OT: Car Brakes Squeaking

[William.Deans]

Reach for that maturity Henslee.

[G Henslee]

Reach for that little red ball Fido.

[anoldfart2]

Since my computer is in my house, how do I install more memory in my computer?

[Matt]

It looks like William is right about this. It seems that under normal circumstances braking is limited by static friction between the tires and the road, not by sliding or static friction between the pad and the rotor. The coefficient of static friction between the road and the tire determines a maximum torque that the brakes should apply to the wheel. It would seem that ABSes increase the frictional forces between pads and rotors until the wheels lock, then they let off so that the wheels _don't_ lock up. Any pads can produce enough friction to lock the wheels, so it is the tire traction that matters. Unless of course the brakes overheat and begin to fade. I guess it doesn't matter unless you might have to hurry down a tall mountain.

[Edwin Pawlowski]

She park the car in the garage that is part of the house.

[Matt]

Uh oh. I think I may have to retract some of the above ...

The amount of sliding frictional force that can be developed between pad and rotor depends on the materials. The maximum sliding torque will differ. In other words some pads may cause the brakes to lock up and the tires to skid at lower torques than other pads. Any pads can lock up the wheels, but the better pads can keep the wheels turning while applying large torques.

[Matt]

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 ...

[CL (dnoyeB) Gilbert]

There are metal tabs on brake pads that make noise to tell you its time to replace them. Brake shoes dont have this.

First time the make noise is to tell you to replace them.

The noise will eventually go away usually.

Second time they make noise is because you failed to replace them and are now grinding against your rotors, metal against metal.

sometimes metalic brakes can squeek a bit when breaking which is normal for them. Just have to get used to understand each sound. This starts by taking to good mechanic when you hear it. Find ONE good mechanic you can trust and stick with him/her.

[William.Deans]

skids has less

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).

at p[ressure] - delta, where

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

[William.Deans]

Greetings JerryL,

You asked about brake fade yesterday in a previous post and I responded to you in some depth late last night. Please read my response there.

Hope this helps, William

[Duane Bozarth]

....for a given rotor/pad material combination...

[JerryL]

Regardless of type (disk or drum), your brakes work by pressing a non-revolving material against a revolving material and, as a result, converting (via friction) the energy from the revolving material into heat. The harder the materials are pressed together, the greater the friction and, as a result, the greater the rate of conversion - i.e., the more braking force applied, the quicker you slow down the revolutions of the wheels, and the hotter the brakes become.

The brakes are also designed to radiate the resulting heat into the environment and, thus, allow the brakes to cool down quickly after they are no longer being used. This is a very important part of their design because the braking material used loses efficiency (reduced friction) with high heat. Indeed, if the braking material gets too hot it can be permanently damaged (it will glaze.)

[Matt]

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.

[jim evans]

How is this thread related to home repair?

jim

[Edwin Pawlowski]

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.

[Matt]

Any thread is relevant to any group if the OP precedes the title by "OT".

[do_not_spam_me]

That's better, but beginners are much more likley to get in trouble with stuck bleeder screws, including rounding or shearing them off, than with damaging master cylinders.

Some manufacturers, including Nissan, specify a thin coating of high-temperature grease on the backs of the brake pads and other metal-to-metal contact points.

[Mark and Kim Smith]

Then beginners shouldn't do the job until they have the proper tools and know what they are doing. Plus, if proper maintenance is being done, beginners won't have a problem with bleeder screws. Bleeder screws are there for a reason.

[Matt]

skids has less

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.

[William.Deans]

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.