Why is my brake disc blue? - Renault Forums :: Independent Renault forum

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post #1 of 26 (permalink) Old 13th April 2007 Thread Starter
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Why is my brake disc blue?

Hi All,

My car is currently in the local Renault rip off dealership getting a service, aswell as the service they are looking for the cause of a vibration that comes from the passenger side front wheel area.

They have just called me and told me that the disc on the passenger side is blue which has been caused by it overheating and they believe this may be causing the problem.

My question is:

Would overheating cause the disc to turn blue and if so could this be causing the vibration problem?

The vibration itself, although it doesn't happen all the time, can get very loud and does stop when lightly applying the brake - it also stops when turning the wheel slightly and when the car goes over any bumps in the road.

Can anyone confirm what they are saying is right as if this is the cause I will replace them myself rather than paying the £226.75 they want to do it!!!

Cheers
Fraser
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post #2 of 26 (permalink) Old 13th April 2007
selwonk
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Have a look at this page:

Ride Drive Ltd UK, Advanced Driving, Advanced Driving Course, Advanced Driver Training

Quote:
Originally Posted by Description of overheated disks
If you abuse your brakes, and cause them to overheat, their efficiency will become diminished and you will get a condition that is commonly referred to as brake fade. In extreme cases the brake discs will turn blue in colour, this decolouration being caused by excessive heat that irreversibly changes the molecular structure of the metal, and the surface of the pads will become glazed. The result is they no longer work properly and the whole assembly has to be renewed.

Something else you can get from overheating your brakes that causes brake failure, especially if you have not serviced and maintained them effectively. Brake fluid, lik eall liquids, has a boiling point, as doe water. However, in the case of brake fluid,, that boiling point is at a much higher temperature than that of water, but if it does boil, i twill turn to vapour.
Src - RideDrive.co.uk

Last edited by selwonk; 13th April 2007 at 01:05 PM.
post #3 of 26 (permalink) Old 13th April 2007
selwonk
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Just one side? That's unusual and might indicate a problem specific to that corner. Hopefully one of our techs might be able to shed some light on what might cause that. Maybe a binding caliper or something?
post #4 of 26 (permalink) Old 13th April 2007 Thread Starter
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Originally Posted by Description of overheated disks
If you abuse your brakes, and cause them to overheat, their efficiency will become diminished and you will get a condition that is commonly referred to as brake fade. In extreme cases the brake discs will turn blue in colour, this decolouration being caused by excessive heat that irreversibly changes the molecular structure of the metal, and the surface of the pads will become glazed. The result is they no longer work properly and the whole assembly has to be renewed.

Something else you can get from overheating your brakes that causes brake failure, especially if you have not serviced and maintained them effectively. Brake fluid, lik eall liquids, has a boiling point, as doe water. However, in the case of brake fluid,, that boiling point is at a much higher temperature than that of water, but if it does boil, i twill turn to vapour.


Thanks for the above but the brakes work absolutely fine, the only problem we have is the vibration and the dealer is saying this "may" resolve it. Their reasoning being that the disc is blue so it must have overheated.

I had the brakes apart a couple of weeks ago, cleaned everything up with a wire brush and put copper grease on the back of the pads just to be sure. I checked the disc and other than the usual flakey rust around the edge of the disc it didn't seem warped or anything.

I was just checking to see whether what they had said was right!!
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post #5 of 26 (permalink) Old 13th April 2007
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Sounds like a sticky caliper ... does one wheel get much more brake dust than the other? if so then the caliper is sticking which in turn will cause the disk to overheat (may also cause caliper damage if severe,) this in turn will cause the disk to warp (runout) .... the likely cause of the vibration your experiencing.

If its under warranty have a tantrum with the service dept ... otherwise if your up to it change the disks, pads, brake fluid (DOT 4 I think) and dont forget to change the caliper mounting bolts, and watch the ABS sensors .... they can be quite fragile. Plus check the caliper seals to establish whats causing it to stick!

Lets know how you get on.

Hope it helps

Why is it the older I get .... the better I think I was ?
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