My dad replaced my front brake pads today and since the pedal feels spongy and I have to press harder to get a response. He says that this is normal and brake pads have to be driven a couple of hundred miles to wear them in and then they'll be better, but my friends have told me that this isn't normal or safe and I need to bleed my brakes. Here's my problem, I need to drive my car and its a bank holiday, who's correct?
If the system wasn't opened, there is no need to bleed the brakes. It isn't normal for you to need to break in the brakes. Make sure the rear are properly adjusted.
June, 3, 2012 AT 9:46 PM
NOTE: If the brake pedal is hard to push, make sure the power brake assist isn't disconnected.
June, 3, 2012 AT 9:54 PM
I've no idea to be honest, I don't know a lot about cars. When I suggested to my dad that the brake might need bleeding he said that it didn't because no air could have got in and just keeps saying that I need to wear them in. Just seemed a bit dangerous to me because the breaks aren't as responsive as they were before the pads were changed and I was expecting them to be really responsive. Dad says they will get more effective as they wear in because they'll fit to the grooves in the brake discs which they aren't at the moment. Friends have told me that air can get in even if you are changing the pads and the system will need to be bled. I wanted a professional opinion before I started driving around, for obvious reasons.
June, 3, 2012 AT 11:37 PM
Your dad is right. You need new friends if you're going to listen to them for car advice. Your old rotors will always have grooves worn into them and the old linings wore to match those grooves, so they were making 100 percent contact. It's a normal part of any brake job to machine the old rotors to true them up but even that leaves very small grooves, just like a phonograph record, and it can take 100 miles or more for the new linings to wear to match those grooves. Since most people don't have a brake lathe to machine the rotors, they often get reused just as they are, grooves and all, so your pop is exactly correct, it's going to take some driving and stopping before they are fully seated.
Here's where a lot of people run into trouble, including mechanics. You have to understand, as you already found out, that the braking power isn't what it used to be. Most people don't even notice, they just go driving like normal, not realizing there is that break-in period. To clarify, Jacobandnickolas was correct when he said there is no break-in period for new pads. He's talking about parts being unable to do their job until they go through a break-in period. Brake linings are 100 percent able to do their job right out of the box. What I'm referring to is different. It's other conditions that impede their performance, namely wearing to the rotors' grooves. I'm just referring to them wearing to match the rotors' friction surfaces, THAT'S when your braking performance will be back to normal, just like your dad said.
What all mechanics or shop people should tell you but they usually forget is to take it easy for the first few hundred miles. If you do a lot of city driving, that's when brakes can get really hot and lose their "coefficient of friction". That just means they don't grab very well. In response to the lower braking power, you push harder on the brake pedal, and that makes the brakes even hotter and the problem just keeps getting worse. In extreme cases no matter how hard you push the pedal, it will be high and firm but the car just keeps on going. That is one type of "brake fade". Once that happens, the cure is to let the car sit for a couple of hours so the brakes can cool down, then go drive it like normal.
To start that process of the linings wearing to match the rotors, mechanics will always perform a test drive to check for noises and proper operation, and during that drive they'll perform two or three really hard stops with some time in between to let the brakes cool down. That's just the start though. They still should tell you to take it easy for a few days and don't expect the car to stop like it did before, ... For a few days. Some shops, especially mass merchandisers even hang an information tag from your mirror in case they forget to mention that.
As for getting air in the hydraulic system, ask your friends how that could happen and why it doesn't happen all the time? There actually is one condition but if it wasn't affecting your car before, that isn't going to change from replacing the pads. Old brake fluid that hasn't been changed regularly, (like how many of us actually do that?), Will absorb moisture from the air if the system is left open, such as leaving the reservoir cap off too long or leaving the cap off the bottle of new brake fluid. Brake fluid loves moisture. Brake fluid boils at somewhere well over 400 degrees F. If there's enough moisture in the brake fluid, besides leading to corrosion, that moisture will boil at 212 degrees F. It turns into steam which can be compressed. That leads to a different type of brake fade. Overheating the linings, which I described earlier, leads to "gasing" where the binders in the lining material gives off gas and that gets between the rotor and linings and acts like microscopic ball bearings. You'll still have a nice high hard brake pedal; the car just won't stop. Brake fade due to moisture results in a low and mushy pedal due to the resulting air compressing when you press the pedal. The brakes do not have to overheat to cause that. It will occur from normal driving. Bleeding that air out will solve the low mushy pedal for a little while but eventually the problem will come back and you'll be scratching your head wondering where that air is coming from. Adding new brake fluid while bleeding some of the old stuff out is the fix but your car is too new to be thinking about that.
Now go thank you dad and take it easy on the brakes for a few days.
June, 4, 2012 AT 12:03 AM
Thanks very much guys! I figured my dad wouldn't let me drive the car if it was dangerous but I'm a bit of a worrier especially when people were telling me I need to bleed the brakes or I'll end up not being able to stop. Thanks again for the advice!