Foxy
02-06-2006, 10:28 PM
Brake FAQ
This post is intended to be a summary of what I’ve learned about braking systems. I’m by no means an expert, and I know next to nothing about the specifics of the Grand Am’s braking system. This information is more general in nature, and should apply to any car.
If you notice anything wrong, please feel free to let me know, and I’ll correct this post. I’m a noob as far as cars go, so I really don’t mind being told I’m wrong. With that said, let’s dive in!
Brakes 101
If you don’t want to read my labored description, check out How Stuff Works (http://auto.howstuffworks.com/brake.htm). That’s a must-bookmark for anyone interested in a car.
The brake system in your car slows you down by converting the kinetic (motion) energy of your vehicle into heat. The amount of heat generated by the car is determined by the amount of energy in the system.
Kinetic Energy = ½ * mass * velocity^2
Therefore, if you double your speed, you quadruple the amount of heat generated. This is important to keep in mind.
The major heat sink in the system are the rotors (80% of the heat generated is dissipated through the rotors). However, the pads, fluids, wheels, hubs, bearings, and rubber gaskets in your braking system also absorb, and are susceptible to heat damage.
Imagine your brake system as a sink. When you brake, you turn on the faucet and begin to fill up the sink. Water drains out of the sink at a given rate through the drain at the bottom. If you brake harder or more frequently, you turn the faucet on more and more, so that more water (heat) enters the system. If you get too much water in the sink, the sink will overflow. If you get too much heat into the brakes before it can dissipate or drain the heat, you will get fade.
When you get brake fade, your pedal will become noticeably mushy, and braking distance will begin to increase. We’ll go into more detail about fade soon.
Your brakes do not stop your car. Your tires are what actually stops your car – the brakes only slow the rotation of the tires. The tires are what creates the friction patch between your car and the road. In order to actually shorten braking distance, you need wider, stickier tires. A good alignment might help keep the tires firmly squared to the road. When manufacturers quote stopping distance, this is a single stop from the given speed. Better brake systems are capable of maintaining that stopping distance over multiple stops (they are either larger sinks, or have larger drains, to go back to the sink/water analogy). If your current brakes can lock up the tires (activate ABS), you’re achieving about the minimum braking distance with your current tires.
Brake Rotors
#1 myth – brake rotors warp. No, they don’t!
Let me just quote from Stoptech:
Myth # 1 – BRAKE JUDDER AND VIBRATION IS CAUSED BY DISCS THAT HAVE BEEN WARPED FROM EXESSIVE HEAT.
The term "warped brake disc" has been in common use in motor racing for decades. When a driver reports a vibration under hard braking, inexperienced crews, after checking for (and not finding) cracks often attribute the vibration to "warped discs". They then measure the disc thickness in various places, find significant variation and the diagnosis is cast in stone.
When disc brakes for high performance cars arrived on the scene we began to hear of "warped brake discs" on road going cars, with the same analyses and diagnoses. Typically, the discs are resurfaced to cure the problem and, equally typically, after a relatively short time the roughness or vibration comes back. Brake roughness has caused a significant number of cars to be bought back by their manufacturers under the "lemon laws". This has been going on for decades now - and, like most things that we have cast in stone, the diagnoses are wrong.
With one qualifier, presuming that the hub and wheel flange are flat and in good condition and that the wheel bolts or hat mounting hardware is in good condition, installed correctly and tightened uniformly and in the correct order to the recommended torque specification, in more than 40 years of professional racing, including the Shelby/Ford GT 40s – one of the most intense brake development program in history - I have never seen a warped brake disc. I have seen lots of cracked discs, discs that had turned into shallow cones at operating temperature because they were mounted rigidly to their attachment bells or top hats, a few where the friction surface had collapsed in the area between straight radial interior vanes, and an untold number of discs with pad material unevenly deposited on the friction surfaces - sometimes visible and more often not.
In fact every case of "warped brake disc" that I have investigated, whether on a racing car or a street car, has turned out to be friction pad material transferred unevenly to the surface of the disc. This uneven deposition results in thickness variation (TV) or run-out due to hot spotting that occurred at elevated temperatures.
I've been told that Pontiac uses some really crappy rotors that are prone to actually warping. I'm not completely convinced, personally..
Brake Fluid
Your brakes are a hydraulic system. To oversimplify, when you press on the brakes, you press fluid through lines that actuate calipers that squeeze your rotors. Hydraulic systems work on the principle that the fluid is incompressible – when you make a motion on one side of the system, you get a similar motion on the other side.
So, brake fluid is the hydraulic fluid in the system. The fluids are designed to absorb heat and not lose their resistance to compressing. If you get fluid too hot, it will boil. When fluid boils, small bubbles of air form. Air is highly compressible, and the hydraulic system won’t be so.. hydraulic. Therefore, boiling fluid is bad – it makes your pedal feel mushy.
Fluids are classified into different types – DOT 3, DOT 4, DOT 5, and DOT 5.1 – depending on their boiling points. Boiling points are divided into Dry Boiling Points and Wet Boiling Points.
DOT 3, 4, and 5.1 are all compatible with each other, and have progressively higher boiling points. All of these fluids are highly corrosive to paint – don’t spill any on your car! DOT 5 is a silicon-based fluid and will not absorb water. It is also paint-friendly. However, silicon compresses easily. In addition, silicon fluid tends to froth when shaken, introducing air into the system. For this reason, DOT 5 fluid is not really recommended for street cars (it was developed for military / industrial applications where brake pedal feel is not critical). Show cars may want to use it, due to the fact that it won’t harm paint if spilled.
The Dry Boiling Point is the temperature where the fluid will boil when it is fresh and new. However, DOT 3, 4, and 5.1 fluids are hydroscopic – they absorb water. Water boils at 212 degrees F, and so, the absorption of any water will lower the fluid’s boiling point. All fluid will absorb water once it is out of the bottle. No brake system is completely impervious to water, and within a few weeks to a month, most fluids will be considered ‘wet.’ Therefore, Wet Boiling Point is the important feature to look at when purchasing fluid. Wet Boiling Point is the temperature that the fluid will boil at when it contains 3% water.
Also, be sure to flush your fluid once a year. Fluid will keep absorbing water past the 3% mark, and will progressively get worse. Also, if you do boil your fluid after a particularly spirited run, change it. Once the fluid boils, its boiling point is tremendously lowered, in addition to all of the little air bubbles now in the system.
Brake Fluid Boiling Points (determined by looking at the bottles, but I stole the list):
Fluid Brand || Wet Boiling Point || Dry Boiling Point
Castrol SRF || 518°F || 590°F
Earl's HyperTemp 421 || 421°F || 585°F
Motul 600 || 420°F || 593°F
AP-600 || 410°F || 572°F
Neosynthetic 610 || 421°F || 610°F
ATE-Super Blue || 392°F || 536°F
Valvoline || 333°F || 513°F
Castrol LMA || 311°F || 446°F
Earl's HyperTemp 300 || 300°F || 568°F
Ford HD || 290°F || 550°F
Wilwood 570 || 284°F || 570°F
PFC-Z rated || 284°F || 550°F
AP-550 || 284°F || 550°F
Castrol SRF looks like the best stuff, but you’ll pay for it. It’s something like $75/pint. Most of the other fluids are closer to $5-$10/pint. It’s mainly used by racing teams who can afford, and need the best. Motul 600 or Superblue is inexpensive, and available in many places (motorcycle shops tend to carry good brake fluid).
This post is intended to be a summary of what I’ve learned about braking systems. I’m by no means an expert, and I know next to nothing about the specifics of the Grand Am’s braking system. This information is more general in nature, and should apply to any car.
If you notice anything wrong, please feel free to let me know, and I’ll correct this post. I’m a noob as far as cars go, so I really don’t mind being told I’m wrong. With that said, let’s dive in!
Brakes 101
If you don’t want to read my labored description, check out How Stuff Works (http://auto.howstuffworks.com/brake.htm). That’s a must-bookmark for anyone interested in a car.
The brake system in your car slows you down by converting the kinetic (motion) energy of your vehicle into heat. The amount of heat generated by the car is determined by the amount of energy in the system.
Kinetic Energy = ½ * mass * velocity^2
Therefore, if you double your speed, you quadruple the amount of heat generated. This is important to keep in mind.
The major heat sink in the system are the rotors (80% of the heat generated is dissipated through the rotors). However, the pads, fluids, wheels, hubs, bearings, and rubber gaskets in your braking system also absorb, and are susceptible to heat damage.
Imagine your brake system as a sink. When you brake, you turn on the faucet and begin to fill up the sink. Water drains out of the sink at a given rate through the drain at the bottom. If you brake harder or more frequently, you turn the faucet on more and more, so that more water (heat) enters the system. If you get too much water in the sink, the sink will overflow. If you get too much heat into the brakes before it can dissipate or drain the heat, you will get fade.
When you get brake fade, your pedal will become noticeably mushy, and braking distance will begin to increase. We’ll go into more detail about fade soon.
Your brakes do not stop your car. Your tires are what actually stops your car – the brakes only slow the rotation of the tires. The tires are what creates the friction patch between your car and the road. In order to actually shorten braking distance, you need wider, stickier tires. A good alignment might help keep the tires firmly squared to the road. When manufacturers quote stopping distance, this is a single stop from the given speed. Better brake systems are capable of maintaining that stopping distance over multiple stops (they are either larger sinks, or have larger drains, to go back to the sink/water analogy). If your current brakes can lock up the tires (activate ABS), you’re achieving about the minimum braking distance with your current tires.
Brake Rotors
#1 myth – brake rotors warp. No, they don’t!
Let me just quote from Stoptech:
Myth # 1 – BRAKE JUDDER AND VIBRATION IS CAUSED BY DISCS THAT HAVE BEEN WARPED FROM EXESSIVE HEAT.
The term "warped brake disc" has been in common use in motor racing for decades. When a driver reports a vibration under hard braking, inexperienced crews, after checking for (and not finding) cracks often attribute the vibration to "warped discs". They then measure the disc thickness in various places, find significant variation and the diagnosis is cast in stone.
When disc brakes for high performance cars arrived on the scene we began to hear of "warped brake discs" on road going cars, with the same analyses and diagnoses. Typically, the discs are resurfaced to cure the problem and, equally typically, after a relatively short time the roughness or vibration comes back. Brake roughness has caused a significant number of cars to be bought back by their manufacturers under the "lemon laws". This has been going on for decades now - and, like most things that we have cast in stone, the diagnoses are wrong.
With one qualifier, presuming that the hub and wheel flange are flat and in good condition and that the wheel bolts or hat mounting hardware is in good condition, installed correctly and tightened uniformly and in the correct order to the recommended torque specification, in more than 40 years of professional racing, including the Shelby/Ford GT 40s – one of the most intense brake development program in history - I have never seen a warped brake disc. I have seen lots of cracked discs, discs that had turned into shallow cones at operating temperature because they were mounted rigidly to their attachment bells or top hats, a few where the friction surface had collapsed in the area between straight radial interior vanes, and an untold number of discs with pad material unevenly deposited on the friction surfaces - sometimes visible and more often not.
In fact every case of "warped brake disc" that I have investigated, whether on a racing car or a street car, has turned out to be friction pad material transferred unevenly to the surface of the disc. This uneven deposition results in thickness variation (TV) or run-out due to hot spotting that occurred at elevated temperatures.
I've been told that Pontiac uses some really crappy rotors that are prone to actually warping. I'm not completely convinced, personally..
Brake Fluid
Your brakes are a hydraulic system. To oversimplify, when you press on the brakes, you press fluid through lines that actuate calipers that squeeze your rotors. Hydraulic systems work on the principle that the fluid is incompressible – when you make a motion on one side of the system, you get a similar motion on the other side.
So, brake fluid is the hydraulic fluid in the system. The fluids are designed to absorb heat and not lose their resistance to compressing. If you get fluid too hot, it will boil. When fluid boils, small bubbles of air form. Air is highly compressible, and the hydraulic system won’t be so.. hydraulic. Therefore, boiling fluid is bad – it makes your pedal feel mushy.
Fluids are classified into different types – DOT 3, DOT 4, DOT 5, and DOT 5.1 – depending on their boiling points. Boiling points are divided into Dry Boiling Points and Wet Boiling Points.
DOT 3, 4, and 5.1 are all compatible with each other, and have progressively higher boiling points. All of these fluids are highly corrosive to paint – don’t spill any on your car! DOT 5 is a silicon-based fluid and will not absorb water. It is also paint-friendly. However, silicon compresses easily. In addition, silicon fluid tends to froth when shaken, introducing air into the system. For this reason, DOT 5 fluid is not really recommended for street cars (it was developed for military / industrial applications where brake pedal feel is not critical). Show cars may want to use it, due to the fact that it won’t harm paint if spilled.
The Dry Boiling Point is the temperature where the fluid will boil when it is fresh and new. However, DOT 3, 4, and 5.1 fluids are hydroscopic – they absorb water. Water boils at 212 degrees F, and so, the absorption of any water will lower the fluid’s boiling point. All fluid will absorb water once it is out of the bottle. No brake system is completely impervious to water, and within a few weeks to a month, most fluids will be considered ‘wet.’ Therefore, Wet Boiling Point is the important feature to look at when purchasing fluid. Wet Boiling Point is the temperature that the fluid will boil at when it contains 3% water.
Also, be sure to flush your fluid once a year. Fluid will keep absorbing water past the 3% mark, and will progressively get worse. Also, if you do boil your fluid after a particularly spirited run, change it. Once the fluid boils, its boiling point is tremendously lowered, in addition to all of the little air bubbles now in the system.
Brake Fluid Boiling Points (determined by looking at the bottles, but I stole the list):
Fluid Brand || Wet Boiling Point || Dry Boiling Point
Castrol SRF || 518°F || 590°F
Earl's HyperTemp 421 || 421°F || 585°F
Motul 600 || 420°F || 593°F
AP-600 || 410°F || 572°F
Neosynthetic 610 || 421°F || 610°F
ATE-Super Blue || 392°F || 536°F
Valvoline || 333°F || 513°F
Castrol LMA || 311°F || 446°F
Earl's HyperTemp 300 || 300°F || 568°F
Ford HD || 290°F || 550°F
Wilwood 570 || 284°F || 570°F
PFC-Z rated || 284°F || 550°F
AP-550 || 284°F || 550°F
Castrol SRF looks like the best stuff, but you’ll pay for it. It’s something like $75/pint. Most of the other fluids are closer to $5-$10/pint. It’s mainly used by racing teams who can afford, and need the best. Motul 600 or Superblue is inexpensive, and available in many places (motorcycle shops tend to carry good brake fluid).