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Discussion Starter #1
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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Have a look at this page:

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

Description of overheated disks said:
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
 
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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?
 

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Discussion Starter #4
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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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 :)
 

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Discussion Starter #6
Thanks for the advise but to be honest, I haven't checked the other side to compare them as the noise has only been coming from that side - I will do that tonight though.

I do have another question though - if it is a sticky caliper what difference would changing the discs, pads and brake fluid make - wouldn't the caliper still be sticky or is that where the caliper bolt change comes in?

Also on a completely seperate note - does the dCi have a turbo? I was under the impression it was a non turbo and was just direct compressed injection or something similar?
 

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Thanks for the advise but to be honest, I haven't checked the other side to compare them as the noise has only been coming from that side - I will do that tonight though.

I do have another question though - if it is a sticky caliper what difference would changing the discs, pads and brake fluid make - wouldn't the caliper still be sticky or is that where the caliper bolt change comes in?

Also on a completely seperate note - does the dCi have a turbo? I was under the impression it was a non turbo and was just direct compressed injection or something similar?
Hi, you should also check the caliper slides and the piston seals for dirt/corrosion (look for a split piston dust cover ... usual cause) and clean everything with brake cleaner solvent ... the caliper bolts should be changed as they are one use only, and wont torque doen properly if they have been used before without using a threadlock compound .... best to change them.

All the dCi engines are turbocharged I believe .... its a very long time since any manufacturer sold/fitted a diesel engine that was not blown.

Hope it helps :)
 

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Blue Brakes Oh how naughty OOH!

A blue coloured brake disc is a sign that it has been seriously overheated at some stage. When tempertaures as high as this are reached it is likley to cause other damage. Such as damaged seals in the caliper, boiled brake fluid, fried wheel bearing, burnt or hardened drive shaft boot (need I go on). If it were mine I would replace both front discs, both front calipers and of course the brake pads. I should also be noted that copper grease should not be used anywhere near brakes - if lubricant is required it must be proper brake grease.
Remember brakes are like your best friends "You miss them most when they're not around":)
 

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Discussion Starter #9
A blue coloured brake disc is a sign that it has been seriously overheated at some stage. When tempertaures as high as this are reached it is likley to cause other damage. Such as damaged seals in the caliper, boiled brake fluid, fried wheel bearing, burnt or hardened drive shaft boot (need I go on). If it were mine I would replace both front discs, both front calipers and of course the brake pads. I should also be noted that copper grease should not be used anywhere near brakes - if lubricant is required it must be proper brake grease.
Remember brakes are like your best friends "You miss them most when they're not around":)
Would it not be overkill to replace both calipers when the noise is only coming from one side?
I don't think there is a problem with the caliper and it seems to be moving smoothly and freely and all seals look OK?

Also what is the problem with putting a little copper greas on the back of the brake pads before replacing them?

Cheers
Fraser
 

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Blue Blue brake pads (I feel a song coming on)

You talking about over kill or too expensive LOL. The amount of heat required to turn the disc blue is likely to have damged the internal seals in the caliper so if you replace one side and not the other you are likely to have unequal braking (oops who put that telegraph pole there) causing the car to swerve whilst braking and also fail MOT. Copper grease is not recommended because it's melting point is too low and when the brake heats up (as naturally it will) it will run onto the braking surfaces (oops here comes another darned telegraph pole) causing severe loss of braking power. Remember your good friends.:d
 

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Discussion Starter #11
You talking about over kill or too expensive LOL. The amount of heat required to turn the disc blue is likely to have damged the internal seals in the caliper so if you replace one side and not the other you are likely to have unequal braking (oops who put that telegraph pole there) causing the car to swerve whilst braking and also fail MOT. Copper grease is not recommended because it's melting point is too low and when the brake heats up (as naturally it will) it will run onto the braking surfaces (oops here comes another darned telegraph pole) causing severe loss of braking power. Remember your good friends.:d
thanks for that - I don't think I will be changing either of the calipers (partly due to cost and partly because they seem fine) but will be doing the discs and pads, nice to know about the copper grease aswell though!

Anyone know if the caliper bolts are only available from the dealers and if this is really a neccessity?

Cheers
Fraser
 

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Oh my blue blue brake discs

Caliper guide pin bolts are a once only fttting and should have a locking compound smeared on the threads before fitting. It can't be stressed enough that these bolts be replaced as the security of the brake asembly relies on their integrity. Most decent brake pad sets come with new bolts supplied and like brake discs can be sourced from most decent motor factors at a much less cost than renault. I use a brand called APEC and have found them to be OK. Many motor factors also supply refurbished calipers on a replacement basis. I still strongly recommend you replace the calipers but if you are determined not to do so - please replace the brake fluid as it will have suffered from the effects of overheating causing brake fade (oops here comes another telegraph pole). Just remember the old adage "Buy cheap and you end up paying twice" and if you are not concerned about your own safety or that of your passengers (poor old granny) - please consider the safety of other road users.:mad:
 

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Steel turns various colours of blue at a temperature range of around 280 to 320 degrees centigrade this is almost 3 times hotter than boiling water.
Now I'd guess the steels used in a disk brake contains a fairly high amount of carbon which makes them last longer, if the disks have been up to almost red heat this will have trashed the hardness of the steel used in the disk.
I certainly would keep my eye on the future wear of this disk with frequent checks.
 

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My blue brakes Ouch!

Well done Hondo - a good bit of knowledge there. If it affects carbon steel or cast iron just think what 300C will do to the caliper seals and the brake fluid - the mind boggles. In the past I used to go and watch night-time rallying and you could see the front brakes on the cars glowing red and sparks flying - it was great fun to watch and although I'd heard stories about brakes glowing red I really didn't believe it until I actually witnesed it for myself. Most people just don't realise the amount of work and stress that brakes have to take even in everyday motoring and then they whinge about the cost of decent repairs.:steam:
P.S. The boiling point of brake fluid is 155 - 230 degrees centigrade - well within the temperatures to make steel/cast iron turn blue.:)
 

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first and fore most :- does the car brake in a straight line under heavey breaking . if not and it pulls to the side with the "blue disc" then suspect brakes (prob calipat sticky)
 

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Blue discs

See your point Ev - but what would that test tell us about the condition of the discs and calipers. Think about the efects of having 2 equally bad calipers or discs and if ABS is fitted it can hide the effect of uneven braking - furthermore it wouldn't tell you if a caliper wasn't releasing properly. Otherwise it sounds very scientific.:rofl: :rofl:
 

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Copper grease is not recommended because it's melting point is too low and when the brake heats up (as naturally it will) it will run onto the braking surfaces (oops here comes another darned telegraph pole) causing severe loss of braking power.

Sorry madnoel10, I was under the impression that copper grease/coppaslip etc was not susposed to be used, as it does NOT burn off, therfore if it contaminates the pads/disk surface it will not burn off and stay there acting as a lubricant.

Its unlikely to be because of the melting point being too low as coppaslip state the melting point is in excess of 2000 degrees fahrenheit which is 1090 degrees celsius .... far hotter than any steel braking system will ever run, even if overheating.


Hope it helps :)
 

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Copper grease not suitable for brakes

See your point Truckbus as it contains copper and clay as a thickener it will take high temperatures to melt the copper but the medium in which it is mixed will melt far sooner. When using grease close to brakes the melting point isn't the real issue as the dropping point (the temperatrure at which it will soften and start to run or drip) is much more important. My research says the drop point is 300C which is well within brake operating temperatures. At this temprature it will begin to run and possibly contaminate brake components and any copper going with it will act as a lubricant. Most importantly it contains chemicals which attack brake rubber components. If it was suitable I'm sure brake manufacturers would recommend its use and to date I have never heard of any such recommendations (although I may be corrected):)
 

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Hi madnoel10, Mmmmm interestingly Molyslip ... the people who make Copaslip dont seem to agree (not surprisingly I suspose) :rolleyes: ...

In the automotive industry:​

Copaslip is recommended by major automotive manufacturers for use as a lubricant behind disc brake pads​
to prevent brake squeal and for application to pivot points and adjusters on drum brakes to facilitate adjustments.
They also state that it doesnt have a drop point as its a "non-melt" product .... for the technical sheet see this

http://www.molyslip.com/WebPDF/Copaslip.pdf

I had a look on the Ferodo, Mintex and EFI websites and couldnt find any "warnings or prohibition notices", have you got any links? ... I'm interested now!

:)
 
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