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Hive mind:

We recently took the X for routine scheduled maintenance to do front brakes. I assumed this was as it has been in the past for pads alone, rotors if needed. I was told "Oh no no no sir, BMW always recommends rotors be done with pads." I bent at the time, but now I wonder. We're about to go back for rear pads, and I wonder... could this be true? There are no symptoms of bad rotors.

I ask because it was later discovered the SA came close to having me spend unnecessary money on a diesel particulate sensor that should have been covered under warranty.... I trust no one now. Thanks in advance.
 

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This is based on measurement of remaining rotor life, so need to be certain mm width otherwise they will recommend changing them.
 

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The rotors used to/maybe still have a minimum thickness stamped on them. But, it's standard practice to replace the rotors instead of turning (machining) them. A thinner rotor will get hotter under heavy breaking, and it will be more likely to warp.

Years ago, the car manufactures decided to save weight by making the rotors as thin as possible. So, it's not just BMW dealers that tend to always replace the rotors when replacing the pads.
 

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02/2012 X5 35d M57Y CPO 99K miles NOKIAN WR G3 12K miles
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As predicted, they tried to upsell rotors again. "What is the thickness remaining?" "I dunno, I'll ask the tech... brb." "He says 29mm, lower limit is 23. " "Then this would be more, then, wouldn't it?" "They may squeak." "yeah, I'm good with pads only thanks."

MainLine BMW.... I see you. :mad:
 

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As predicted, they tried to upsell rotors again. "What is the thickness remaining?" "I dunno, I'll ask the tech... brb." "He says 29mm, lower limit is 23. " "Then this would be more, then, wouldn't it?" "They may squeak." "yeah, I'm good with pads only thanks."

MainLine BMW.... I see you. :mad:

Actually, they were pretty honest to tell you what the minimum thickness is and just change the pads. Most dealers, and a lot of indy's, just say it's not done.

It's standard and good practice to have the rotors machined ("turned") when replacing the brake pads. Brake rotors will warp, and that warping comes out of the 6mm you have left. The valleys of the warp have to be cut down on both sides of the rotor. Also, brake rotors "knife" when they wear, meaning that they wear down more near the out edge than near the hub. The outer edge is also where warping (technically called "axial run-out") is also the most severe. So, that also cuts into the 6mm of spare metal you still have on your rotors.
 

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Actually, they were pretty honest to tell you what the minimum thickness is and just change the pads. Most dealers, and a lot of indy's, just say it's not done.

It's standard and good practice to have the rotors machined ("turned") when replacing the brake pads. Brake rotors will warp, and that warping comes out of the 6mm you have left. The valleys of the warp have to be cut down on both sides of the rotor. Also, brake rotors "knife" when they wear, meaning that they wear down more near the out edge than near the hub. The outer edge is also where warping (technically called "axial run-out") is also the most severe. So, that also cuts into the 6mm of spare metal you still have on your rotors.
6mm is a ton of meat left on the rotor. 5mm is approx 1/4 inch = 0.250 inches. When I did track events at the instructor level (retired club racer) using race pads, I'd wear about 0.001 inches of the rotor per weekend (Laguna Seca ate twice that, but it's super hard on brakes). So I could do >250 track weekends with 0.250 inches of rotor left. Plenty for a second set of pads on a street driven vehicle imho. If you're towing a super heavy trailer in the mountains I'd err on the side of caution, but there's no reason for mortals to change their rotors with that much meat left on them.
 

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Follow up question: Will the brake warning on the instrument cluster and control display automatically reset if I put on new pads (and possibly rotors)?
 

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Follow up question: Will the brake warning on the instrument cluster and control display automatically reset if I put on new pads (and possibly rotors)?
@BrianZHP....I will assume you are talking about the Brake Pad warning symbol. You will need to also replace the Sensors if they are worn thru, which usually triggers the wear warning light. One of the driver side front & passenger side rear.
Check these videos out for resetting the warning lights. The video shows resetting the oil & brake fluid change. Just scroll to the front or rear brakes with the dash button
Hope this answers your question


https://youtu.be/fAsErymaiio

https://youtu.be/b26t8TSfHDs
 

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Thank you for the info @rav31. I'm going to be doing the brakes shortly and have a follow up question before I order parts... The brake pad warning light did not come on randomly while driving. The "service due in xxxx miles" counted down to zero and that's when the warning came up. So on my dash, I have the little exclamation point warning symbol on the left side PLUS the "BRAKE" light on the right side, plus the warning on the control display saying that pads are due. (Passengers keep thinking my parking brake is on.)

So my question is whether or not the pad sensors are seeing a thin pad lining or if the service interval triggered the warning or both. Or do the pad sensors start the service interval countdown and tell the vehicle that a typical driver has XXXX miles left on the pads?

I'm used to working on my e46, so I'm not up to speed on this one yet.

Thanks again!
 

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Thank you for the info @rav31. I'm going to be doing the brakes shortly and have a follow up question before I order parts... The brake pad warning light did not come on randomly while driving. The "service due in xxxx miles" counted down to zero and that's when the warning came up. So on my dash, I have the little exclamation point warning symbol on the left side PLUS the "BRAKE" light on the right side, plus the warning on the control display saying that pads are due. (Passengers keep thinking my parking brake is on.)

So my question is whether or not the pad sensors are seeing a thin pad lining or if the service interval triggered the warning or both. Or do the pad sensors start the service interval countdown and tell the vehicle that a typical driver has XXXX miles left on the pads?

I'm used to working on my e46, so I'm not up to speed on this one yet.

Thanks again!
@BrianZHP.........As far as the brake sensor is concerned, it's just like your E46. Once the pads get down to a certain thickness, (that's inside pad on LF & RR) which I think is approx. 3/32", 2.4mm, .093", the plastic sensor wears away until the internal wire is worn through, allowing for an open circuit and then displaying a "warning" on the dash. To be honest, IMO, you have plenty of brake pad left at that time to drive for several thousand miles of normal driving. Some new owners to BMW panic when they see that & stop where they are.
Best thing you can do is remove wheel & check pad thickness & rotor thickness, to see where they are. BMW service centers have a "Min" thickness. see here on TIS

When we bought our CPO '15 F15 several months ago, the dash warning would display "service brakes in 3200 miles". Unfortunately, this is only a reminder that the BMW dealer put in & does not "count down". I just use a flash light & look at the pad thickness from out side the wheel to see how it's doing. In my opinion, your just wasting your $$ by replacing early. I'd need to see a picture of what your dash warnings are to try & figure if you have something else going on or not.
 

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I got the same "service brakes in 3200 miles" text message a month or two ago on the screen. They looked/measured it during the recent routine maintenance and said it's all just fine/thick.
 

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Good intell. We just started getting the 3200 mile service indication. Will pull wheels next oil change and check. Will do it at CCA event so hopefully shop will have tool for testing rotor.

For when they are needed, what pads are owners using?
 
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