Compressing Caliper for Brake Pads

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Learn how to compress the caliper when changing the car front brake pads with expert automotive tips in this free online car maintenance and repair video clip.

Part of the Video Series: How to Replace Front Brake Pads
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Video Transcript

MARK BLOCKER: Okay. In this segment, we're going to cover compressing the caliper. And what I'm referring to is the caliper sitting under--as your brake pads are wearing down, this caliper piston has to keep traveling out further and further. And when you let off the brake, the caliper doesn't--the piston doesn't come back in. It stays roughly right there. It just doesn't have pressure against it. And that ensures that the brake pads are right there tight so you get a good swift, clean braking action every time you apply the brakes. But as the brake pads wear down and the caliper extends--the piston extends further and further outward, in order to have room for the new pads, we need to compress this piston back into the caliper. I like to use just a large pair of pliers. You can use a C-clamp; that works real well. A good way to compress it is if you take one of the old pads--and we'll just lay it in there across the piston. And that gives a large surface to push against and it also helps ensure that the pressure we're using to push it is applied evenly across the piston so the piston doesn't want to bind, they want to compress it back in. And essentially, what we're going to do when we compress this in, we're pushing the fluid back through the brake line and back into the master cylinder. Now, a lot of times, when you have your car service and people will be checking various items, they'll check that brake fluid and they'll say, "Oh, it's a little bit low." They'll add brake fluid. If that's the case, and right now, your brake master cylinder reservoir is full. When you compress this, that brake fluid is going to come out of the top of the vent--on the breather cap for the master cylinder and you'll see it dripping down on the floor. I'm making you aware of this so if you see this happening, you'll know why it happened and understand. And it's just 'cause of the fact that somebody's topped off your master cylinder. If your master cylinder level is low but not below the add line, never add break fluid. That's usually just an indication that your brake pads are getting worn and the pistons have travelled outward and your brake fluid isn't necessarily leaking, it's being held down here in the caliper right now instead of the reservoir. So, I'll just get my pliers set up to adjust for a--large enough to get around the caliper itself in the back of the--from the back of the caliper to the front where the piston is and have enough room for a brake pad. Just lay the old brake pad in there, and then I'm just going to apply a gentle, even force and watch the piston travel backwards. I'm compressing it into the caliper. You want to just squeeze it until it goes all the way down and it'll stop there and you want to make sure it goes all the way in. And then remove your brake pad and you'll inspect to make sure that that rubber seal that came out. That was a dust seal that kept dirt and contaminants away from the piston, is all seated in there correctly and nothing's ripped or torn. You might want to take a little bit of your brake clean and a rag. And this time, you'd wipe out any excess dirt or dust. Check and make sure that you're caliper mounting pivot slides freely. This is where the bolt is and this is the pivot point here. The pivot point doesn't move. It's got a large boot on it. You want to inspect it. See it's not torn or contains grease inside. Now, we've got the caliper compressed. We know all the caliper functions are working correctly. We'll go ahead and set it aside. Our next segment, we're going to cover installing the caliper mounting bracket and then we'll install the new pads into it.

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