Wednesday, April 6, 2011

Brakes - Part One

This topic covers a whole range of items, but today I’ll just cover changing brake pads on disc brakes (I’ll cover drum brakes later on). Disc brakes use a pair of pads that clamp against the flat rotor or disc, while drum brakes use brake shoes that expand against the inside of a cylindrical drum. These brake types are both hydraulic systems designed to convert the forward momentum of a moving vehicle into heat and slow the vehicle.

There are two types of disc brake system in use today. They can be identified by their caliper piston position. The floating caliper disc brake system can be identified by caliper piston(s) located in only one side of the caliper assembly. When the brakes are applied by the driver, the inside pad is forced against the rotor. As the force increases, the inside pad pushes against the rotor and forces the caliper to slide on its slide pins and pull the outside pad against the rotor. This is the most common caliper design used today.

The fixed caliper disc brake system is identified by its multiple pistons, with equal number of pistons on each side of the caliper. In this system, as the brakes are applied, the force is applied equally on both sides of the rotor surface. This clamping force is what stops the vehicle.

Replacing Your Brake Pads

What You Are Going To Need:
• lug wrench
• c-clamp
• open end or adjustable wrench (depending on your car)
• Allen wrenches (depending on your car)
• hammer
• small bungee cord
• a face mask to guard against inhaling brake dust

Preparation
Be sure you've got everything ready to go before you remove your old brake pads. Most important, be sure safety is at the front of your mind. You'll be taking the wheel off so be sure you have your car jacked up and resting on jack stands. Go ahead and start loosening (a turn or two) the lug nuts while the vehicle is still on the ground (it’s easier and safer that way). Remember – lefty loosens and righty tightens! Keep in mind that if your brakes are working properly, the front brakes will wear out first as they do most of the stopping.

You slightly loosen the lug nuts while the car was still on the ground, so they should be pretty easy to remove. I like to remove them from the bottom up, leaving the top lug nut to be removed last. This keeps the wheel in one place while you remove the rest of them and makes it easier to safely catch the wheel once you remove the last nut. You can't replace brake pads with the wheel on!

The Caliper
On most cars, the next step is to remove the brake caliper so the brake pads will slide out through the top. On a few cars the pads will come out without removing the caliper, but not many. You'll see the brake caliper in the 12 o'clock position just above the lug bolts, riding atop that shiny brake disc.


On the back of the caliper you'll find a bolt on either side. It will either be a hex bolt of an Allen bolt. Remove these two bolts and put them aside.

Hold the caliper from the top and pull upward, wiggling it around to loosen it up. If it's stubborn, give it a few taps (taps, not sledge hammer whacks) upward to loosen it a bit. Pull it up and slightly away, being sure not to put any stress on the brake line (that black hose that's still connected).


If there is a place to safely set the caliper back there, do it. If not, you'll need to take your bungee cord and hang the caliper from something, the giant coil spring staring at you is a good spot. Don't let the caliper hang by the brake line, it can cause damage and lead to brake failure!

Remove the Old Brake Pads
Before you pull out the old brake pads, take a second to observe how everything is in installed. If there are little metal clips around the brake pads, note how they are in there so you can get it right when you put things back together. Better yet, take a digital picture of the whole assembly.

With the caliper out of the way, the brake pads should slide right out. I say should because in a new car they probably would. Since our cars are not always new, you may need to coax them out with a litte tap of the hammer to loosen them up. If your car has little metal tabs holding onto the brake pads, put them to the side becase you'll need them in a minute. Put the new pads in the slots with any metal clips you removed.


While you’re there, inspect your brake discs for any gouges, scratches, oil or other foreign matter. You may have to either get the disc turned or replaced if you have deep gouges.

Go ahead and slide the new pads into place now, making sure you don't forget any of the little retaining clips you removed earlier.

Compress the Brake Piston
As your brake pads wear out, the caliper adjusts itself so that you will have strong brakes throughout the life of the pads. If you look on the inside of the caliper you'll see a round piston coming out. This is what pushes on the brake pads from the back. Problem is, it's adjusted itself to match your worn out pads. Trying to get it over the new pads is like parking a dump truck in New York City. You can do it, but the damage level will be high. Instead of destroying your new pads, you'll push the piston back to the starting point.


Take the c-clamp and place the end with the screw on it against the piston with the other end of the clamp around on the back of the caliper assembly. Now slowly tighten the clamp until the piston has moved far enough in that you can easily plop the caliper assembly over the new pads.

Re-Install the Brake Caliper
With the piston compressed, you should be able to easily slide the caliper assembly over the new pads. Once you have it on there, replace the bolts you removed and tighten them snugly. Press the brake pedal a few times to make sure you have solid brake pressure. The first pump or two will be soft as the piston finds its new starting point on the back of the pad.

Put your wheel back on, being sure to tighten all of the lug bolts. Remove your vehicle from the jack stands and jack. Now double-check your lug bolts just to be sure they tight and secure.


Now find a place where you can back-up in a straight line safely. Get your speed up to 5 – 10 mph and slowly apply the emergency brake. This should insure all brakes are applying a like amount of stopping force so the vehicle will not pull to the right/left when stopping while going forward.

Good luck and will see ya next time!

10 comments:

  1. i said allways the same think, but is just true.. very usefull post.. hahaha..

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  2. I just got my car repaired because of the breaks, its really useful info here but in all honesty im kinda afraid i screw up and then having to take the care to the shop only to get raped by the bill that will be double the price had i taken it there in the first place.

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  3. nice read, thanks for the info!

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  4. thanks for the info! i hope i won't need to change my brakes. :)

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  5. Nice blog BRO!!!

    fallowing and $upporting

    http://darkbogdanel.blogspot.com

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  6. every mechanic should read this!! do you study something at university related to this or what? thank you for sharing

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  7. I think this sounds difficult. You provide good instructions, I'd just hate to mess up the brakes. Digital pictures would definitely be a must!

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  8. You sure know a lot about fixing cars...if something happens to my breaks, I'll know what to do now!

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