[jvrb]

How accurate are the brake pad sensors?

I had my F25 X3 2.0d in for a general service about a month ago.
Before the service I checked how many km's were left on the front and rear pads on the Vehicle Status screen. Rear brakes had been done not long ago, they were 36,000km.
The front brakes said 13,000km left.
When I picked up the car after the service I was told that the front brake pads and rotors would need to be replaced in 3,000km. When I mentioned the 13,000km before the service it was more or less waved off.
When I drove away from the dealer and checked the status again, surprise, surprise, it said that the front brakes had 3,000km left.

Now I get a service message and it says the front brakes need to be serviced in 1,000km.

So I checked them (only one side).
Front pads have around 4.50mm left.
Rotor is 27.4mm, minimum is 26.4mm.

I reckon I can do more than 1,000km with the above pads and rotor.
Or should I just get them changed.
I know it will cost me over AU $1,000 to do.

Thanks for any advice.

[Tjalle]

I would not rely on message, but check also other side - it is safe to go down to 2mm for pads.

Normally you don't have to change discs every time you install new pads. Pads will adapt to worn discs - within reason. The important thing is that brakes can activate ABS.

This is obviously a major moneymaker for BMW and dealers.

I will change brake fluid every four years - not every two.

[BMWrules7]

Originally Posted by Tjalle

I would not rely on message, but check also other side - it is safe to go down to 2mm for pads.

Normally you don't have to change discs every time you install new pads. Pads will adapt to worn discs - within reason. The important thing is that brakes can activate ABS.

This is obviously a major moneymaker for BMW and dealers.

I will change brake fluid every four years - not every two.

The CBC, condition based service, is notoriously unreliable for computing the brake pad interval.

The reason your computer made a downward adjustment was due to the tech entering in the current values into the system as opposed to the system's estimated value. The estimates were wrong.

Now, there is a final wear sensor that is extremely accurate. This has nothing to do with the CBC computer estimating wear. The final wear sensor is an actual alert once the brake wear exceeds the minimum threshold. If the final wear sensor trips, your car will alert you that it's now time to change the pads.

In general, BMW does not try to screw the customer with its CBC computer. In many countries, the CBC systems are used to kick off $0 maintenance that it's not to BMWs advantage to screw the customer with CBC since in many cases BMW is paying for the pads under maintenance.

[Polo08816]

Originally Posted by Tjalle

I would not rely on message, but check also other side - it is safe to go down to 2mm for pads.

Normally you don't have to change discs every time you install new pads. Pads will adapt to worn discs - within reason. The important thing is that brakes can activate ABS.

This is obviously a major moneymaker for BMW and dealers.

I will change brake fluid every four years - not every two.

4 years is a long time to go on brake fluid.

[Tjalle]

Polo,no it's not.

I have been forced to change one brake cylinder after 11 years, because of corrosion- SAAB 9000.

There are millions of cars not having changed brake fluid ever -including ABS equipped cars - which is not what I would recommend.

[Polo08816]

Originally Posted by Tjalle

Polo,no it's not.

I have been forced to change one brake cylinder after 11 years, because of corrosion- SAAB 9000.

There are millions of cars not having changed brake fluid ever -including ABS equipped cars - which is not what I would recommend.

It is.

There are a lot of HPDEs that won't even let you on a track if you haven't had your brakes bled in the past 6 months or year.

I've worked on cars that have gone for years (4+) without having the brake system bled. It's not uncommon to have some bleeder valves that are seized due to corrosion.

I also believe BMW recommends brake fluid changes every 2 years as well.

[Tjalle]

I believe BMW recommend change after 3 years and then every two years. My fluid was not changed at my free two year service.

Brakefluid is hygroscopic - it will - in time - absorb humidity from the air, which turn into water at - primarily - brake cylinders. Theoretically also in ABS system.

Worst case scenarios are pushing a STD car at a track or - even worse - do a "Tourist run" down a special 20 km downhill road in the Alps, where all European car manufacturers are testing for brake failure - water in fluid starting to boil=loss of brakes.

Those who will not go down that moutain nor driving on a track, just have to beware of brakecylinder corroding=loss of braking power on that particular wheel.

I have worked for a car manufacturer - we had no brakefailures with 4 years old fluids.

A stuck bleeder valve is no danger - just an issue.

[jvrb]

Thanks for the info.

I gathered that the sensor would be more accurate and would send a signal once the pads had reached a certain thickness. The 4.5mm matches some of the figures I found when doing a search online.
I'll keep checking the pads on both sides and not get too worried at having them replaced exactly within the next 1000km.
As for the rotors, there is 1mm left before they reach minimum thickness.

Once the car is out of warranty I will probably do the brakes myself.
I do them on my 4WD ute (utility, or pick-up for the uninitiated) without too much hassle. On the ute I have to repack (or replace) the wheel bearings when doing the front rotors.

[Tjalle]

Beware, typically pads do not reach the outer part of disc - i.e. there is a ring of non-worn disc, that you will measure.

Again - if brakes have enough power to activate ABS on tarmac, you are OK.

[Northandy]

Recently had the same with mine, countdown was at 10k miles for the rears then dropped to 2k in one day, then gradually dropped lower each day.

My understanding is that the car estimates based on driving, but then the sensor triggers at 2km left.

I had mine checked and rear pads were needed, visually you could see through the wheel there was little pad material left too (2mm) car has covered 28k so far

[Tjalle]

I live on the west coast of Sweden, and today we had a rare situation with sun and no wind. Consequently I washed my car and checked tyres, discs and pads.

16800 km of which about 15000 on summertyres.

Pads are down to 10mm front and 9mm rear - 11 resp 10 at BMW service at 15.000 km

Discs are worn about 0.5 mm on each side - will last "for ever"

Tyres (summer) are down to - new 9 mm - 6mm front and 5mm rear.

I don't understand more wear at the rear - anyone?

20". 245/40 front, 275/35 rear. As specified, 2.2 bar.
.

[poiuytre111]

The F25 is biased in its use of brakes towards the rear to keep the car level when braking. I suspect the 4wd is also biassed to the rear which might mean more rear wheel rubber left on the road whether accelerating or braking.

[jvrb]

Originally Posted by Tjalle

Beware, typically pads do not reach the outer part of disc - i.e. there is a ring of non-worn disc, that you will measure.

Yes, which is why I use a micrometer to measure the rotor thickness.



My rear pads were worn before the front ones as well. Tyres all seamed to wear at a similar rate.

[Tjalle]

Micrometers are good .

Yes, I can buy that brakes are biased towards rear - even on F26 . To 99%, I brake very gently, but it might still have a, very small, impact on tyre wear.

Yes, obviously AWD IS biased towards rear. That is likely the reason for somewhat more wear at rear. My right foot is a bit more heavy on the throttle, than brakes.

I expected more wear upfront due to heavy engine, but biased AWD is most likely the explanation.

Thanks.

[Polo08816]

Originally Posted by Tjalle

I live on the west coast of Sweden, and today we had a rare situation with sun and no wind. Consequently I washed my car and checked tyres, discs and pads.

16800 km of which about 15000 on summertyres.

Pads are down to 10mm front and 9mm rear - 11 resp 10 at BMW service at 15.000 km

Discs are worn about 0.5 mm on each side - will last "for ever"

Tyres (summer) are down to - new 9 mm - 6mm front and 5mm rear.

I don't understand more wear at the rear - anyone?

20". 245/40 front, 275/35 rear. As specified, 2.2 bar.
.

Originally Posted by poiuytre111

The F25 is biased in its use of brakes towards the rear to keep the car level when braking. I suspect the 4wd is also biassed to the rear which might mean more rear wheel rubber left on the road whether accelerating or braking.

Originally Posted by Tjalle

Micrometers are good .

Yes, I can buy that brakes are biased towards rear - even on F26 . To 99%, I brake very gently, but it might still have a, very small, impact on tyre wear.

Yes, obviously AWD IS biased towards rear. That is likely the reason for somewhat more wear at rear. My right foot is a bit more heavy on the throttle, than brakes.

I expected more wear upfront due to heavy engine, but biased AWD is most likely the explanation.

Thanks.

There's more wear at the rear for many reasons:
- The weight distribution is more even between the front and rear axles than a 335/340i
- The X3 has a higher towing capacity than the typical sedan so there's slightly greater brake bias at the rear axle

How the AWD system is biased doesn't have that much to do with why the rear brake pads are wearing faster.