
What that noise probably is
Knocking over bumps, squealing on turns, a hum that rises with speed. What each one usually means.
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Anywhere between fifteen and fifty thousand miles, which is a useless answer until you know what moves the number. Mostly it is how and where you drive, not what you bought.
Pads are a consumable, like tyres. The question is never really how long they last, it is whether yours are wearing faster than they should be and why.
The short version
A car doing motorway miles can see fifty thousand. The same car in town, driven hard, can see fifteen.
The honest answer is that you cannot tell by feel until they are nearly gone, which is why they get measured at every service and the figure written down.
A wear indicator squeals when the pad is near its limit and stops squealing when you brake harder. That is a book-it-in noise rather than a panic. Grinding you can feel through the pedal is the other one, and that means stop.
Not always, and anybody who says always is selling something. Discs have a minimum thickness stamped on them and we measure against it.
What does force discs is lipping, scoring or warping. A pronounced lip at the edge means new pads will never bed properly, and in that case doing pads alone is throwing them away.
Budget friction material glazes under heat, fades when you need it most, and is abrasive enough to eat the disc it runs against. The saving is small and it is spent twice.
If you want the detail on what a brake job involves, the brakes page sets out what is included and what gets measured.

Knocking over bumps, squealing on turns, a hum that rises with speed. What each one usually means.
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No, and the regulation that says so has been in place since 2003.
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Half the batteries we are called out to are fine. Usually it is the alternator or a drain.
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Brake work runs mobile across the whole patch, and a typical axle fits comfortably inside a morning.