Rear brake pads
 

I have two questions related my 2008 3.0si.



Situation: current mileage – 57,500. Front pad replaced at 43,668, rear pad replaced at 48,046


At 50,000 miles service indicator said – 37,000 miles left on front pads, 13,000 miles left on rear
At 57,500 service indicator says – 21,000 miles left on front pads, 3600 miles left on rear


My driving is mainly in city, stop and go, so I understand the quick drop. My questions are:
1. Why is rear dropping much faster than front?
2. In the inspection report last month (at 57,000) brake pads were measured at – Front: 11mm Rear: 9mm. Could service indicator be faulty?


thanks in advance.

The service indicator is a gimmick...at best it is a prediction/estimate.

Just measure the pads, go from there.

I haven't found the indicator to be gimmicky, but I do agree that the best approach is to measure the pads as you get closer. A dealer service advisor can do it in the drive-through bay, reaching in through the wheel, without lifting the car or taking a wheel off. I don't have that pad depth gauge, so I remove a wheel.

The reason the reading jumps is that there are two sensors in the E70 brake pad monitoring circuit, with two trip wires of different electrical resistances. The first is used to calibrate the algorithm to your actual wear rates. It is relatively early in the wear cycle, and adjusts the life-to-replacement indication. The second trip wire is used to say it is time to replace the pads. When the first trip wire is triggered, the life-to-replacement indication will jump (unless you were wearing pads exactly as per the preset algorithm)

When front pads wear faster (as is usual) it is due to them doing more of the braking. When rear pads wear faster it can be due to more frequent intervention of the traction control (braking a rear wheel in snow, for example) or a sticking caliper.

As you have a recent pad measurement, get them measured again and determine if you have a wear problem, or an indication problem.

So how does it tell you rotor condition?

:thumbup:

I wonder if maybe the two stage sensor was never 'reset' (replaced?) when he had the pads done last?

There is no way the OP has gone thru a set of rear pads in 9K miles unless the caliper with the sensor is dragging something fierce. I think we all know an E70 is fairly easy on rear pads, I agree with ard, it would seem to me that the dealer did the OP a solid and replaced the rear pads before the 4/50 ran out but didn't reset something or worse, failed to replace the sensor. :wow:

Get your pads checked OP. If you don't know a reputable indie shop now, find one.

Just get the pads checked.

Thanks everyone who responded.
I found the following articles / thread relevant and helpful:
http://www.xoutpost.com/bmw-sav-foru...ry-bypass.html
https://wiki.bentleypublishers.com/d...W+5+Series+E60
Brake pad sensor Question - BMW 3-Series (E90 E92) Forum - E90Post.com

I checked the brake pad thickness myself and got it checked at a local brake shop. Confirmed that I have 9-10mm of brake pads left.

Then I went to the dealer and asked SA - why does CBS show 3600 miles left, when I have 9mm of brake pads left. He thought my sensor is not set right. He called a technician to review and assess. Technician was confident that it’s not the pads or sensor, it is a computer calibration issue. He said that he can hook-up the computer and reset the sensor with existing pad condition of 9mm . I didn’t catch his full reasoning but I thought he mumbled that they might have forgotten to reset when they put new pads and sensor
at 48K.

First I didn’t believe him, as many people have said that resetting the CBS with half worn sensor will lead to “-----“ on brake miles. However he seemed very confident. SA agreed to do it for free, So I let them go at it.
He took the car in shop and did a special computer reset. Not the standard brake light reset. My car comes out of 18,000 miles remaining on Rear brakes. I am still intrigued what did he do but as long as it works I am happy.

Thanks again for help!