I've worked since 2001 in a brake specialist shop. All my mechanic friends call me a "brake nerd". There's a lot of good info on this site about how to work on our brakes but i just wanted to talk a bit about brake systems overall and common things they DIYer doesn't know to look for.
First I'm going to spend a minute talking about rotors and pulsations. I think this area needs a brighter light shed on it than what I've found while browsing.
Rotor Basics
There are a few important specs a rotor needs to meet in order to be "good"
Minimum Thickness/Discard Spec : your disk must be thicker that this
TIR : Total installed runout. This is the total stacked runout in your wheel end assembly
some vehicles also have a "machine to" spec but not hondas so I won't talk about it again.
What is a "warped rotor"?
The term warped doesn't technically mean anything. What most of us picture as a warped rotor is called lateral runout. When a rotor has excessive runout it will push the caliper back and forth on the guide-pins as it passes through the caliper assembly. Assuming the disk is uniform in thickness and the pads and pins are moving freely you will not feel this when you brake (the piston is NOT being pushed back into the caliper bore) but you might hear a cyclical squeaking or chirping sound.
So what causes pulsations?
When you feel that shaking, usually first noticable at high speeds, what your feeling is disk thickness variation (DTV). In this case your disk is not the same thickness all the way around and as a result the piston is getting pushed back into the caliper as the thicker part of the rotor passed through and pushed back out again by your braking as the thinner part passes.
Where did the DTV come from?
Lateral runout leads to DTV. Imagine the disk spinning, a pad on either side, excessive runout in the disk. As the high side on the disk passes the outer pad it pushes that pad out, which pulls the whole assembly outward. On each revolution the outer pad pushes against the same spot on the outside plate of the rotor. The same thing is happening 180 degrees around on the inside. Over a period of time this will lead to uneven wear and uneven distribution of pad material on the rotor. Congratulation we have achieved Disk Thickness Variation
Thats neat and all but the solution is the same so whats it matter?
When you replace a rotor (especially on a HOR car like most of ours still are) its important that the TIR (total installed runout) falls within spec. Most of us don't have runout gages and I would't suggest going out to buy one unless you plan on being a full time brake nerd like me. What I would suggest, and what I always do on a HOR, is use a knuckle mounted on the car brake lathe to achieve perfect 0 TIR. I know most people don't have one (even most shops don't) but its worth the legwork to find someone in your area who can do it for you and its usually not very expensive. If your taking my advice here it may have already dawned on you that if your going to have the rotor machined on the car after you change it you may not need to change it at all. All but the most severely "warped" rotors can be machined true again in as little as .010" - .020". I wouldn't recommend getting too close to the discard spec, but if your measuring .040" or more above discard I would machine the existing rotor.
If your ROH just be sure that the mounting surfaces are clean, and if you remove your rotor for servicing be sure to index it to the hub and install in the same position it was removed from.
The next most common source of lateral runout is uneven wheel torque. Always hand torque your wheels to 80 ft/lbs in a star pattern (specs vary but for us its 80) and make sure any shop that touches your wheels does the same.
Now a small bit on pads
Pads are by far the most boring piece of the brake puzzle. When they are close to worn out change them.
They come in a variety of compositions and price ranges. You get what you pay for here so bear that in mind when choosing your pads, cheaper pads tend to be more prone to noise issues as well as excessive wear to your rotors.
The pads are your best indicator of the health of your caliper, so with that in mind lets move on to calipers.
Calipers
When your working on your brakes look for abnormal wear patterns in the pads. If everything is working normally all four pads in an axle set should wear very close to the same. If your inboard pads are worn further than your outer pads then your caliper piston is not retracting. If the outer pads are worn further its a problem with the guide pins or outer pad sticking in the hardware. You can buy rebuild kits that include the seal and dust boot and rebuild them yourself or just buy some remans but I wouldn't ignore it, as it leads to reduced friction life, noise issues and if you combine this with that excessive TIR we talked about earlier it will exacerbate that situation obviously.
Also look at the dust boot around the piston and make sure its not torn or melted, lift it up a little and make sure its clean and dry inside. If theres brake fluid in there its leaking, rebuild or replace.
As far as the caliper hardware goes, I recommend replacing the hardware clips (shiny pieces that fin in the bracket) every time you change the pads. These parts can be bought in a kit very cheaply and also come packaged with several different brand pads and pretty much any reman caliper. Pull the guide pins out and clean and relube them with a silicone based paste.
Fluid
Keep it clean! Dirty brake fluid, especially when left for long periods of time in a system, causes all kinds of problems with hydraulic components.
NEVER EVER EVER use anything other than dot3 or dot4 brake fluid in a street car. Racing fluid is not hygroscopic and will allow water to pool in your brake system causing corrosion.
ANYTHING petroleum based will RUIN EVERY HYDRAULIC COMPONENT in your brake system.
Bleeding
The best way to do this is with a pressure bleeder. I realize that most people don't have one and will probably just have their buddy push the pedal while they open and close the bleeders. When you do it that way there's a few things you should understand about how a master cylinder is made to avoid damage.
The primary seals in your master are situated at the front edge of an aluminum piston. There is a steel screw called a piston stop block protruding into the bore that is there to prevent the piston traveling so far down the bore that it passes the outlet ports thereby releasing all hydraulic pressure. Understand that your piston will only travel that far down in the event of a hydraulic failure (your creating one by opening the bleeder valve). The important thing here is to be gentle when depressing the brake pedal and don't let it go all the way down until it bottoms out. If that aluminum piston and rubber seal slam that steel screw it will do damage, its just a question of how much damage was done. Our cars have enough master cylinder issues without us damaging them while bleeding our brakes.
Drum brakes
Drum brakes work a little differently than disks but your still using hydraulic pressure to force a stationary friction material into a spinning metal surface to make a stop (converting kinetic energy into heat energy via friction). Inspect the wheel cylinders by lifting the dust boots on the ends up and looking inside, if its clean and dry its fine, if its wet or corroded replace it. I suggest changing the springs every time you do the shoes. Our shoes usually last a long time and those springs have been back there stretching and releasing, heating and cooling the whole time. The spring kits aren't much so don't cheap out. Use you parking brake regularly to maintain adjustment in the rear brakes.
I hope this is helpful to anyone who reads it, I didn't really intend to have such a long write-up when I started this but one thought leads to another I suppose. Feel free to ask for clarification if you don't get what I mean or anything else brake related you might need help with.
First I'm going to spend a minute talking about rotors and pulsations. I think this area needs a brighter light shed on it than what I've found while browsing.
Rotor Basics
There are a few important specs a rotor needs to meet in order to be "good"
Minimum Thickness/Discard Spec : your disk must be thicker that this
TIR : Total installed runout. This is the total stacked runout in your wheel end assembly
some vehicles also have a "machine to" spec but not hondas so I won't talk about it again.
What is a "warped rotor"?
The term warped doesn't technically mean anything. What most of us picture as a warped rotor is called lateral runout. When a rotor has excessive runout it will push the caliper back and forth on the guide-pins as it passes through the caliper assembly. Assuming the disk is uniform in thickness and the pads and pins are moving freely you will not feel this when you brake (the piston is NOT being pushed back into the caliper bore) but you might hear a cyclical squeaking or chirping sound.
So what causes pulsations?
When you feel that shaking, usually first noticable at high speeds, what your feeling is disk thickness variation (DTV). In this case your disk is not the same thickness all the way around and as a result the piston is getting pushed back into the caliper as the thicker part of the rotor passed through and pushed back out again by your braking as the thinner part passes.
Where did the DTV come from?
Lateral runout leads to DTV. Imagine the disk spinning, a pad on either side, excessive runout in the disk. As the high side on the disk passes the outer pad it pushes that pad out, which pulls the whole assembly outward. On each revolution the outer pad pushes against the same spot on the outside plate of the rotor. The same thing is happening 180 degrees around on the inside. Over a period of time this will lead to uneven wear and uneven distribution of pad material on the rotor. Congratulation we have achieved Disk Thickness Variation
Thats neat and all but the solution is the same so whats it matter?
When you replace a rotor (especially on a HOR car like most of ours still are) its important that the TIR (total installed runout) falls within spec. Most of us don't have runout gages and I would't suggest going out to buy one unless you plan on being a full time brake nerd like me. What I would suggest, and what I always do on a HOR, is use a knuckle mounted on the car brake lathe to achieve perfect 0 TIR. I know most people don't have one (even most shops don't) but its worth the legwork to find someone in your area who can do it for you and its usually not very expensive. If your taking my advice here it may have already dawned on you that if your going to have the rotor machined on the car after you change it you may not need to change it at all. All but the most severely "warped" rotors can be machined true again in as little as .010" - .020". I wouldn't recommend getting too close to the discard spec, but if your measuring .040" or more above discard I would machine the existing rotor.
If your ROH just be sure that the mounting surfaces are clean, and if you remove your rotor for servicing be sure to index it to the hub and install in the same position it was removed from.
The next most common source of lateral runout is uneven wheel torque. Always hand torque your wheels to 80 ft/lbs in a star pattern (specs vary but for us its 80) and make sure any shop that touches your wheels does the same.
Now a small bit on pads
Pads are by far the most boring piece of the brake puzzle. When they are close to worn out change them.
They come in a variety of compositions and price ranges. You get what you pay for here so bear that in mind when choosing your pads, cheaper pads tend to be more prone to noise issues as well as excessive wear to your rotors.
The pads are your best indicator of the health of your caliper, so with that in mind lets move on to calipers.
Calipers
When your working on your brakes look for abnormal wear patterns in the pads. If everything is working normally all four pads in an axle set should wear very close to the same. If your inboard pads are worn further than your outer pads then your caliper piston is not retracting. If the outer pads are worn further its a problem with the guide pins or outer pad sticking in the hardware. You can buy rebuild kits that include the seal and dust boot and rebuild them yourself or just buy some remans but I wouldn't ignore it, as it leads to reduced friction life, noise issues and if you combine this with that excessive TIR we talked about earlier it will exacerbate that situation obviously.
Also look at the dust boot around the piston and make sure its not torn or melted, lift it up a little and make sure its clean and dry inside. If theres brake fluid in there its leaking, rebuild or replace.
As far as the caliper hardware goes, I recommend replacing the hardware clips (shiny pieces that fin in the bracket) every time you change the pads. These parts can be bought in a kit very cheaply and also come packaged with several different brand pads and pretty much any reman caliper. Pull the guide pins out and clean and relube them with a silicone based paste.
Fluid
Keep it clean! Dirty brake fluid, especially when left for long periods of time in a system, causes all kinds of problems with hydraulic components.
NEVER EVER EVER use anything other than dot3 or dot4 brake fluid in a street car. Racing fluid is not hygroscopic and will allow water to pool in your brake system causing corrosion.
ANYTHING petroleum based will RUIN EVERY HYDRAULIC COMPONENT in your brake system.
Bleeding
The best way to do this is with a pressure bleeder. I realize that most people don't have one and will probably just have their buddy push the pedal while they open and close the bleeders. When you do it that way there's a few things you should understand about how a master cylinder is made to avoid damage.
The primary seals in your master are situated at the front edge of an aluminum piston. There is a steel screw called a piston stop block protruding into the bore that is there to prevent the piston traveling so far down the bore that it passes the outlet ports thereby releasing all hydraulic pressure. Understand that your piston will only travel that far down in the event of a hydraulic failure (your creating one by opening the bleeder valve). The important thing here is to be gentle when depressing the brake pedal and don't let it go all the way down until it bottoms out. If that aluminum piston and rubber seal slam that steel screw it will do damage, its just a question of how much damage was done. Our cars have enough master cylinder issues without us damaging them while bleeding our brakes.
Drum brakes
Drum brakes work a little differently than disks but your still using hydraulic pressure to force a stationary friction material into a spinning metal surface to make a stop (converting kinetic energy into heat energy via friction). Inspect the wheel cylinders by lifting the dust boots on the ends up and looking inside, if its clean and dry its fine, if its wet or corroded replace it. I suggest changing the springs every time you do the shoes. Our shoes usually last a long time and those springs have been back there stretching and releasing, heating and cooling the whole time. The spring kits aren't much so don't cheap out. Use you parking brake regularly to maintain adjustment in the rear brakes.
I hope this is helpful to anyone who reads it, I didn't really intend to have such a long write-up when I started this but one thought leads to another I suppose. Feel free to ask for clarification if you don't get what I mean or anything else brake related you might need help with.
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