I had a set of rotors/pads on my 528e that were down right scary in wet weather. 1st touch of brake pedal did nothing to slow the car. 2nd touch was much more effective. I'm guessing I was experiencing pad float. Thanks for your explanation, Blue Max.
Looking for some "bulletproof" brake rotors
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I'm extremely pleased with the Akebono pads. Nice progressive stopping power, excellent bite when I really need it.
As for rotors, I've used Brembo and ATE solid rotors. Both are good. The ATE rotors said "Made in Italy" on the packaging.
It's heavy, over twice the density of steel. There are several other reasons. Someone else can list them.
Like someone already said, lotsa Subaru users speak highly of this company. Also recommended by my local Subaru dealer.
http://www.dba.com.au/2006/default.asp
heres my take on it. theres no such thing as bullet proof rotors. (but you can spend alot trying). ALL rotors eventually wear out, need resurfacing, etc.
why not spring for a set of cheap rotors that have a lifetime warranty? this way whenever you feel like you need new rotors you can go get yours replaced for free. this way 1 year down the road, 5 years, heck 10 years down, you can still be running on new rotors.
why not spring for a set of cheap rotors that have a lifetime warranty? this way whenever you feel like you need new rotors you can go get yours replaced for free. this way 1 year down the road, 5 years, heck 10 years down, you can still be running on new rotors.
I'll throw my 0.02 cents in while I'm at it. My geo prizm went through a couple of brake rotors that I had warped. Napa generously traded my lifetime rotors for their top of the line rotors with cooling vanes cast on th inside. The look alot like DBA'S (Disk Brake Australia) kangaroo paw design but at a vastly cheaper price. I think DBA's are up to $200+ a piece. They seem to work well, and the list price is only $60ish per rotor, very reasonable.
EBC makes good pads as well as rotors
BlueMax, where the heck have you been all my life? These posts are amazing! So much better than the usual "I bought some of them there rotors at AutoZone and they work great on my 82 Citation."
EBC Green pads totally destroyed my new rotors. First set were great but they must have changed compound before I purchased 2nd set and sayonara rotors. Be careful folks
Kestas
Staff member
Most brake rotors are made of gray cast iron. It is hard to screw up the metallurgy of cast iron (though I imagine some overseas manufacturers will find a way to screw it up). If a brake rotor is giving problems, it was either machined wrong, installed wrong, the hub mating surface isn't flat, or there are problems with stress relief within the rotor. If you have a set of rotors that warp easily, even after turning to true them up, they may be salvaged by stress relief heat treatment. This involves gradually heating the rotor to 1000-1200°F, then cool in the furnace. This will give you a "bulletproof" rotor. After that, you'll have to look elsewhere other than the rotors themselves for warpage problems. Of course this can only work if you have access to such a furnace.
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Kestas, what do you think of the cryogenic treatments that some companies are performing on their rotors? Do you think it would help the iron to be more stable or have any benefit?
Kestas
Staff member
I see no metallurgical basis for cryogenic treatments to work on soft cast iron. Nothing will change within the microstructure when going from room temperature to cryogenic temperature. I know the NARCAR folk use it, but a lot of what they do is based on their attitude as opposed to good sound judgement.
The heat treatment I prescribed is the accepted method of stablizing the metal.
The only valid use for cryotempering metal is with quench-and-tempered steel, such as tool steels and the gun metals you're personally familiar with. Nearly all other uses are just snake oil.
The heat treatment I prescribed is the accepted method of stablizing the metal.
The only valid use for cryotempering metal is with quench-and-tempered steel, such as tool steels and the gun metals you're personally familiar with. Nearly all other uses are just snake oil.
BTW, I oticed that in all this, I seem to have missed mention about 'warped' rotors.
In truth, brake rotors rarely ever warp. The most common cause of brake judder is uneven pad deposits. This can happen if you don't bed the brakes in properly or if you overheat the brake system taking the pads past their MOT.
As Kestas has also mentioned, uneven pad deposits can also form if the rotor to hub mating surface is not flat (this is more prone to happen on old vehicles where rust can develop on the hub. If not cleaned off properly before the new rotors are installed, this can cause problems).
I have really only ever seen ONE single incidence of a warped brake rotor. It was an acquaintance of mine who, as it turns out, had a bad habit of resting her left foot on the brake pedal of her new (new to her) auto transmission car while driving. Dragging the brakes like that not only boiled the brake fluid and killed the brake pads, it actually warped the rotors, as I've said, the first and only time I've ever seen something I couold confirm as a warped rotor. A wavy bluish temper line developed between the rotor face and the hat.
To prevent brake judder, make sure the hub-rotor mounting surfaces are clean. Use good brake pads (appropriate for your application for the weight and speed of the vehicle and your aggressiveness behind the wheel) and make sure to properly bed them in. Don't drag the brakes.
For instance, when coming down a long descent, do not ride the brakes all the way down to maintain your speed. The proper technique is to downshift to a low gear allowing engine braking to maintain the vehicle's speed (while the engine turns at a reasonable rpm. For this application, you shouldn't be engine braking so you hear the engine screaming at, or even near redline. The engine rpms should be at cruising rates, i.e. between 2000-4000rpm).
This can be done easily with a manual of course and also with an automatic (that's why auto transmission selectors have 1, 2, 3 and Drive). If the gradient is steep enough that the car continues to pick up speed, the brakes should be applied so the car slows below your target speed and then the brakes allowed to cool with your foot off the pedal as the car begins to pick up speed again. Keeping your foot on the brake pedal all the way down the mountain is one good way to develop brake system problems.
If uneven pad deposition occurs resulting in brake judder, if caught early enough, it may be possible to remedy the problem by having the rotors turned and making sure that the cause of uneven pad deposition is removed (uneven hub/rotor interface or cheap pads etc.). However if the problem has gone on for some time, the rotors may need to be replaced. Uneven pad deposits lead to uneven rotor temperatures with the 'high' areas experiencing increasingly elevated temperatures. If the temperatures get high enough, they can cause the formation of cementite in those particular areas which will permanently change the way that section of the rotor behaves compared to the other parts of the rotor, resulting in the brake judder returning soon after having the rotors turned.
Max
In truth, brake rotors rarely ever warp. The most common cause of brake judder is uneven pad deposits. This can happen if you don't bed the brakes in properly or if you overheat the brake system taking the pads past their MOT.
As Kestas has also mentioned, uneven pad deposits can also form if the rotor to hub mating surface is not flat (this is more prone to happen on old vehicles where rust can develop on the hub. If not cleaned off properly before the new rotors are installed, this can cause problems).
I have really only ever seen ONE single incidence of a warped brake rotor. It was an acquaintance of mine who, as it turns out, had a bad habit of resting her left foot on the brake pedal of her new (new to her) auto transmission car while driving. Dragging the brakes like that not only boiled the brake fluid and killed the brake pads, it actually warped the rotors, as I've said, the first and only time I've ever seen something I couold confirm as a warped rotor. A wavy bluish temper line developed between the rotor face and the hat.
To prevent brake judder, make sure the hub-rotor mounting surfaces are clean. Use good brake pads (appropriate for your application for the weight and speed of the vehicle and your aggressiveness behind the wheel) and make sure to properly bed them in. Don't drag the brakes.
For instance, when coming down a long descent, do not ride the brakes all the way down to maintain your speed. The proper technique is to downshift to a low gear allowing engine braking to maintain the vehicle's speed (while the engine turns at a reasonable rpm. For this application, you shouldn't be engine braking so you hear the engine screaming at, or even near redline. The engine rpms should be at cruising rates, i.e. between 2000-4000rpm).
This can be done easily with a manual of course and also with an automatic (that's why auto transmission selectors have 1, 2, 3 and Drive). If the gradient is steep enough that the car continues to pick up speed, the brakes should be applied so the car slows below your target speed and then the brakes allowed to cool with your foot off the pedal as the car begins to pick up speed again. Keeping your foot on the brake pedal all the way down the mountain is one good way to develop brake system problems.
If uneven pad deposition occurs resulting in brake judder, if caught early enough, it may be possible to remedy the problem by having the rotors turned and making sure that the cause of uneven pad deposition is removed (uneven hub/rotor interface or cheap pads etc.). However if the problem has gone on for some time, the rotors may need to be replaced. Uneven pad deposits lead to uneven rotor temperatures with the 'high' areas experiencing increasingly elevated temperatures. If the temperatures get high enough, they can cause the formation of cementite in those particular areas which will permanently change the way that section of the rotor behaves compared to the other parts of the rotor, resulting in the brake judder returning soon after having the rotors turned.
Max
Kestas
Staff member
Just to add a side note. Our company makes bearing hub units for the automotive industry. There's a push by the manufacturers to increase the flatness and reduce wobble on the rotor mating surface of the hub. They're targeting 20-micron runout. This is to decrease knockback of the brake pads, which reduces brake application time, brake judder, and increases overall brake feel. This is also presenting a number of engineering challenges for our company.
So, as DIYers, do your part, use a wire brush, and make sure the rotor mount surfaces are clean and flat before installation.
So, as DIYers, do your part, use a wire brush, and make sure the rotor mount surfaces are clean and flat before installation.
Thanks Kestas. Do you have a link or explanation as to what the cryo treatment does to the metal? I've never heard a really good description of the theory.
Thanks again.
Kestas
Staff member
The basic premise behind cryotempering is to convert retained austenite to martensite in quench and tempered steels. Very few other alloys have this phenomenon.
Cryotempering is done for two reasons. One is to make the steel a bit harder (important at higher levels of retained austenite). The other - and in my opinion more important reason - is to "head off" this phase change so it doesn't occur during use, as often happens when a part is placed into service and loads are put on it. The phase change is accompanied by a volume change, which can warp the metal.
Common applications are: precision bearings, tools, broaches, guns, and any quench and tempered steels that are small and have expensive machining or tight tolerances. The number one use for cryotempering is cutting tools where the tool life can be extended 2 to 5 times the normal life.
That's it in a nutshell without going into too much detail.
Cryotempering is done for two reasons. One is to make the steel a bit harder (important at higher levels of retained austenite). The other - and in my opinion more important reason - is to "head off" this phase change so it doesn't occur during use, as often happens when a part is placed into service and loads are put on it. The phase change is accompanied by a volume change, which can warp the metal.
Common applications are: precision bearings, tools, broaches, guns, and any quench and tempered steels that are small and have expensive machining or tight tolerances. The number one use for cryotempering is cutting tools where the tool life can be extended 2 to 5 times the normal life.
That's it in a nutshell without going into too much detail.
Kestas, nice explanation. I've seen others in semi-technical publications like car rags go on for pages without actually saying that much.
Hmmm...yes, controlling warpage would be very useful in precision rifle barrels which would explain why it is used for that Ap.
Kestas
Staff member
I've read the same garbage. Once they start talking about "aligning molecules" or "rearranging the atoms" my eyes glaze over and I realize they have no idea what they're talking about.
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