Brake wear

[Blauweisser]

Had new pads and disks replaced all round on my 125i manual after 65k km. A bit surprised, since I'm very light on brakes by using gears for virtually all stopping. The mechanic at BMTS here in Brisbane said that BMW OEM disks are pretty soft, presumably to ensure good stopping performance. Had them replaced with after-market disks of German origin, plus ceramic pads. After a couple of weeks city driving, I'm quite happy with the performance. Nice progressive feel, no grabbing, and the wheels seem to be much cleaner (presumably since the ceramics use copper instead of iron as the heat conductive medium). Hopefully they last longer than the originals.

Another thing I have noticed is that the after-market disks don't seem to rust so much when I wash the car. With the OEM disks, a rust film would form rapidly. That would indicate a different steel alloy, I suppose.

[flinchy]

BMTS told me at 100,000km i wouldn't make another 5,000km - i drive the same as you do, engine brake mainly.

i made another 30,000km and still had a couple mm of pads.. loads left on the rotors.

i wouldn't necessarily trust what they say about brakes.

[jksgoh]

I just had a service down at a local dealer, said my 2 front discs and pads need replacing. I've just done 59xxx km.
They just said it was "low" but weren't able to give me a figure on it.
Anyway, they want to charge me $449 for the pads, and $351 for the rotors fitted.
What sort of price did you guys pay, and how do i measure how much you have left on the rotors and pads?

[flinchy]

Originally Posted by jksgoh

I just had a service down at a local dealer, said my 2 front discs and pads need replacing. I've just done 59xxx km.
They just said it was "low" but weren't able to give me a figure on it.
Anyway, they want to charge me $449 for the pads, and $351 for the rotors fitted.
What sort of price did you guys pay, and how do i measure how much you have left on the rotors and pads?

Rotors have a minimum thickness you'll need a ruler to measure

Pads you can look at how much is left before its just backing plate

If theres enough left (rotors should last at least 2 sets of pads)... Parts alone: Pads from USA for like $100-$150, rotors are not much more.

And a garage should take no more than an hour at it

[drjekl]

Originally Posted by flinchy

Rotors have a minimum thickness you'll need a ruler to measure

You'll need some micrometers for this, not verniers or a ruler (as there is a tiny lip on the outside edge of the rotor where the pad doesn't come in contact with the rotor)

[drjekl]

Originally Posted by Blauweisser

Had new pads and disks replaced all round on my 125i manual after 65k km. A bit surprised, since I'm very light on brakes by using gears for virtually all stopping. The mechanic at BMTS here in Brisbane said that BMW OEM disks are pretty soft, presumably to ensure good stopping performance. Had them replaced with after-market disks of German origin, plus ceramic pads. After a couple of weeks city driving, I'm quite happy with the performance. Nice progressive feel, no grabbing, and the wheels seem to be much cleaner (presumably since the ceramics use copper instead of iron as the heat conductive medium). Hopefully they last longer than the originals.

Another thing I have noticed is that the after-market disks don't seem to rust so much when I wash the car. With the OEM disks, a rust film would form rapidly. That would indicate a different steel alloy, I suppose.

I have used ceramic pads before and didn't really like them as the pedal feel wasn't as good, but alas i wash my cars weekly anyway so i don't get a great deal of brake dust buildup.

Yes you're correct in assuming the chemical composition of the rotors are different from oem, a high Fe content in the oem rotors is what causes them to corrode whilst this isn't aesthetically pleasing the higher Fe content is great for pedal feel & iron rotor has a higher rate of friction and improved thermal resistance (less likely to warp)

[flinchy]

Originally Posted by drjekl

You'll need some micrometers for this, not verniers or a ruler (as there is a tiny lip on the outside edge of the rotor where the pad doesn't come in contact with the rotor)

if you need THAT level of accuracy in the measurement, it's high time to replace them anyway lol

Originally Posted by drjekl

I have used ceramic pads before and didn't really like them as the pedal feel wasn't as good, but alas i wash my cars weekly anyway so i don't get a great deal of brake dust buildup.

Yes you're correct in assuming the chemical composition of the rotors are different from oem, a high Fe content in the oem rotors is what causes them to corrode whilst this isn't aesthetically pleasing the higher Fe content is great for pedal feel & iron rotor has a higher rate of friction and improved thermal resistance (less likely to warp)

it's almost impossible for a rotor to warp, and you don't want a rotor to be resistant to heat, iron is actually better at absorbing heat, hence they make good rotors.. absorbing the friction of the pads quickly!

i'm not entirely aware of any rotor being not cast iron, unless they're ceramic/carbon ceramic or something? Even brembos are simply high quality cast iron.

[drjekl]

Originally Posted by flinchy

using a ruler on the face of the rotor with another ruler flat along the hub mount part rather than the side gets around any lip issues if you don't have a micrometer - mine were worn evenly to the edge though, there was only a lip on the inside part of the rotor

if you need THAT level of accuracy in the measurement, it's high time to replace them anyway lol




it's almost impossible for a rotor to warp, and you don't want a rotor to be resistant to heat, iron is actually better at absorbing heat, hence they make good rotors.. absorbing the friction of the pads quickly!

i'm not entirely aware of any rotor being not cast iron, unless they're ceramic/carbon ceramic or something? Even brembos are simply high quality cast iron.

Ahh jeez were you drunk dude when you typed this? haha

[flinchy]

Originally Posted by drjekl

Ahh jeez were you drunk dude when you typed this? haha

haha, no not drunk

hold on i'll proof-read it

..

yeah i had trouble explaining it, and i can't find the pic i found in the first place. Just disregard it. It worked for me when comparing my used ones to the new ones is all.

either way, unless you want to spend $50 on a micrometer just to make sure you can get another pad change out of the rotor... if you think it's getting low, just spend the not-all-too-much money it costs to replace them.

[Blauweisser]

A little disturbed about BMTS, Flinchy, however, we're moving interstate (driving down to NSW) and I will require a roadworthy within a few months prior to re-registration. I didn't want any issues with the car, as I'll be busy enough getting our house sorted out down there. The mechanic told me at my last yearly service that the rears would need replacing at the next service. He reported at this year's service that the front rotors looked pretty chewed, and it might be a near thing if they were still thick enough after re-facing.

Thanks for your comments, drjekyl. You reminded me that I know nothing of brake rotor composition. This article gave me a quick tutorial: http://www.sae.org/events/bce/tutorial-ihm.pdf
It seems that all commonly available rotors are fabricated from "gray" (cast) iron, with varying carbon contents and processing conditions strongly influencing the range of properties considered desirable. Rusting appears to be dependent on the microstructure and chemical composition of the rotor. BMW appears to specify a material which gives it the range of properties it considers most desirable.

[drjekl]

Originally Posted by flinchy

it's almost impossible for a rotor to warp.

Hmm I disagree!!!

Originally Posted by flinchy

i'm not entirely aware of any rotor being not cast iron, unless they're ceramic/carbon ceramic or something? Even brembos are simply high quality cast iron.

Yes I never stated that the rotors werent cast Fe, it's the chemical composition which is different of the oem rotors v's aftermarket items.

Originally Posted by flinchy

either way, unless you want to spend $50 on a micrometer just to make sure you can get another pad change out of the rotor... if you think it's getting low, just spend the not-all-too-much money it costs to replace them.

You can buy a set of 0-25mm mic's for $10, whereas rotors are a few hundred each for some decent quality rotors.

[jksgoh]

So how much have you guys previously paid to replace the front rotors and pads on a 125i?

[drjekl]

Originally Posted by Blauweisser

A little disturbed about BMTS, Flinchy, however, we're moving interstate (driving down to NSW) and I will require a roadworthy within a few months prior to re-registration. I didn't want any issues with the car, as I'll be busy enough getting our house sorted out down there. The mechanic told me at my last yearly service that the rears would need replacing at the next service. He reported at this year's service that the front rotors looked pretty chewed, and it might be a near thing if they were still thick enough after re-facing.

Thanks for your comments, drjekyl. You reminded me that I know nothing of brake rotor composition. This article gave me a quick tutorial: http://www.sae.org/events/bce/tutorial-ihm.pdf
It seems that all commonly available rotors are fabricated from "gray" (cast) iron, with varying carbon contents and processing conditions strongly influencing the range of properties considered desirable. Rusting appears to be dependent on the microstructure and chemical composition of the rotor. BMW appears to specify a material which gives it the range of properties it considers most desirable.

I'm sure you would pass rego fine, as long as your brakes are functioning OK.

That article is a fairly in depth insight in basic metallurgy and would take some time to understand the phase transformations, terms and terminology!!

[flinchy]

Originally Posted by drjekl

Hmm I disagree!!!



Yes I never stated that the rotors werent cast Fe, it's the chemical composition which is different of the oem rotors v's aftermarket items.



You can buy a set of 0-25mm mic's for $10, whereas rotors are a few hundred each for some decent quality rotors.

http://www.stoptech.com/technical-su...nd-other-myths

stoptech disagrees with your disagreement! :P - Even if you got it glowing then doused it in a few liters of water.. MAYBE then?

or you might have a rotor that's already out of spec from factory (too much runout say) that's installed, used, and then goes further out of spec with uneven wear.

And yeah fair enough, mettalurgy is one of the most complicated areas i've ever encountered, so many different alloys/compositions/states of any given material, that may as well be entirely unrelated.

wait, $10? where from, i tried having a look and could only find 50mm for $50 as the cheapest. I'd love to grab a set for $10!

[drjekl]

Originally Posted by flinchy

http://www.stoptech.com/technical-su...nd-other-myths

stoptech disagrees with your disagreement! :P - Even if you got it glowing then doused it in a few liters of water.. MAYBE then?

or you might have a rotor that's already out of spec from factory (too much runout say) that's installed, used, and then goes further out of spec with uneven wear.

And yeah fair enough, mettalurgy is one of the most complicated areas i've ever encountered, so many different alloys/compositions/states of any given material, that may as well be entirely unrelated.

wait, $10? where from, i tried having a look and could only find 50mm for $50 as the cheapest. I'd love to grab a set for $10!

http://www.ebay.com.au/itm/Mechanist...ad91852&_uhb=1

Whilst I would much rather my mitutoyo mics, these would be perfectly fine to measure brake rotors with.

[flinchy]

ohh no idea why i didn't check ebay

thanks, always good to add another tool to the kit.

[Nugget]

Originally Posted by drjekl

http://www.ebay.com.au/itm/Mechanist...ad91852&_uhb=1

Whilst I would much rather my mitutoyo mics, these would be perfectly fine to measure brake rotors with.

How thick are the stock rotors?
That only measures up to 25mm.
My stoptech rotors started as 32mm thick, and after a fair amount of abuse are now 31.5mm thick with lots of heat checking. Apparently they are good until 30mm but will be replaced before then if the heat checking turns into cracking.

[drjekl]

Originally Posted by Nugget

How thick are the stock rotors?
That only measures up to 25mm.
My stoptech rotors started as 32mm thick, and after a fair amount of abuse are now 31.5mm thick with lots of heat checking. Apparently they are good until 30mm but will be replaced before then if the heat checking turns into cracking.

I'm certain NA rotors are <25mm (OP has a 125i) but I know for sure my m3 rotors are >25mm (min thickness was ~ 28mm)

[samchuang33]

Originally Posted by Blauweisser

Had new pads and disks replaced all round on my 125i manual after 65k km. A bit surprised, since I'm very light on brakes by using gears for virtually all stopping. The mechanic at BMTS here in Brisbane said that BMW OEM disks are pretty soft, presumably to ensure good stopping performance. Had them replaced with after-market disks of German origin, plus ceramic pads. After a couple of weeks city driving, I'm quite happy with the performance. Nice progressive feel, no grabbing, and the wheels seem to be much cleaner (presumably since the ceramics use copper instead of iron as the heat conductive medium). Hopefully they last longer than the originals.

Another thing I have noticed is that the after-market disks don't seem to rust so much when I wash the car. With the OEM disks, a rust film would form rapidly. That would indicate a different steel alloy, I suppose.

What ceramic pad and aftermarket disc did u use?

How much if u don't mind me asking? I just change akebono ceramic pad with EBC disc on a 530d for $1500 so curious to see how much u paid.

[Blauweisser]

Originally Posted by samchuang33

What ceramic pad and aftermarket disc did u use?

How much if u don't mind me asking? I just change akebono ceramic pad with EBC disc on a 530d for $1500 so curious to see how much u paid.

I'll have to ask about the brands, but the total cost for new rotors and ceramic pads was around $1500. I'll report back when I get the information.