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Re: clio 3 brake discs and pads
This is a direct lift from the Honest John website :-
Q - BRAKE DISCS AND PADS: Why do brake discs as well as pads need replacing so often? And why is it usually rear discs first?
A - Ever since asbestos was banned from brake pad material, and also to keep pace with the increased performance of modern cars, manufacturers have had to add metal to pad material and to make brake discs softer and sacrificial.
Rear disc brakes pose an additional problem. The front brakes do most of the actual retarding of the car. The rears merely balance this in extreme braking conditions.
Discs also rust all the time, especially overnight in a winter salt-laden, wet atmosphere. That's why the metallic content of the parking brake pads sometimes stick slightly to the discs when you release the parking brake first thing in the morning. They have effectively rusted together.
Your first brake of the morning cleans the surface rust off the front discs and you can often hear it as a grating sound. But unless you (first check your mirrors) and brake very hard, the rear pads take much longer to clean surface corrosion off the rear discs.
This gives oxidation a chance to eat deeper into the metal with the result that rusted rear discs start to adopt a grooved appearance. At this point braking efficiency is severely compromised and the car would probably fail an MOT.
Seems to explain your issue rather well. You'll need to change the pads as well because the old ones are shaped/grooved by the old disks. They wouldn't be efficient or safe to use with new disks.
As for how long they should last, is similar to the how long is a piece of string. Depends on the size of disks, weight of car, engine power as well as the style of driving.
If unhappy, you could also get a second opinion from an independent garage. I was advised by Renault my rear pads needed changing soon, They lasted the best part of a year before change became neccessary.