doug in nc
Spectator
I wasn't sure if general tech, Wheels/Tires or Suspension was the appropriate section for this so I threw it in to general tech, move as required. Thought I'd share a bit of info I've already posted on other forums. Let me know if you have any questions or want to add something.
D
No matter what car you drive or how hard you apply the brakes you will, at some point in your life, experience a shimmy and pulsation feeling. When the car has ABS, most people think the pulsation is coming from the ABS. Other times, people chase suspension components but still can't fix it. In most cases, not all, the problem actually comes from a warped brake rotor. The shimmy felt in the steering wheel, brake pedal and car as a whole can be attributed to thickness variations in the brake rotors.
Most people can say they know if a rotor is warped just by looking at it. This is simply not true. You can tell if you have hot spots, cracking or POSSIBLY tell if the rotor is the source of a noise but without measuring the thickness of the rotor in multiple spots or cutting it on a lathe, you'll never be able to detect with the human eye the variations that cause a pulsation. Hopefully, by the time you're done reading this post you'll be able to understand fact from fiction when it comes to your brakes. The test subject for this article was my old 99 Mitsubishi Eclipse that had warped rotors and so I took a few extra steps here to gather up enough pictures for your enjoyment.
Though my old eclipse was non-turbo I upgraded the front pads and rotors to GSX brakes. The larger front rotors were made by Powerslot. They've got slots cut in them that help cool the rotor and vent gas build-up between the pad and rotor surface, according to many manufacturers' advertisements. Additional attention is needed when cutting slotted/dimpled/drilled rotors to prevent cutting too much in a single swipe which can damage the lathe. Also, rotor thickness plays a large factor in the ability to shed heat so cutting too much can cause your rotors to be too thin and be a hazard to drive. Ultimately, the best repair for warped rotors is new ones but when you look at the cost for new performance rotors, you may roll the dice and just cut the ones on the car.
First you see the rotor on the car in picture 1.
I've marked the rotor with an "R" so that I know which side it goes back on. The rotors have to go back on a certain way in order for them to cool and vent gases. If the slots are going the wrong way then the gases and heat are directed towards the center of the rotor. When properly installed all of that is directed out towards the wheel where there is more air and the gases can escape. I've also marked the rotor to the hub so that it goes back on in the same spot it came off at. Much like the imbalance felt when you remove a tire from a rim and reinstall it in a different position, the rotor warps/wears to the hub it came from. Re-installation in a different position MAY lead to a warpage-like feeling that previously was not felt.
There are two types of brake lathes out there. One cuts a rotor while it's removed from the car. The other type of brake lathe cuts the rotor while it's still attached to the hub. What the on-car lathe does is matches up the rotor and the hub as a near perfect fit. It's kinda like balancing a tire on the car. It's just more precise to do things on the car in their own environment than a universal off-car machine. The important part here is that once a rotor is cut on the car it CANNOT be removed and put back on in a whatever position you want. All the lug nut holes must line up with the lug nut studs they were cut next to. If you remove them and put them back on in a different way then clicking, vibrations, knocking or other sorts of noises will occur when braking. In some cases the variances are so great that the noise will show up even without hitting the brakes.
The pictures 2 and 3 show the rotor on a brake lathe.
This is a component designed to remove metal evenly from both sides of the rotor. The rotor is chucked up on to an arbor which spins around the same as it would on a car. The bits cut the metal off of the rotor as it's spinning. The idea is that you remove as little as possible from each side but still have it completely flat/true/straight. The bits have knobs at the opposite end (closest to me taking the picture) that have fractions of an inch measurements on them to help determine how much you're cutting off. As the rotor spins, with the cutting bits touching the rotor, the bits are on a gear drive that pulls the bits towards the outer portion of the rotor. As such the metal is shaved off as the rotor spins and the bits more outward.
Alot of brake noises are actually caused by vibrations. Metal in the brake pads themselves is touching the rotors causing a squeal. That squeal is a vibration occurring at such a frequency that the human ear can detect it. The brake lathe is also subject to vibrations as the rotor is being cut. To prevent this we wrap basically a rubber band around the rotor to absorb vibrations. Vibrations while cutting turn in to grooves in the rotor. Sometimes once grooves get cut in to a rotor, they cannot be removed. If you get a rotor back from a machine shop or repair shop that looks like an old-school record, you can bet it will produce noises, usually a sound similar to metal-to-metal brakes since it's a really grainy cut on the rotor.
Picture 4 shows my first cut on the rotor.
As you can see there's alot of metal shavings all over the machine and in the catch pan. BUT what is more important for you to see is the shiny spot compared to the dull/grayish area. The shiny section is uncut rotor. As you can see the section of the rotor that has been cut is not even. There are high spots and low spots in the surface of the metal. These differences in thickness and shape are what cause the pulsation we feel in the pedal as brakes are applied. Pictures 5 and 6 are prime examples as to the differences in thickness.
If you look at picture 5 shown here:
you will see that I have marked the rotor with a 1, 2, 3, and 4. I marked the rotor the same on the opposite side as well. I'll refer to each number as a "position" for ease of interpreting. Notice how in position 2 in picture 5 shows an area that has been cut. But in picture 6 shown here:
it is uncut. This is an example of how warped these rotors are. Positions 1, 2, and 3 are cut on one side and completely uncut on the other.
Pictures 7-10 show the rotor a little bit further in the cutting process. Pictures 7 and 10 show the outside of the rotor. We've got alot more area that shows as being cut but as you can tell the metal still is not even nor fully cut even after a couple of swipes. Pictures 8 and 9 show the opposite side as being in the same condition.
The last two pictures above show the rotor almost completely done with only a small section remaining uncut. The finished product is a nice, even finish on the rotor on both sides. This gives the brake pads an even surface to contact with ensuring that 100% of the pad surface comes in contact with the rotor providing as much stopping ability as possible.
As a finishing process we do one or two more steps. First is to clean the rotor with brake cleaner to remove the machining dust. This dust can act like graphite does. Sure, it's a dry metal dust but because it's so fine it can actually act as a lubricant. Your new pads will be imbedded with dust and performance will suffer. The next step sometimes done is to take a die grinder with an abrasive disc and score up the surface. This is done as the rotor is spinning and is done in such a manor so as to help remove a finish that looks like a pinwheel starting from the center of the rotor and working it's way outward. Both of these finishing steps are done to reduce noise, decrease brake bedding time and keep the new pads clean.
D
No matter what car you drive or how hard you apply the brakes you will, at some point in your life, experience a shimmy and pulsation feeling. When the car has ABS, most people think the pulsation is coming from the ABS. Other times, people chase suspension components but still can't fix it. In most cases, not all, the problem actually comes from a warped brake rotor. The shimmy felt in the steering wheel, brake pedal and car as a whole can be attributed to thickness variations in the brake rotors.
Most people can say they know if a rotor is warped just by looking at it. This is simply not true. You can tell if you have hot spots, cracking or POSSIBLY tell if the rotor is the source of a noise but without measuring the thickness of the rotor in multiple spots or cutting it on a lathe, you'll never be able to detect with the human eye the variations that cause a pulsation. Hopefully, by the time you're done reading this post you'll be able to understand fact from fiction when it comes to your brakes. The test subject for this article was my old 99 Mitsubishi Eclipse that had warped rotors and so I took a few extra steps here to gather up enough pictures for your enjoyment.
Though my old eclipse was non-turbo I upgraded the front pads and rotors to GSX brakes. The larger front rotors were made by Powerslot. They've got slots cut in them that help cool the rotor and vent gas build-up between the pad and rotor surface, according to many manufacturers' advertisements. Additional attention is needed when cutting slotted/dimpled/drilled rotors to prevent cutting too much in a single swipe which can damage the lathe. Also, rotor thickness plays a large factor in the ability to shed heat so cutting too much can cause your rotors to be too thin and be a hazard to drive. Ultimately, the best repair for warped rotors is new ones but when you look at the cost for new performance rotors, you may roll the dice and just cut the ones on the car.
First you see the rotor on the car in picture 1.
I've marked the rotor with an "R" so that I know which side it goes back on. The rotors have to go back on a certain way in order for them to cool and vent gases. If the slots are going the wrong way then the gases and heat are directed towards the center of the rotor. When properly installed all of that is directed out towards the wheel where there is more air and the gases can escape. I've also marked the rotor to the hub so that it goes back on in the same spot it came off at. Much like the imbalance felt when you remove a tire from a rim and reinstall it in a different position, the rotor warps/wears to the hub it came from. Re-installation in a different position MAY lead to a warpage-like feeling that previously was not felt.
There are two types of brake lathes out there. One cuts a rotor while it's removed from the car. The other type of brake lathe cuts the rotor while it's still attached to the hub. What the on-car lathe does is matches up the rotor and the hub as a near perfect fit. It's kinda like balancing a tire on the car. It's just more precise to do things on the car in their own environment than a universal off-car machine. The important part here is that once a rotor is cut on the car it CANNOT be removed and put back on in a whatever position you want. All the lug nut holes must line up with the lug nut studs they were cut next to. If you remove them and put them back on in a different way then clicking, vibrations, knocking or other sorts of noises will occur when braking. In some cases the variances are so great that the noise will show up even without hitting the brakes.
The pictures 2 and 3 show the rotor on a brake lathe.
This is a component designed to remove metal evenly from both sides of the rotor. The rotor is chucked up on to an arbor which spins around the same as it would on a car. The bits cut the metal off of the rotor as it's spinning. The idea is that you remove as little as possible from each side but still have it completely flat/true/straight. The bits have knobs at the opposite end (closest to me taking the picture) that have fractions of an inch measurements on them to help determine how much you're cutting off. As the rotor spins, with the cutting bits touching the rotor, the bits are on a gear drive that pulls the bits towards the outer portion of the rotor. As such the metal is shaved off as the rotor spins and the bits more outward.
Alot of brake noises are actually caused by vibrations. Metal in the brake pads themselves is touching the rotors causing a squeal. That squeal is a vibration occurring at such a frequency that the human ear can detect it. The brake lathe is also subject to vibrations as the rotor is being cut. To prevent this we wrap basically a rubber band around the rotor to absorb vibrations. Vibrations while cutting turn in to grooves in the rotor. Sometimes once grooves get cut in to a rotor, they cannot be removed. If you get a rotor back from a machine shop or repair shop that looks like an old-school record, you can bet it will produce noises, usually a sound similar to metal-to-metal brakes since it's a really grainy cut on the rotor.
Picture 4 shows my first cut on the rotor.
As you can see there's alot of metal shavings all over the machine and in the catch pan. BUT what is more important for you to see is the shiny spot compared to the dull/grayish area. The shiny section is uncut rotor. As you can see the section of the rotor that has been cut is not even. There are high spots and low spots in the surface of the metal. These differences in thickness and shape are what cause the pulsation we feel in the pedal as brakes are applied. Pictures 5 and 6 are prime examples as to the differences in thickness.
If you look at picture 5 shown here:
you will see that I have marked the rotor with a 1, 2, 3, and 4. I marked the rotor the same on the opposite side as well. I'll refer to each number as a "position" for ease of interpreting. Notice how in position 2 in picture 5 shows an area that has been cut. But in picture 6 shown here:
it is uncut. This is an example of how warped these rotors are. Positions 1, 2, and 3 are cut on one side and completely uncut on the other.
Pictures 7-10 show the rotor a little bit further in the cutting process. Pictures 7 and 10 show the outside of the rotor. We've got alot more area that shows as being cut but as you can tell the metal still is not even nor fully cut even after a couple of swipes. Pictures 8 and 9 show the opposite side as being in the same condition.
The last two pictures above show the rotor almost completely done with only a small section remaining uncut. The finished product is a nice, even finish on the rotor on both sides. This gives the brake pads an even surface to contact with ensuring that 100% of the pad surface comes in contact with the rotor providing as much stopping ability as possible.
As a finishing process we do one or two more steps. First is to clean the rotor with brake cleaner to remove the machining dust. This dust can act like graphite does. Sure, it's a dry metal dust but because it's so fine it can actually act as a lubricant. Your new pads will be imbedded with dust and performance will suffer. The next step sometimes done is to take a die grinder with an abrasive disc and score up the surface. This is done as the rotor is spinning and is done in such a manor so as to help remove a finish that looks like a pinwheel starting from the center of the rotor and working it's way outward. Both of these finishing steps are done to reduce noise, decrease brake bedding time and keep the new pads clean.
