breetai

Today I'm going to cover what I feel to be the most important system on an automobile. It's my experience that it's also an often overlooked area, especially to beginners, and those on a budget, when tuning/upgrading a cars performace. Photobucket is down right now, so you'll have to follow links to the pictures. I'll embed the photos later. All photos remain the property of the website they are borrowed from.

Brakes.

The brakes on a car work by turning mechanical force into friction. There are two basic categories of brakes. Power assisted, and non assisted. Under those categories are the sub-categories of disk, and drum. Disk brakes can further be broken down into unvented, vented, and drilled/slotted.

Unassisted: Unassisted brakes use no mechanical multipliers to assist the depression of the brake pedal to turn that force into stopping force. When you press the pedal you depress an hydraulic piston pushing the hydraulic fluid to the wheel cylinders(to my knowledge there aren't disk brakes made that aren't power assisted due to the amount of pressure required to effectively use them), thus pressing the brake shoe against the drum, creating friction and arresting the vehicles forward momentum.

Power assisted brakes: Power assisted brakes use one or more mechanical systems to amplify the pressure of your foot on the pedal to create more pressure in the braking system, thus creating more force on the brakes i.e; more friction, and better stopping power.

The two most common power amplifying systems for power assisted brakes are vacuum assisted, and hydraulic assisted.

Vacuum assisted brakes tap the motors vacuum to "pull" a diaphram connected to the piston inside the master cylinder, creating more force than the "naked" foot alone can create.

Hydraulic assisted brakes use either a slave pump run off the accesory pully system on the motor, or lines from the power steering pump to assist in much the same manner as vaccum assisted. Hydraulic assisted brakes are most commonly found on diesel motors (since diesels create less usable vacuum than gas motors do), and some heavy duty gas applications.

Drum brakes: Drum brakes route the hydraulic pressure into a two way (double ended might be a better description) hydraulic piston bolted to the axle or spindle which "spreads" the shoes outward to contact a rotating drum (free floating, held in place with the wheel studs/nuts).



Drum brakes are very inefficient for a number of reasons.

1. There is limited space inside the drum to place parts, necessitating small(when compared to the piston in a disk brake) hydraulic pistons to enact the force on the shoes.

2. Drums are subject to deformation due to the forces of the shoes on the drum.

3. Drums heat up very quickly, and stay hot longer, creating "brake fade".

4. Drum brakes weigh quite a bit more than disk brakes.

Disk brakes: Disk brakes route the fluid pressure to a piston hard mounted inside a semi-floating caliper, one brake pad installed on the moving end of the piston (interior of the disk), the other pad on the other side of the caliper (exterior of the disk). When the piston extends, pushing the pad onto the free floating rotor(held in place again, by the wheel studs/nuts) the caliper pushes the opposite direction of the piston "pulling" the outside pad against the other side of the disk, in effect "squishing" the disk between the two pads.



Disk brakes are significantly more efficient than drum brakes.

If that's the case Jason, why don't ALL cars have 4 wheel disk brakes?

I can't give you a good answer. I have no idea, other than parking brakes on drum equipped cars are a lot easier to design and install.

Unvented disk brakes: Unvented disk brakes use a solid disk of steel mounted between the pads. More effecient than drum brakes in creating friction. Only marginally more efficient in dissipating heat caused by braking, since both sides of the disk are being heated.

Vented disks: Vented disks are as efficient in creating friction as unvented disks. Vented disks use two disks with "webs" between them creating an air gap between the "inside" of the friction surfaces. Vented disks cool much better due to the air gap, and greater surface areas between the disks that are un touched by the friction material of the pads.

Drilled/slotted Vented disks: Drilled and slotted vented disks have slots milled into the friction surface, either at a tangent to, or along the radii of the disk. These slots add surface area to the disk, allowing better cooling. More important than that the slots allow a place for the gasses created when the friction material of the pad heats up to go, rather than being trapped between the pad and disk. The edges of the slot also act to slough off more (ever so slightly) friction material, creating more friction.



Drilled rotors act in exactly the same way, but by a slightly different means, with holes drilled through the rotors.



What brakes offer the most stopping power?

Stopping power is gained in the order of: Unassisted brakes. Assisted drum, assisted unvented disk, assisted vented disk, assisted vented drilled/slotted.

There is some argument as to which is better, drilled, or slotted. I'm unable to say at this time which is definitively better.

There are other means to creating more stopping power out of disk brakes. Larger diameter *correction* Disks net more friction surface area, and marginally better cooling than disks of the same type, but a smaller size.

Multi piston calipers are more efficient than single piston calipers and create more pressure on the friction surfaces.

Richard

If you put image tags you can hot link the images.


[img]http://www.impalaforums.com/myimage.jpg[/img]

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breetai

Thanks richard. See, even a know it all like myself learns something once and a while, lol.

Gregg-O

"There is some argument as to which is better, drilled, or slotted. I'm unable to say at this time which is definitively better."

Actually, neither one offers better stopping power, each one has less friction surface than a plain rotor. On our heavy cars the best upgarde is a larger rotor, & a multi-piston caliper.

Drilled and/or slotted is a ricer 'bling' thing, they also work good on a light race car, that will have the rotors changed every few races.

breetai

As said in my post the main reason to drill or slot a rotor is to vent gasses better and to help with cooling. Though they may not afford a significant difference in "one stop" stopping power, they do cool better and are less succeptible to "brake fade", which occurs after many hard braking sessions while driving on a track, or deserted curvy back road.

For a daily driven street car, that won't be run hard, and subjected to the type of braking seen at a track, drilled or slotted rotors may not be worth the money. For a car that is driven at a track, autocross, or otherwise "flogged" on a regular basis, they are a good upgrade. I put a set on my 86 VW golf autocrosser I had, and the difference was remarkable under those conditions. It was as drastic a change as going from the stock unvented disks, to the GTI vented disks. They are also a good upgrade on a pickup or other vehicle that will be used to tow, since those vehicles brakes are subject to greater amounts of heating, and fade.

Yes, the best upgrade for performance is to increase the diameter, and caliper to a multi-pot caliper.

klattu

One advantage to brakes shoes is the first touch.
Much more initial friction.
Larger friction surface.
Of couse it all goes downhill from there.
NASCAR ran shoes for years after discs were on everything stock. (they were massive)
Rotors and pads were not able to produce instant heat.
Heat is transfer of energy from motion.

All much improved now.