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At over 99,000 miles, while the car was in for an oil service, I had my tech check the original brakes.

I forgot to ask him about the brakes after the service but, he indicated on the bill that the fronts were at 6mm and the rears were 7mm and apparently not in need of replacement.

What does that mean and at what mm is a change necessary?

Thanks.
 

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Re: Please answer a brake question for me....

Tranck,

If they are in fact the original brake pads you're past the point of " how much farther can I go". Through so many heat cycles your pads could be hard and cracked. If it were my car I'd be replacing the pads and rotors for the next 100K. You would notice a difference in stoping distance.

BWM recommend pads replacement at 3mm. <!--[if gte vml 1]><v:shapetype id="_x0000_t75" coordsize="21600,21600" o:spt="75" o:preferrelative="t" path="[email protected]@[email protected]@[email protected]@[email protected]@5xe" filled="f" stroked="f"> <v:stroke joinstyle="miter"/> <v:formulas> <v:f eqn="if lineDrawn pixelLineWidth 0"/> <v:f eqn="sum @0 1 0"/> <v:f eqn="sum 0 0 @1"/> <v:f eqn="prod @2 1 2"/> <v:f eqn="prod @3 21600 pixelWidth"/> <v:f eqn="prod @3 21600 pixelHeight"/> <v:f eqn="sum @0 0 1"/> <v:f eqn="prod @6 1 2"/> <v:f eqn="prod @7 21600 pixelWidth"/> <v:f eqn="sum @8 21600 0"/> <v:f eqn="prod @7 21600 pixelHeight"/> <v:f eqn="sum @10 21600 0"/> </v:formulas> <v:path o:extrusionok="f" gradientshapeok="t" o:connecttype="rect"/> <o:lock v:ext="edit" aspectratio="t"/> </v:shapetype><v:shape id="_x0000_i1025" type="#_x0000_t75" alt="" style='width:11.25pt; height:11.25pt'> <v:imagedata src="file:///C:/DOCUME~1/Joe/LOCALS~1/Temp/msoclip1/01/clip_image001.gif" o:href="http://www.m5board.com/ubb/smile.gif"/> </v:shape><![endif]--><!--[if !vml]-->:)<!--[endif]-->

Joe
 

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Re: Please answer a brake question for me....

Hey Joe-

Any opinion on the impact of diminished pad maetrial on brake fluid heating?

I've thought that taking the pads down to the limit can is bad since less pad material allows more heat to be transfered to the callipers... any truth, or is this a marginal consideration? (Notwithstanding your comments about general pad material condition..)

Adam
 

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Re: Please answer a brake question for me....

ard said:
Any opinion on the impact of diminished pad maetrial on brake fluid heating?

I've thought that taking the pads down to the limit can is bad since less pad material allows more heat to be transfered to the callipers... any truth, or is this a marginal consideration? (Notwithstanding your comments about general pad material condition..)
This is a valid concern for track use. Pro racers will typically discard a set of track pads when they are 50% worn, due to the increased heat transfer to the brake fluid. Pad material is a very effective thermal barrier. If you have marginal thermal capcity, it's a good idea to swap track pads when you are 50% worn.

That's the reason I carry Ti backing plates to drop in behind the pads on the StopTech and Brembo big brake kits. Titanium is a good thermal barrier and testing has shown up to a 70 degree F gradient across the Ti backing plates. These plates can allow you to get more out of a set of track pads, since you can run down to 25% or lower and not suffer brake fluid fade.

If you're talking about street use on a stock M5, then it's not a real consideration. The factory M5 brakes are not thermally stressed during street driving, right down to the 2mm pad thickness mark. That's when your pad wear sensor is destroyed by the rotor and the CHECK BRAKE LININGS message to appear on your dash. The most important thing is to keep your brake fluid fresh by flushing it at least every couple of years. I suggest annual fluid flushes on street-only cars and before each track event on track cars.
 

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Re: Please answer a brake question for me....

3mm should be the minimum depth of the pads!
 

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Re: Please answer a brake question for me....

ard said:
Hey Joe-

Any opinion on the impact of diminished pad maetrial on brake fluid heating?

I've thought that taking the pads down to the limit can is bad since less pad material allows more heat to be transfered to the callipers... any truth, or is this a marginal consideration? (Notwithstanding your comments about general pad material condition..)

Adam
Ard

I think Dave Z answered that better then I could.

Joe
 

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Re: Please answer a brake question for me....

Ahmed said:
3mm should be the minimum depth of the pads!
Even 0.5 mm is fine as long as you change the pads before they get all the way down to the metal backing plates.

The point is the sensors trigger at about 2mm. The pads start out at 14mm thick. (Not including backing plate.) If you get 30,000 miles out of your pads before the light goes off, that means 85.7% of your pads yielded 30,000 miles and you can expect another 5,000 miles from the remaining 14.3% before you reach metal on metal.

If I didn't do any of my own work and my mechanic told me that the pads were down to 4mm thick, I would certainly have him replace them, since I wouldn't want to bother making another appointment so soon. Time is money. On the other hand, there's no harm in letting the pads run down until the warning light goes off and then making an appointment for some date in the not-too-distant future. Nothing magical happens at the 3mm mark. The brakes continue to work right until the point that you start hearing that dreadful scraping sound as the last of the pad material goes away and you start scraping steel backing plates against cast iron rotors. 3mm is merely an arbitrary number.
 

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Re: Please answer a brake question for me....

DZeckhausen said:
Even 0.5 mm is fine as long as you change the pads before they get all the way down to the metal backing plates.

The point is the sensors trigger at about 2mm. The pads start out at 14mm thick. (Not including backing plate.) If you get 30,000 miles out of your pads before the light goes off, that means 85.7% of your pads yielded 30,000 miles and you can expect another 5,000 miles from the remaining 14.3% before you reach metal on metal.

If I didn't do any of my own work and my mechanic told me that the pads were down to 4mm thick, I would certainly have him replace them, since I wouldn't want to bother making another appointment so soon. Time is money. On the other hand, there's no harm in letting the pads run down until the warning light goes off and then making an appointment for some date in the not-too-distant future. Nothing magical happens at the 3mm mark. The brakes continue to work right until the point that you start hearing that dreadful scraping sound as the last of the pad material goes away and you start scraping steel backing plates against cast iron rotors. 3mm is merely an arbitrary number.
Another naive question: for normal street use, should rotors be changed at this point as well?
 

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Re: Please answer a brake question for me....

hughallen99 said:
Another naive question: for normal street use, should rotors be changed at this point as well?
Only if the rotors are worn down to (or near) their minimum allowable thickness. The front rotors started out at 32mm thick. If they get down to 30.4mm, then it's time to replace them. The rear rotors start life at 20mm thick. Discard thickness is 18.4mm.
 

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Re: Please answer a brake question for me....

DZeckhausen said:
Only if the rotors are worn down to (or near) their minimum allowable thickness. The front rotors started out at 32mm thick. If they get down to 30.4mm, then it's time to replace them. The rear rotors start life at 20mm thick. Discard thickness is 18.4mm.
Thanks Dave.

Hugh
 

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Re: Please answer a brake question for me....

DZeckhausen said:
Only if the rotors are worn down to (or near) their minimum allowable thickness. The front rotors started out at 32mm thick. If they get down to 30.4mm, then it's time to replace them. The rear rotors start life at 20mm thick. Discard thickness is 18.4mm.
I have a 2001 stock M5 with 50,000 miles which I purchased with 46,000 miles. I had a complete fluid change service when I got the car and at that time my SA said the brake pads where close. The CHECK BRAKE LINING came on once, but is now not on. I suppose they are just about time to be changed. I'm strictly a street driver with about 70% highway. What are the odds that the rotors are down to the minimum? I hate to pay that much. ??????
 

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Re: Please answer a brake question for me....

When BMW Dealer does a Brake Fluid flush, do they loosen each of the bleed screws on each tire?

Or do they just remove fluid from cylinder and replace?

How can I tell if in fact they did replace the fluid? hmmm
 

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Re: Please answer a brake question for me....

DZeckhausen said:
Only if the rotors are worn down to (or near) their minimum allowable thickness. The front rotors started out at 32mm thick. If they get down to 30.4mm, then it's time to replace them. The rear rotors start life at 20mm thick. Discard thickness is 18.4mm.
I once read in a BMW magazine that rotors and pads should always be changed at the same time??? Is there any truth to that opinion???
 

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Re: Please answer a brake question for me....

Beamer_usa said:
I once read in a BMW magazine that rotors and pads should always be changed at the same time??? Is there any truth to that opinion???
No. That generalization is false. Each pad and/or rotor swap should be evaluated and the parts changed based on an assessment of their condition. If you have a judder problem, deep scoring, or the rotors have worn to their minimum thickness, then by all means replace them. But if you're installing new pads and the rotors are within spec and not giving you any problems, it would be a waste of money to replace them.
 

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Re: Please answer a brake question for me....

Ocean's M5 said:
When BMW Dealer does a Brake Fluid flush, do they loosen each of the bleed screws on each tire?
They don't touch the tires. There are bleed screws on the calipers and yes, they do loosen each bleed screw to allow the old fluid to be expelled. Typically, BMW dealers do a pressure bleed, which is not as good as a manual bleed for getting all the air out of the system. See: http://www.zeckhausen.com/bleeding_brakes.htm
Or do they just remove fluid from cylinder and replace?
Since there's no fluid return path from the calipers, changing the fluid in the reservoir only would serve no purpose.
How can I tell if in fact they did replace the fluid? hmmm
You really can't. It's a matter of trust. Unless your old fluid is in such bad shape that it's discolored, there's no way to tell that the stuff in there is new. And the act of inspecting the fluid involves nearly as much work as the act of bleeding it. If you were going to go to that much trouble, you might as well bleed the brakes yourself. After all, you would have to remove the driver's side microfilter housing to gain access to the reservoir. Then you would have to remove each wheel and bleed a tiny bit of fluid so it could be inspected. No, you're going to have to take it on faith that they really did bleed your brakes. Of course, if your pedal feel changed noticably, that's a good indication they did something. Unfortunatly, the pedal feel often gets worse when a dealer bleeds your brakes.
 

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Re: Please answer a brake question for me....

Unfortunatly, the pedal feel often gets worse when a dealer bleeds your brakes.
I must be as old-fashioned as you, Dave. I have noticed the same thing and bleed them myself for that reason! And I use the old-fashioned two man method (actual, one man, one woman; I get my wife to work the pedal).
 

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Re: Please answer a brake question for me....

DZeckhausen said:
No, you're going to have to take it on faith that they really did bleed your brakes. Of course, if your pedal feel changed noticably, that's a good indication they did something. Unfortunatly, the pedal feel often gets worse when a dealer bleeds your brakes.
Dave,

On my 330i ZHP that I just bought in April, it is still covered under the full maintenance program, so I bought it to my local dealer for the 2 year brake flush. I specifically asked if they would flush the clutch slave cylinder also which they said they do.

This car only has 16k miles, and not much has been done to it since it was new. Last weekend my son and I put on new pads all around, and I noticed that the inside of the bleed nipples was COMPLETELY dry. It looked factory clean inside -- shiny clean, not a drop of moisture of any sort. The inside of the rubber covers was completely dry and clean also. I can only assume that they did not bleed the system at all. Wouldn't you agree? Otherwise they would have had to suck out the residual fluid that sits in the top of each nipple and dry the inside out with Brakeleen or something I would think. BTW, the nut edges do not appear to have ever had a wrench on them either. I have a call in to the service manager, so I'll see where this goes. I'm just getting ready to take my M5 in for some pre-warranty expiration items, and now I don't feel so good about that. :grrrr:

Chuck
 

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Re: Please answer a brake question for me....

DZeckhausen said:
You really can't. It's a matter of trust. Unless your old fluid is in such bad shape that it's discolored, there's no way to tell that the stuff in there is new.
No, you're going to have to take it on faith that they really did bleed your brakes. Of course, if your pedal feel changed noticably, that's a good indication they did something.
You can always bring your own fluid and switch between ATE Super Blue and Super Gold. If the color hasn't changed, they haven't flushed the brakes!!
Regards,
Jerry
 

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Beamer_usa said:
I once read in a BMW magazine that rotors and pads should always be changed at the same time??? Is there any truth to that opinion???
Yes and no.

I read a BMW trade rag that BMW publishes for their "independent dealer network" They recommend rotors with pads. There is a bunch of rationalization (rotors weight is being reduced to increase performance, hence there is less 'meat') but the two main reasons are (1) reduced 'customer bring backs' and (2) increased profits.

So while it may be true that BMW says this, it is not correct.

OTOH, how many folks will keep track of rotor wear and pad wear as independent variables? Safer to recommend replace it all when one hits the limit- I guess.
 
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