OT: Car Brakes Squeaking

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All pads will stop the car. Better pads will react to the heat differently and will not fade after repeated brakings. Pads originally were made from asbestos. Besides being a carcinogenic, they wore out extremely fast when used as disk pads. They also didn't react properly when subjected to the high temps of repeated braking. Then metallics came out to try and solve that problem. The first semi-metallics lasted longer, performed better but were noisy and harsh on the rotors. Now they have ceramic, kevlar which is not afftected by the heat as much, are easy on the rotors, put almost no dust on your wheels and guess what? They cost a hell of a lot more. So don't condemn people for spending more for pads than you do. There are reasons for it.
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Greetings,
And do most auto-manufactures use Kevlar pads on their new cars? Did you replace the pads on your car hot off the lot? You asked who used the $5/brake pads and I said the auto manufactures. You countered that the savings came from buying in bulk but it sounds to me that by your definition manufactures in fact save by using so called "crap pads!" You most certainly can pay more for z-Rated pads, etc. but believe it or not these "crap pads" for $5 per brake will perform equally well to the $50 per brake z-Rated pads available because the limiting factor on brake performance at any legal speed within my state is not the stopping power of the pad but instead the traction of the tires. My $5 per brake pads can provide MORE stopping power without overheating than my tire traction is able to handle. Different pads WILL NOT increase braking performance.
Hope this helps, William
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snipped-for-privacy@wdeans.com wrote:

having the hassle of repairing my car when you crash into it!
Different pads will not increase braking performance??!!??!?!?!?!? Where'd you get that from??
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Do you think that the $5/brake pads should be taken off the market?

I just explained that. Please explain to me how different brake pads could stop my car any faster so long as the ones I have are able to apply any amount of stopping power up to and including enough to lock the wheels.
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snipped-for-privacy@wdeans.com wrote:

the market.

different friction rates would apply?? Locking up the wheels is not a goal! Once you have locked up the wheels, you have lost control! Between applying brakes and the wheels locking up is stopping distance. Different friction materials will result in different stopping distances.
Now, if you still think locking up the wheels is a good thing, don't get behind me if you are driving in wet or icy conditions. If you feel that locking up your wheels is a good thing on a dry day in dry driving conditions, then please let me know how you have mapped out every oil slick on every road out there. Why do you think anti-lock brakes stop in a shorter distance than regular brakes?? Tire friction is not the best way to stop your car! Brakes are!
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I grow very tired of defending myself from statements I did not make. Locking up the wheels is a BAD thing; the coefficient of static friction is higher than the coefficient of dynamic friction. Having a pad capable of exerting the stopping power necessary to lock up your wheels is a GOOD thing. This is because the greatest deceleration is achieved by ALMOST locking up the wheels coming right up to the brink of locking them but NOT locking them.

I don't understand this nonsense. Can someone else please confirm that this is nonsense? What do oil slicks have to do with this? Are you saying locking your wheels on a dry day would be a good thing except for all those oil slicks?

No, apparently I didn't understand the science behind it. I am not trying to put words in your mouth but I think you were trying to say that different pads would produce different amounts of drag on the rotor with the same pressure exerted by the caliper because they are made of different materials? If so, you are correct, but it doesn't matter. My original statement was that any pad, no matter what the cost, would stop you in an equal distance so long as it was able to generate as much friction against the rotor as the tire traction would allow for without locking. This statement still holds true.
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snipped-for-privacy@wdeans.com wrote:

Okay, if you didn't say that, you didn't say it. I must have misunderstood.

Not nonsense if you had believed that locking up wheels was a good thing. Disregard.

Except that you leave too many variable out. Any pad?? Okay, I'll give you a set of my specially made teflon pads. Tell me you can generate enough pedal pressure to create the friction equal to a semi-metallic pad. You can't do it, the system isn't design for it. Bring it up to max pressure without locking? The teflon would give you lubricating properties. All pads are not created equal!
Or let's try this. Your pads have lost all their material. You are now stopping with brakes metal to metal. Bring your caliper pressure up to but not locking the wheel. That direct metal will give you a lot more "grab" than a pad with material. The friction happens quicker and more aggressively. You will slow quicker. In a shorter distance than pads with material.
Remember, we are talking about vehicle brake systems, not a "perfect" world where everyone reaches max pressure without locking. Different diameter rotors, different size pucks, different size pistons, etc, etc. Pad material makes a difference.
But enough, I don't like talking "work" on my weekends!
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OK, have a good weekend. I'll try to focus on answering JerryL's brake fade question.
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pads. When the pads heat up they will not stop the car normally.
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Greetings,

Yes, I have heard of 'brake fade'.
It is not just caused by excessive heat lowing the pad's coefficient of friction. In fact, brake fade is most often caused by boiling brake fluid. This is often because the brake fluid has absorbed water lowering its boiling point. Brake fade could be caused by carbon-dioxide coming out of solution within the brake fluid at high temperatures. Brake fade could be caused by outgassing of brand new brake pads (even expensive ones). Brake fade could be caused by the expansion of hot rubber brake hoses. There are probably many more.
Interestingly brake pads which perform better at higher temperatures perform worse at lower temperatures and cause markedly more rotor wear. This is why race car drivers need to "warm up" their brakes. Also interestingly the type of pads used don't have much effect on how much heat is generated. It generates the same amount of heat to slow a car from 65 to 0 no matter what pad is used. Most interestingly and most pertinent is that the $9.99 Semi-Metallic brake pads I purchased don't build up enough heat going from 65 to 0 to cause brake fade due to reduced coefficient of friction between the pad and the rotor. The coefficient of friction is still high enough to lock the wheels if I so chose throughout the entire deceleration.
If I sped up to 65 mph and then slammed on my brakes until I went to 0 and repeated the process several times I could cause brake fade. I don't have to worry about that because I would never do it. If with Kevlar-Carbon brakes I could repeat the process an additional two times before brake fade set in it's not worth a dollar extra to me.
Hope this helps, William
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snipped-for-privacy@wdeans.com wrote:

Envision this experiment:
Set up two axles so that you can apply the same constant external torque to each. Set up a hydraulic disc brake on each axle, each brake actuated by the same hydraulic line. Put pads of different materials on each brake. Now apply the external torque and apply hydraulic pressure.
The worse pads are the ones that lock their brake first.
You can actually do this experiment by putting pads of different materials on the front brakes of a non-ABS car. Probably it would be safer to run the experiment on rear brakes. Apply the brakes and check for skid marks. You will find that the side that skids has less stopping power---the front of the car will turn toward the side that doesn't skid.
You may not sue me if this experiment causes property damage, personal injury, or loss of life ...
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Greetings,
I ran through your experiment and it doesn't seem to work for me.

OK, the only way you could apply a constant external torque is by making the wheels rapidly accelerate with no brakes applied.

OK, this means that each pad will press against the rotor with equal force.

OK, I'll pretend the pads are Teflon and Asbestos.

As I apply hydraulic pressure the wheels will slow. The Teflon wheel will always spin faster than the Asbestos wheel at a fixed external torque and certain hydraulic pressure. Eventually the Asbestos pad wheel will stop once the hydraulic pressure is high enough. Later the Teflon pad wheel will come to a stop once the pressure is still higher.

Why? Why is the Asbestos pad worse than the Teflon one just because it locked the brakes first? I don't get it.

No you cannot. The front wheels will spin at the same speed and so the same external torque will not be exerted as suggested in your experiment (unless there is a different hydrolic pressure on each side which again is in violation of your experiment).
I was so happy when I almost thought you had it Matt. I think you have come the closest yet. William
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snipped-for-privacy@wdeans.com wrote:

I didn't quite get that right.
Let p be the hydraulic pressure at which the brake locks up and let c be the coefficient of sliding friction between the pad and the rotor at p - delta, where delta is small. The better brake is the one for which c * p is the larger.
I wrote and you seem to have missed:

skids has less stopping power---the front of the car will turn toward the side that doesn't skid.
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I didn't miss that. The side which skids first will be the Asbestos pad side, not the Teflon pad side making Asbestos worse than Teflon under your theory. Also, the car will turn towards the right OR the left when for example, the right wheel locks DEPENDING ON PAD MATERIAL because you have dislike pads. The tires sliding on the road might still be providing more drag than the Teflon pad at the pressure the Asbestos pad would lock the brakes resulting in the car turning TOWARDS the skidding tire. The car is guaranteed to turn AWAY from the skidding tire with like pads but could go either way with dislike pads. Dislike pads need dislike pressures to provide the same amount of friction (achievable on an anti lock brake system which this the test car you specifically stated is not).

Matt, I am sorry but I think you have the "coefficient of sliding friction" partially confused. The "coefficient of sliding friction" for two materials is the same regardless of pressure. In fact, if two materials are not even touching their coefficient of sliding friction is the same as if those materials are forcefully pressed together while sliding past each other. That is not what the "coefficient of sliding friction" is.
Sometimes I have problems articulating myself as well. Obviously, because there are still people who disagree with me :-)
William
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How is this thread related to home repair?
<Theoretical discussion of friction in the context of automotive braking systems snipped.>
jim
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Hypocrite. You complain this is not on topic, yet you have the balls to attempt to post a binary attachment in another post. Binary is binary and does not belong in this group no matter the size.
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jim evans wrote:

Any thread is relevant to any group if the OP precedes the title by "OT".
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snipped-for-privacy@wdeans.com wrote:

But not if you increase the brake pressure to just less than what would lock up the teflon brake.
Please state whether you agree that either brake will do better at a pressure slightly less than what causes it to lock up and skid.

'unlike' not 'dislike'
Wheels with like pads will skid at about the same pressure.
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If you can create pressure causing friction slightly less than enough to lock up the brakes without causing brake failure for the duration of the stop all brake pad materials will perform equally well.
At legal speeds in my state the $9.99 semi-metallic pads perform as well as Kevlar and they don't eat up my rotors as fast. You could of course heat them up until they failed before Kevlar with a series of rapid decelerations but I would never do that. Someone said something about a mountain. Drop your car into low gear and there is not a mountain in the USA which would cause my $9.99 semi-metallic pads to fail.
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snipped-for-privacy@wdeans.com wrote:

I don't think you have dealt with that c * (p-delta) expression that I mentioned. You have to notice that both c and p depend on the pad material, p-delta being the pressure just prior to lockup and c being the coefficient of sliding friction prior to lockup.
I am not an expert, but I think you are wrong. I don't think you are an expert either. Are you saying that the expensive pads are some kind of gimmick? Maybe supported by some grand sinister propaganda effort? I suppose it's possible, but how about citing some expert sources that support your claim? There must be some---maybe put out by the companies that make $9.99 pads.
And to be fair to yourself, I think maybe you ought to test your claim by putting pads of different materials on opposite-side brakes. Just don't do it in a top-heavy vehicle or on a busy road. Standard disclaimers apply. I guess you are saying that the driver won't be able to detect that the brake pads don't match.
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