[vladman]

Just had the car MOT-ed, it passed, not even an advisory.

New discs arrived in the post, so now they're ready for installation when needed.

The car can't warn you when the discs are "too worn", right? Only for pads? Would someone mind explaining how the sensor works? Do we basically ignore the (woefully inaccurate and pretty much useless, at least in my own experience) iDrive, and wait for the warning to come up on the dash?

Many thanks!

[suj999]

Idrive is based on driving based calculations.

Brake pad light is contact based and will kill the sensor once activated. Meaning will need to replace the sensor once activated. It's set to activate once the pads wear to nothing.

[warmshed]

Pad sensors are fitted to the metal backing of the pads, they extend into the pad area so that when the pad has reached its minimum thickness the disc rubs the sensor and shorts out sending a signal to the cars warning system.

On many cars the sensor can be reused on new pads, being away from the disc prevents them shorting out, but its a suck and see situation, you can always test before putting the wheel back on and it only takes a few seconds to change to new ones if there is a problem. I have reused on previous cars without any problem. Some sensors just fit in by friction or springs, some cars they are actually part of the pad.

http://www.pelicanparts.com/BMW/tech..._Pads/pic3.jpg

[Im1]

Originally Posted by spirocheter

I have had terrible issues with non genuine BMW brakes. I am still running my 2008 335d, which I had under extended warranty. The price I was quoted by BMW for replacement of discs and pads (I can't remember the figure) seemed excessive and I opted to buy from Eurocarparts, the most expensive Pagid discs, and Pagid pads (front and rear). I bought sensors for brake pad wear from EBay.

I had a local trusted mechanic fit them and within only 2k miles, and gentle driving (I'd driven my previous car far far harder), not applying brakes etc when warm, they had warped, not by a huge amount, but the juddering was very noticeable even from speeds of around 50 with light braking. I was told by my mechanic, the manufacture of Pagid had been moved to China and the carbon content of the steel was of much poorer quality.

I tried to get Brembo, but my mechanic was having difficulty obtaining them, and he recommended Honeywell discs and Bosch pads (in stock with his supplier), so I went with these. Again, exactly the same problem, not quite as severe. He assured me there were no other mechanical issues. Another set of warped brakes. Not as severe as before, but still too bad to live with with wear on suspension components etc.

I then took my car to a BMW specialist, who is very highly regarded. I asked him to check the hub faces were not out of alignment etc and he checked everything very carefully. He advised Bosch discs and Bosch pads, sounded OK to me, all German (just changed the front discs). Now these have been the best yet, but if braking quite firmly from, let's say 70mph, there is still a very slight judder. I should say I've not changed the rear brakes since switching to the Pagid. It is acceptable now but slightly annoying at times.

The whole experience took me close to selling the car. I will never spec any brakes other than genuine again. I notice there is an EBay seller presently in Germany selling genuine BMW brakes (I was looking this up before buying my F11, which I'm due to collect tomorrow)!

Yes, they are more expensive, but will potentially save enormous hassle and significant performance issues. I should mention, I had a local garage replace my e46 330d brakes years back, not even thinking about the potential issue of problems, and they squealed like pigs. I traded the car because of this! This is why I had extensively, I thought, researched the issue of which discs and pads to go with on forums etc before I bought for the 335d!

Buy genuine!

Exactly this . Don't contaminate with non OEM brakes , similar escapades for me when I tried to save a few quid on new discs on 2 previous cars

[mobilejo]

Originally Posted by Im1

Exactly this . Don't contaminate with non OEM brakes , similar escapades for me when I tried to save a few quid on new discs on 2 previous cars

Me too, on too many BMW's to list. Squeal, squeak, judder - had pads/discs from Pagid, Jurid, Brembo supplied by ECP, GSF, Indy, fitted DIY, fitted by Indy - too many different silly little niggles to mention over the years.

This time when my 535d needed front brakes, I just paid full whack and let BMW do it. It's their problem if any issues arise (first plus point) but the issues are less likely to arise as the parts are all original (second plus point).

[Fox530]

Originally Posted by vladman

Just had the car MOT-ed, it passed, not even an advisory.

New discs arrived in the post, so now they're ready for installation when needed.

The car can't warn you when the discs are "too worn", right? Only for pads? Would someone mind explaining how the sensor works? Do we basically ignore the (woefully inaccurate and pretty much useless, at least in my own experience) iDrive, and wait for the warning to come up on the dash?

Many thanks!

My understanding of how the sensor works (This has been notoriously difficult to figure out, almost nobody seems to know even the dealers, so I could still be wrong):

From new, the car counts down the pad life using a specific algorithm. I don't know whether this is linear, whether it uses fuel consumption to estimate driving style, or whatever. But it counts down.

Once it reaches 2200 miles (Which is 3500km) it stops counting down and sits on 2200 miles without changing. It will sit here until the first stage wear sensor is triggered. It then resumes counting down, using the time taken from new to first sensor to calculate a more accurate remainder.

At some point, it'll trigger the second stage wear sensor which pings up the brake pad light on the dash.

Now of course I cannot 100% state that the above is true, however on my last F10 the rear pads stayed at 2200 for about 4000 miles and then continued counting down. I checked them at 1000 miles to go and they were ready to change. We also have a Mini Cooper - it too has been sitting on 2200 miles to go for months and months now and there is plenty of life left so it's presumably waiting for the first sensor before resuming countdown.

Hope this is of use!

FWIW I got to 45k on my rear pads and had to replace my front pads at 50k because despite having plenty of life left they'd begun to rust to the caliper due to age (Car was at that point over 6 years old on its original pads!). My current F10 is on 8k miles and reckons I've only got 19k left front and back! I'd be somewhat irritated if that turns out to be true...

[vladman]

Hi Fox, thanks for your detailed response.

My experience with iDrive has been different, or rather, like yours, it seems to reach a certain number and then stop there for ages, before it continues again. So I don't think 2200 is a "magic number". For example, my front brake pads stopped at 10000 and didn't budge for months and months, and then suddenly dropped to 1600. Now they're stopped at 1600 again. Different numbers again with rears.

All in all, in my experience at least, these numbers are nearly useless. I mentioned in another thread, that when I picked up my car from the dealer, when I bought it (approved used), it was showing 130000 (yes, one hundred and thirty thousand) for the front pads? And that number wasn't changing either, for months as I drove the car, until I mentioned it to another dealer, when the car was in for its regular service, and they returned the car to me with that number down to 19000 (how or why they picked 19000 is beyond me). They didn't explain it to me either when I asked.

[Fox530]

Interesting, I assumed 2200 was the 'magic number' as both our cars stopped there and only there - it seemed an odd number until I realised it was 3500km.

I suppose the reality is that everyone wears brakes differently and the physical pads themselves are not high tech or fitted with expensive reporting sensors, so it's a 'best effort' guess using a bunch of estimated parameters.

130000 seems mad - when mine was reset after new pads it displayed approximately 45-50k to go.

Which makes 18k left on my 8k mile car all the more odd really!