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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Technical Forums > Suspension | Brakes | Chassis > Break Pad Wear: How to know?



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      10-15-2012, 03:46 PM   #1
sle39lvr
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Break Pad Wear: How to know?

This might be a question that is asked frequently, but I couldn't find a solid answer.

My rear pads are worn out all the way. However, I am not getting a light on the dash. Do e90's get a light for worn-out break pads?

(I have owned several cars in the past, yet never waited till a light to change them)
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      10-15-2012, 04:36 PM   #2
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The sensors are on the front left and rear right wheels. sometimes, you may get uneven wear, or maybe your sensor is borked and isn't notifying you. If your pads are worn all the way, just replace them, don't wait for the service reminder.
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      10-16-2012, 09:35 PM   #3
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I'll give you a solid answer.

The brake system in your E90 has brake pad sensors in the left front and right rear brake. The sensors are dual stage, which means the sensors have two loops of wire in them. When the first wire is broken by rubbing on the rotor the CBS takes note of the mileage and estimates (assuming the way the car is driven doesn't change) and estimtes miles left on the pads. Once the senor second loop of wire breaks then the pads need to be replaced. Wait until the light to come on.
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      10-17-2012, 02:17 PM   #4
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just in case your sensors are malfunctioning... when u pull your pads out of the box and u look at the pad side, u will see the sides are shaved down at an angle. When a brake specialist looks at your pads, he will look for a groove between the pads an the rotor - these shaved down sides to the pad make that groove, when there is no more groove, your pads need to be replaced. Your rotors are similar... after so many pads have made contact with your rotor eventually a "bed" is seated in the rotor... if a "lip" on the outside edge of the rotor begins to exist, it may be time to change the rotor. in some cases, u can have your rotors "turned" and the lip is shaved off.. the bmw owners manual outlines minimum thickness for rotors for safe operation, if shaving off the lip makes the rotor less than minimum thickness, it is time to change your rotors.
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      10-17-2012, 07:29 PM   #5
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Thank you everyone.

Looks like I have to replace pads AND rotors soon.
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      10-18-2012, 07:43 AM   #6
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Quote:
Originally Posted by sle39lvr View Post
Thank you everyone.

Looks like I have to replace pads AND rotors soon.

What's your mileage on the rotors?
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      10-18-2012, 09:00 AM   #7
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Quote:
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What's your mileage on the rotors?
65K. I bought it at 40k ish CPO. Rear rotors have a huge lip and pads are all they way down..
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      10-19-2012, 04:09 AM   #8
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I'm in the same boat as you. Buying pads, rotors, and sensors for my car this afternoon.
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      10-19-2012, 10:14 AM   #9
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Quote:
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I'm in the same boat as you. Buying pads, rotors, and sensors for my car this afternoon.
Once done, care to share?
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      10-19-2012, 12:15 PM   #10
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Quote:
Originally Posted by sle39lvr View Post
Once done, care to share?
I just did all 4 corners on my 08 328i e93. It had 42k when I bought it. I'm pretty certain the rotors were original but the pads probably weren't because they were only half way worn. My reasons for replacement were twofolds. One, the rotors were deeply worn creating a ridge on the outside of the rotors. Secondly a grinding noise developed about 2 weeks after so I was hoping all new rotors and pads will eliminate the noise.

I ordered 4 slotted rotors from ecs tuning, akebono pads and sensors from rock auto. Turns out the rear rotors sent weren't for my car and did not fit. I was given a refund without have to ship them back. Another issue was the front new sensor not fitting snuggly into the akebono pads. It was the fault of the pads because the new sensor fit tightly with the old pads. This threw an amber BRAKE light on my dash and wouldn't let me reset the counter. I ended up cutting them, short the wires and taped it up. That cleared the light and allowed me to reset the counter.

I then had to get different slotted rotors from R1 concepts. They gave me a small discount for being a member here and allowed me to pick them up since I was local. The finish on them matched up well with the ones from ecs. Install went without any problems but it did not eliminate the grinding noise I keep hearing from the rear. Thinking it might be the parking brakes I went back and removed them completely. I'm currently driving with no parking brakes for a week now but the noise still exists so I'm pretty certain its a sticky caliper causing the pad to touch the rotor very slightly. I suspect its the passenger side one.

I'm probably just going to live with it cause it isn't causing uneven pad wear and also because of the hassle to bleed the system after replacing the caliper. Maybe when I can't stand it anymore I'll look into it again.
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      10-20-2012, 04:52 PM   #11
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do sensors have to be replaced each time you change the brakes or can they be reused?
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      11-02-2012, 01:25 PM   #12
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any play in the wheel while the car is in the air?

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