My motto is a car can break down, in fact it's within any Mechanical nature for it to eventually fail but brakes MUST STOP.
When you go to change the pads on your car there are also a few things to observe.
1. Check the condition of the disc, if there are groves in the disc or if you experience vibration through the brake pedal when you brake then you should consider a disc machine. If you have a 4wd or a fixed disc, then you can get what we call an on car disc machine, but most cars these days cars are fitted with a floater disc, easy to take off and send for machining, glazed disc's or if the surface is too smooth, you can rough up the surface before installing new pads, most mechanics will get the disc machined even if it's not any of the above, i feel this is an unesessary repair and an added cost to the customer, you would be looking at $40 per disc, so it adds up to the final bill, i only get the disc's machined if they need machining. You should also bear in mind that when you machine a disc, it takes the life off the disc and can heat up more than usual as the disc is thinner, the disc should also be measured (thickness) before considering a disc machine, if the disc is too thin, it will not be able to be machined and then you will have to install new disc's. The size or min thickness are written somewhere on the disc.
2. Another point to consider is to remove the caliper slides, clean and lube them with every pad changed.
3. After the car has the new disc pads fitted, leave the wheels raised and gently pump the brake pedal with the engine off until the pedal becomes hard. Then go to the wheels that have the new pads fitted and spin the wheel by hand, if the brakes are not tight and releasing ok, then put the car back on the ground.
4. The most important part of a pad replacement is to do the bedding in. Bedding in is a term used to get the surface of the pad true to the disc. You do this by driving the vehicle around 20KPH, lightly touching the brake pedal, do this 50 Meters at a time for about 400 meters, you will notice that before you bed in the brakes, the pedal will seem a little spongy, do not be concerned about this, the pedal is spongy untill the pad has bedded in and will be that way for 100 to 200 K.M. the pedal height should come up a bit and after you have finished the bedding in process the pedal should be back to what you are used to. The braking distance should not be affected by new pads, it should stop in the required time, if it doesn't come back up, don't try and fix it yourself, take it to a professional to find the cause and repair.
Note: If you are not confident to change the pads yourself, DO NOT ATTEMPT to do the job, call a professional to do it, for an hours labour is a small price to pay for your safety!!!
Note : If you use a cheap pad, then expect it to squeal and the bedding in process will take longer. I use a bendex Pad or a Repco chamfered pad, i have found the $20 extra to buy good quality pads makes all the difference to your stopping power, why would you buy a cheap noisy pad to save a couple of bucks, remember cars will brake down, but BRAKES MUST STOP!!!