Rotors within spec and not replaced.

I just took our car in for it's final checkup maintenance under the 4-year warrantee. They replaced the brake pads and sensors but did not replace the rotor because they were within specifications.

The rotor thickness currently is 22.8mm, the wear limit is 22.4mm, that's right we are .4mm away from the rotors being out of spec and needing replacement (Note: 0.4 millimeters = 0.0157480315 inches).

I am sure that within 3 weeks these rotors will no longer meet the BMW specs, does anyone know where BMW takes the measurements of the rotor and if within 600 miles or so we will use up 0.016" of rotor material (that's about the width of a hair on each side of the rotor)?

How many miles do you have on your car and did the computer say it was due for service? I have about 7K miles left before my warranty expires but the soonest service is for and oil change in 9K miles which I'll have to cover that out of pocket.

Originally Posted by richie1978

How many miles do you have on your car and did the computer say it was due for service? I have about 7K miles left before my warranty expires but the soonest service is for and oil change in 9K miles which I'll have to cover that out of pocket.

The brakes were squealing terribly, that is why they replaced the pads. I just want to double check their measurements just to be sure.
I am thinking about doing so serious mountain road driving this weekend just for the hell of it.

Go out and do some hard driving and braking!

Hi BLT, it's late and I don't have my spec book but you may be confused. Brake rotors have 3 specs. The first is nominal thickness which is what they were when they left the factory. The second is the minimum turning spec, ie, the minimum thickness that a shop can machine the rotors to. The third is the discard thickness, anything thinner than this and they are scrap metal.
Are you confusing the second and third? If they cut them slightly larger than the minimum machining spec than they have done you no harm and not 'cheated' you in any way.

The difference between minimum and maximum rotor thickness is usually 1.5mm-2.0mm or thereabouts. So I suppose they would argue your rotors are not quite 3/4 worn?

Originally Posted by DSXMachina

Hi BLT, it's late and I don't have my spec book but you may be confused. Brake rotors have 3 specs. The first is nominal thickness which is what they were when they left the factory. The second is the minimum turning spec, ie, the minimum thickness that a shop can machine the rotors to. The third is the discard thickness, anything thinner than this and they are scrap metal.
Are you confusing the second and third? If they cut them slightly larger than the minimum machining spec than they have done you no harm and not 'cheated' you in any way.

I am quoting the information on the invoice here is the quote in full.

"42942 road test and did hear a squeel noise under light application. It coming for the front wheel. I check and found that front brake is at 61/2mm and sensor is touching rotor. I found SIB#34-08-08. I perform that and found that it need front brake pads and sensor. Rotor measure at 22.8mm and min. 22.4 So I replace front brake pads and sensor only. Road test and the noise is gone."

Originally Posted by BLT

I just took our car in for it's final checkup maintenance under the 4-year warrantee. They replaced the brake pads and sensors but did not replace the rotor because they were within specifications.

The rotor thickness currently is 22.8mm, the wear limit is 22.4mm, that's right we are .4mm away from the rotors being out of spec and needing replacement (Note: 0.4 millimeters = 0.0157480315 inches).

I am sure that within 3 weeks these rotors will no longer meet the BMW specs, does anyone know where BMW takes the measurements of the rotor and if within 600 miles or so we will use up 0.016" of rotor material (that's about the width of a hair on each side of the rotor)?

Typically the thickness is measured at three points across the rotor to check for possible taper. Sixteen mils is only 8 mils per side and although that would not last until your (new) pads wear out it would get you thru the weekend. If indeed BMW cut them to within .4mm of discard then you have one hell of a complaint to lodge with the Service Mgr. My gut feel is that they cut them to within .4mm of the machining limit and that is industry acceptable and completely safe.

Originally Posted by DSXMachina

Typically the thickness is measured at three points across the rotor to check for possible taper. Sixteen mils is only 8 mils per side and although that would not last until your (new) pads wear out it would get you thru the weekend. If indeed BMW cut them to within .4mm of discard then you have one hell of a complaint to lodge with the Service Mgr. My gut feel is that they cut them to within .4mm of the machining limit and that is industry acceptable and completely safe.

They didn't turn the rotors at all, they just slapped on new brake pads and called it a day. There is quite a lip at the outer edge where the brake pads haven't worn away the rotor material. In fact if I draw my finger nail against the rotor I can feel the grooves and ridges left by the prior set of pads.

Originally Posted by BLT

I am quoting the information on the invoice here is the quote in full.

"42942 road test and did hear a squeel noise under light application. It coming for the front wheel. I check and found that front brake is at 61/2mm and sensor is touching rotor. I found SIB#34-08-08. I perform that and found that it need front brake pads and sensor. Rotor measure at 22.8mm and min. 22.4 So I replace front brake pads and sensor only. Road test and the noise is gone."

I will refer to my BMW specs in the morning and give you the facts. What the tech wrote can be interpreted in different ways. It is also odd, though not unheard of, that the pads would be changed without turning the rotors. Some mfrs. specify that the rotors ABSOLUTELY NOT be machined (turned) unless there is some sort of surface defect*. Normally worn/polished swept area is not considered a surface defect. I'll see what BMW says about that too.

* Here in New England you will find that 99.9% of all rotors have to be turned due to rust build up on the inner and outer edges which will often be rubbed by the new pads. Def makes a Rrrrrrrrrr noise when braking!

Originally Posted by DSXMachina

I will refer to my BMW specs in the morning and give you the facts. What the tech wrote can be interpreted in different ways. It is also odd, though not unheard of, that the pads would be changed without turning the rotors. Some mfrs. specify that the rotors ABSOLUTELY NOT be machined (turned) unless there is some sort of surface defect*. Normally worn/polished swept area is not considered a surface defect. I'll see what BMW says about that too.

* Here in New England you will find that 99.9% of all rotors have to be turned due to rust build up on the inner and outer edges which will often be rubbed by the new pads. Def makes a Rrrrrrrrrr noise when braking!

Thanks for all your help.

Originally Posted by BLT

They didn't turn the rotors at all, they just slapped on new brake pads and called it a day. There is quite a lip at the outer edge where the brake pads haven't worn away the rotor material. In fact if I draw my finger nail against the rotor I can feel the grooves and ridges left by the prior set of pads.

This alone does not neccessarily make it a bad job. After all, your old pads were able to properly stop the car using the same rotor surface. The new pads quickly wear to match this surface variation.
I'll see what BMW doctrine is on this in the morning. Stay tuned.

Originally Posted by richie1978

How many miles do you have on your car and did the computer say it was due for service? I have about 7K miles left before my warranty expires but the soonest service is for and oil change in 9K miles which I'll have to cover that out of pocket.

We currently have 42,328 miles on here and the computer say the brakes should be replaced at 43K.

Originally Posted by BLT

I just took our car in for it's final checkup maintenance under the 4-year warrantee. They replaced the brake pads and sensors but did not replace the rotor because they were within specifications.

The rotor thickness currently is 22.8mm, the wear limit is 22.4mm, that's right we are .4mm away from the rotors being out of spec and needing replacement (Note: 0.4 millimeters = 0.0157480315 inches).

I am sure that within 3 weeks these rotors will no longer meet the BMW specs, does anyone know where BMW takes the measurements of the rotor and if within 600 miles or so we will use up 0.016" of rotor material (that's about the width of a hair on each side of the rotor)?

This is where you use the customer survey to your advantage. Call the Service Manager. Point out the mere fraction of being out of spec your rotors are and tell him based on the decision his service department made you will not be able to give them passing scores on the survey.

Wow. That's BS.

I'd take it on a very long spirited mountain road drive and then to another dealership. Tell them that you measured them with several calipers and they are under spec. The other dealership's caliper needs calibrated.

Originally Posted by KrisL

Wow. That's BS.

I'd take it on a very long spirited mountain road drive and then to another dealership. Tell them that you measured them with several calipers and they are under spec. The other dealership's caliper needs calibrated.

Thanks, that's what I thought as well.

Originally Posted by KrisL

Wow. That's BS.

I'd take it on a very long spirited mountain road drive and then to another dealership. Tell them that you measured them with several calipers and they are under spec. The other dealership's caliper needs calibrated.

Excellent plan!!

Maybe get a good night's sleep and wait until DSXMachina returns with the specs?

I'm thinking that if they are indeed still 0.4mm off minimum thickness and the max-min difference is 1.6mm then it may take as far as 11,800 miles until you wear them out. I would think the amount of fuel used in order to do this might make it cheaper to replace the rotors yourself when the time comes.

most likely orig is 24mm with min being 22.4mm. like others have said, 25% remaining is still quite a bit left.

Originally Posted by BLT

We currently have 42,328 miles on here and the computer say the brakes should be replaced at 43K.

Do you mean the brakes should be replaced after 43K more miles or less than a 1K miles? Hmmm...so maybe the brake sensors actually work? I'm still confused on what they actually do, LOL

Originally Posted by jd325

Maybe get a good night's sleep and wait until DSXMachina returns with the specs?

I'm thinking that if they are indeed still 0.4mm off minimum thickness and the max-min difference is 1.6mm then it may take as far as 11,800 miles until you wear them out. I would think the amount of fuel used in order to do this might make it cheaper to replace the rotors yourself when the time comes.

I wanted to make sure I wasn't over reacting so I went to the garage and broke out the micrometer.

The thickness of a new two sided razor knife blade is .61mm, the thickness of a brand new single edge razor blade is .22mm. So I think it is safe to say we are talking about razor thin margins here.

What is the estimated cost of replacing the rotors?

Originally Posted by ralwhite

What is the estimated cost of replacing the rotors?

About $150-180 each axle for the parts, I am not sure what the labor cost are.

fixed prices for common service items up here. prices seem reasonable.

http://crm.bmw.ca/microsites/aftersa...P.aspx?lang=en

edit: also it's very unusual to only change the pads but not the rotors on a bmw. they're usually changed at the same time.

Originally Posted by BLT

We currently have 42,328 miles on here and the computer say the brakes should be replaced at 43K.

BLT,

Are you out of time on your maintenance plan? Sounds like your pads/sensor were replaced under warranty to fix the squealing, whereas the rotors couldn't be replace under warranty cause they were still within spec. And you are 700 miles too soon per the computer to have maintenance plan cover them.