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 FAQ #51
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Tell if my C4 front Brake Discs need changing?
The C4 Brake discs have an inbuilt wear indicator and the recommended minimum thickness is 20mm or 24mm depending on what engine is in the car....

This applies to all C4 models Coupe/Hatch/Sedan/C4P & C4GP

So how do I know when it's down to the limit?

It's not as simple as the minimum wear thickness or wear indicators imply I'm afraid.

It's predetermined by engine type:

ET3J4 - TU5JP4 and (BVM) - DV6ATED4 Minimum 20mm

All other engines: 24mm

[shadowbox=images/c4/brakes/disk_new.jpg|C4 New Brake Disk thickness||right][/shadowbox] Lets start by giving the dimensions of new front brake parts for the C4 VTR+

The Disks when NEW are just over 26mm thick however the 'Wear Indicator' grooves suggest a minimum dimension of 18mm before you need to change discs. (The Overall width - Inner wear Indicator Groove distance)

The image shows the discs as measured very accurately by a Metric Micrometer (not many of you may have one of those!)

The brake pads are actually 19mm thick each (including backing plate) when new by the way. You can visibly see when they are getting worn and you shouldn't let them get too thin.

Mine were last changed when they were down to 12mm (including the backing plate) and whilst theoretically could have gone longer I was happy to change them

[shadowbox=images/c4/brakes/brake2.jpg|C4 Brake Disk and Calliper||left][/shadowbox] Now to explain how the system works and the wear is produced.
The brakes are applied by a single hydraulic 'piston' on each side which sits in a split 'sliding caliper'

When the brakes are applied the pads are pushed against the disks by the brake pistons.

The 'inner' pads contact first and as more pressure is applied the outer pads come into contact with the disks as the calliper slides across towards the piston

[shadowbox=images/c4/brakes/disk_old.jpg|C4 Worn Brake Disk thickness||right][/shadowbox] So the inner face of the disks wear actually faster than the outer!

After 51,600 miles my front discs are still at 23mm in thickness but the wear indicator on the inner side is beginning to 'Sharpen' as can be seen in the image on the left.

It looks like they will need replacing in the not too distant future.

Actually replaced mine at 57,095 miles. They probably could have gone longer but time is going to be tight in the next few months so bit the bullet and changed both discs and pads in just under an hour.
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FAQ Posted by Dave_Retired.
Info Created: 30 November 2008
Last Updated: 14 April 2014