the plastic tip wears, finally revealing a metal connector that, I think, connects with the disc, forming a circuit and flagging the wear to the OBC.

I think the sensors flag up excessive wear WAY to early but I am sure that this is a ploy by BMW to get most people to change their pads more frequently!

 

Sensor mileage react to the rate of wear. I had like 30k miles left in the rears, did a trackday, and they went down to 7k something. Have driven approx. 10k miles since then, and now they are showing 11k miles! Still original pads from new, 52k miles in! They will last forever it seems... don't brake much, and when I do, it's hard so it's mostly the fronts that take a beating...

 

From watching alot of YouTube videos the brake wear mileage can go into minus figures!

From what I can tell the actual sensor does not become activated until it is worn right down by the disc and if you replace pads in time you can reuse. So until the sensor is activated its just an approximation which is probably calculated in some strange way!

 

From watching alot of YouTube videos the brake wear mileage can go into minus figures!

My brake wear mileage was showing up as -400,000 when BMW had a look!They blamed the reading on the previous owner using non-BMW parts however when I changed the pads at the weekend they were exactly the same as the OEM ones I was replacing them with!

From what I can tell the actual sensor does not become activated until it is worn right down by the disc and if you replace pads in time you can reuse. So until the sensor is activated its just an approximation which is probably calculated in some strange way!

From what I saw on mine yesterday, this is how I think it works. I guess the only issue with reusing the sensors is that anything could get stuck between the disc and the sensor (water for example), completing the circuit and flagging up excess wear to the OBC. By fitting a new sensor which has the connector pastic coated, it is not going to complete the circuit until the tip has worn down.

 

I changed my pads and sensors today (using the very good guide from the 'How to' section), about 3-4 months and approx. 5,000 after the sensors originally highlighted that they needed to be done. There was still a bit of wear left in the pads but I thought it best to change them rather than leave it too late.

I may be completely wrong here but the sensors seem to be plastic coated and as the pads wear down, the plastic tip wears, finally revealing a metal connector that, I think, connects with the disc, forming a circuit and flagging the wear to the OBC.

No, you are not wrong. They merely work like any other sensor. That is why they can tell you nothing until the wire is reached. Plus they do not touch the disc until a certain thickness of pad is achieved.

 

Just check them yourself it's not hard to jack it up and take a wheel off, if you got big 208mk you should be able to see without having to take the wheel off anyway!