11-09-2013, 08:03 AM | #1 |
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Replaced brake pads
Our 116iM has been driven quite a bit on race tracks, so the brake pads were ready for replacement up front at around 24000 km. At the back, more than 50 percent pad material is still left.
The iDrive says I have 2 200 km left in the rear, and 120 000 (!) km up front, so the car really doesn't have a clue. It was rather easy to swap the pads. On my previous BMWs I have used a 7 mm allen bit, but BMW have changed this to 8mm. Luckily my 8 mm allen key was enough to do the job. I didn't need the ratchet. It was possible to take the caliper spring on and off with just my fingers, and I could also push back the piston without tools, so the whole job was done very quickly. If I had larger wheels (18"), I think I could have done it with the car standing on the wheels. After I reset the service counter for the front brakes, it still said 120 000 km left. My dealer said it was abolutely necessary to replace the brake pad sensor, but I doubt this advice, so I just swapped over the old one to the new pad. |
11-09-2013, 03:05 PM | #2 |
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I have heard from several sources that the sensors should indeed be replaced with the pads. The fact that the service prediction hasn't changed would suggest the sensors have failed already.
But if you are comfortable enough to know what you can expect from the pads anyway as I suspect you are then maybe the sensors can be ignored quite easily.
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11-09-2013, 03:10 PM | #3 | |
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11-09-2013, 03:22 PM | #4 | |
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11-09-2013, 03:52 PM | #5 |
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The pad sensor is a piece of plastic with a metal strip in it. All it can do, is measure a short circuit (to the brake disc) or a broken strip (by the brake disc). For this to happen, the pad must be worn down almost to the back plate. As long as the plastic housing is not damaged, I think it is safe to reuse it. But I don't know for sure.
In some previous cars, I have replaced the pad sensors with a short circuit link directly in the connector, just to avoid warning lights. |
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11-09-2013, 04:59 PM | #6 |
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I did actually google how these brake pad sensors work, and found a lot of unreliable information. A lot of people seem to think the sensors have two circuits, are magnetic and other strange ideas. I think all that is wrong.
If you take a look at the connector, it has only two pins in a plastic housing. That means is has ONE circuit. The resistance between the two pins is 0.3 ohm, which is pretty much a short circuit. The sensor does not stick to metal, so it is not magnetic. Two things can happen to it as the disc starts grinding down the plastic. 1) The circuit can be grounded to the disc. 2) The circuit can be broken. If it was an analog proximity sensor of some sort, it would have been more expensive, and would have more pins in the connector. Since the sensor is buried rather deep into the brake pad, there will be no damage to it at all until the material is almost gone. At this point, the pads should definitely be replaced. Before this happens, the car can only guess based on you driving pattern how much pad life there is left, and it does a very bad job at this, at least with my driving style. |
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11-10-2013, 03:56 AM | #7 |
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Seems we can deduce a top tip from your investigations then :-
If BMW says the pads need changing, have a look before putting your hand in your pocket.
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11-10-2013, 12:42 PM | #8 | |
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I think you are correct in saying that the sensor detects either a short circuit or a broken cirquit. This happens when the pads are worn enough to start waring out the sensor. As I recall, there was still sufficient brake pad material left after the sensor had triggered the alarm, at least for a couple of 1000 kms normal driving. So I would never replace brake pads earlier, but ofcourse you should know better according to your own driving style. All in all, I think the sensors are a good way to know when to replace brakepads. As for the Idrive status of your brake pads, its probably indeed just an estimate based on your mileage and driving style. It goes down gradually on my car, so maybe something isn't 100% working if yours keeps saying 120000km.. By the way, how often do you replace brake disks? Every second time you replace the pads? (Disks should always be replaced together with new pads!) Last edited by Math; 11-10-2013 at 12:48 PM.. |
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11-10-2013, 03:49 PM | #9 | |
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I don't know yet for the F20, but on earlier cars I have had 2-3 sets of pads per disc. |
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11-11-2013, 06:14 AM | #10 | ||
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The example given is: Quote:
The simple single stage wear sensors are only able to give a worn-out signal. Both single and dual stage wear sensors need replacing at pad change, if you want 100% communication to the ECU. HighlandPete |
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11-11-2013, 09:28 AM | #11 | |
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The service indicator counts down before the sensor is triggered, so it must be based on how hard and frequently we are braking. |
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11-11-2013, 10:40 AM | #12 | |
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I know for my car the rear pad rate is now reversing, I've gained 2k miles in the last 5k miles, gone up from 14k to 16k miles. I'll be maeasuring my pad thickness when I swap over to winter wheels in the next few days. I wonder if my rear pads have now worn to the first break in the sensor circuit and it has recalculated the mileage. So you are changing pads well before the first contact with the brake disc. What have you got left, over 6mm pad thickness? HighlandPete |
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11-11-2013, 10:49 AM | #13 |
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I would estimate that my front pads were about 70 percent worn down, and the sensor was still not touched (getting close, though). Maybe 3-4 mm left of the pads. I didn't actually measure them, so take my figures with a grain of salt.
The sensor sits very deep. A part of it is actually on the other side of the back plate. |
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