Need a serious brake guy
Thanks Ken. It still shocks me how often you hear this from ASE mechanics and service advisors. But hey, the Earth used to be flat..... Right? 
Elder User
Joined: Nov 2004
Posts: 759
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From: Ventura ,ca. (near L.A.)
If my rotors didn't warp then what is the explanation for the pulsation happening and having the rotors turned 3 times in 25k wen i didn't torque them and then when i did start torquing them it doesn't have a problem with pulsation anymore. As far as heat range goes im probably harder on the brakes now then when i bought the truck since 50% of my driving is in the city when before it was about 75%.
Fleet Mechanic
Joined: Dec 2003
Posts: 1,436
Likes: 117
From: Virginia
There is always going to be someone to challenge something different when they have been told the opposite all their life. The most likely explanation for your situation is a little bit coincidence added with the removal of all those surface layers.
If you read the articles and think about how the deposits + excess heat penetrate the face of the rotor. This causes the metal to take on a very hard and brittle form of iron called cementite.
QUOTE:
"It gets worse. Cast iron is an alloy of iron and silicon in solution interspersed with particles of carbon. At elevated temperatures, inclusions of carbides begin to form in the matrix. In the case of the brake disk, any uneven deposits - standing proud of the disc surface - become hotter than the surrounding metal. Every time that the leading edge of one of the deposits rotates into contact with the pad, the local temperature increases. When this local temperature reaches around 1200 or 1300 degrees F. the cast iron under the deposit begins to transform into cementite (an iron carbide in which three atoms of iron combine with one atom of carbon). Cementite is very hard, very abrasive and is a poor heat sink. If severe use continues the system will enter a self-defeating spiral - the amount and depth of the cementite increases with increasing temperature and so does the brake roughness. Drat!"
The absolute crucial part to avoiding this problem is the bedding in of the pads to the rotor surface, not torque settings. This is not to say torque settings are irrelevant. The real danger to over or under torquing bolts is the possibility of it shearing off while driving.
If you read the instructions that come with any quality set of pads they will have a section that recommends how to properly bed the pads in. Failure to do so can result in this "pulsing brake" problem or decreased brake life.
If you read the articles and think about how the deposits + excess heat penetrate the face of the rotor. This causes the metal to take on a very hard and brittle form of iron called cementite.
QUOTE:
"It gets worse. Cast iron is an alloy of iron and silicon in solution interspersed with particles of carbon. At elevated temperatures, inclusions of carbides begin to form in the matrix. In the case of the brake disk, any uneven deposits - standing proud of the disc surface - become hotter than the surrounding metal. Every time that the leading edge of one of the deposits rotates into contact with the pad, the local temperature increases. When this local temperature reaches around 1200 or 1300 degrees F. the cast iron under the deposit begins to transform into cementite (an iron carbide in which three atoms of iron combine with one atom of carbon). Cementite is very hard, very abrasive and is a poor heat sink. If severe use continues the system will enter a self-defeating spiral - the amount and depth of the cementite increases with increasing temperature and so does the brake roughness. Drat!"
The absolute crucial part to avoiding this problem is the bedding in of the pads to the rotor surface, not torque settings. This is not to say torque settings are irrelevant. The real danger to over or under torquing bolts is the possibility of it shearing off while driving.
If you read the instructions that come with any quality set of pads they will have a section that recommends how to properly bed the pads in. Failure to do so can result in this "pulsing brake" problem or decreased brake life.
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Wacenturion
Brakes, Steering, Suspension, Tires, & Wheels
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Jun 27, 2013 07:01 AM
