Surely because disks are hot, often wet and made out of a ferrous material it is inevitable that they rust/corrode - But when taking a car for a service/ brake check the corrosion is pushed as a reason to replace them.
Does everybody get told their disks are corroded?
Do you change them?
How long do you expect them to stay free from corrosion?
My relpies are: I get told they are corroded but do not see this as a reason to replace them. When they are replaced I expect them to stay corrosion free until they get wet.
Staying on the subjet of brakes: Do you change the fluid when it is 2 years old, when the lowering of its boiling point indicated the presence of water, or both?
My relpy is: When it boils to soon.
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Surface corrosion on the braking contact area is normal- can be visible overnight.
BUT - discs corrode around the edge, metal flaking off bit by bit. Eventually this reduces the diameter of the disc so much that the pads don't have the full area to contact - this could be the problem. (Happened on my car, even though disc thickness was within spec.).
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Thanks for sharing your experience Sheepy - Am I correct to assume then that so long as your disks have not reduced in diameter so that the pads hang over the edges that you think they are OK? [Assuming also that they still have adeqate thickness].
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IME it depends on how damp your part of the world is, and how long the car stays idle between use.
I used to live in Macclesfield years ago, and the air there is relatively damp - probably to do with the Pennine chain immediately to the east.
Working long shifts, and not using the car for a couple of days at a time, meant the disks were replaced annually: pitted surface, dull and rusty over a large portion of the surface.
These days in a slightly drier climate, with harder pads, and regular use they last several years, but they still corrode in from the edge, reducing thickess in the outer cm. or so, as well as diameter loss.
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I'm sure the metal quality of the disks must be a major factor. Cheap replacements may not be as good as the originals.
The disks on my Volvo are 10 years old and have done 277,000 miles.
They are not corroded or worn. (just passed MOT)
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Forgot to mention this was a new Volvo 240 in 1980, and Volvo dealer fitted replacement disks.
It must also be said the car rusted more than expected too.
Were they using poor steel then, too?
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The quality of the metal is indeed a major factor, although all discs will corrode. I've just had to replace my front discs and had my rear discs skimmed. The front discs were about 4 yrs old and had some corrosion around the edge, but were replaced because they were badly warped (I cooked them on the local bypass). the rear discs had a wedge of corrosion around both the inner and outer edges which would have prevented new pads bedding in properly, so I had the corrosion skimmed off.
Yes, I do replace my brake fluid every 2 years, sometimes more often. I do not wish to find out my brake fluid is no good when the car is fully loaded with family & kit heading for the summer hols (ie the hard way!!). Bleeding is cheap and easy to do, why risk ones life for the price of a round of beers every 2 yrs?
I also replace brake pads before they get to the 3mm minimum material thickness. This layer of material is called the boundary layer and the composition of the material changes in this layer to enable it to be effectively glued to the backing plate. Unfortunately the boundary layer material is considerably worse for braking performance than the rest of the pad (also less kind to discs, and less able to dissipate heat).
The bottom line is this: I want my brakes in peak condition at all times - one day someones life may depend on it.
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I doubt whether it's as simple as that - when I had to replace mine, the diameter was still greater than the area swept by the pads, but a small crescent-shaped chunk had broken off - to a depth of about 5mm - in other words, the disc is potentially weakened even within the bit that's apparently OK.
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With you on that one Sheepy - If chunks started falling off I would be easily convinced to change them. However, it seems to me that everytime I take a car near anyone in the motor trade and let them have a look they always say the disks are corroded and seem to expect me to want to change them - They were corroded last year and they are corroded this year too but their efficiency does not seem to be different so they stay.
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I don't know if just 'waffle', but I recall reading/hearing that since the introduction of asbestos-free friction linings, the disks are now regarded as 'sacrificial' - to be replaced far sooner than in the good old asbestosis days.
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I don't know if just 'waffle', ....
It's not waffle LHM. Asbestos free pads are a lot harder and will wear discs at a higher rate.
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There is some trade off in that pads last longer - on cars in continual use I usually find the first attention needed is about 40k, when both pads and disks require renewal.
BTW always replace pads when fitting new disks or you will find new disks aren't new for long.
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Thats about where I am Harry - 40k. I want my brakes to be in best condition but I wonder if that makes me easy prey for someone who has a mechanic siting on his hands. There is a chain that does lifetime guarantee on brake products but their price is 80% more than the competition [althought I have not yet asked for price match AND lifetime guarantee].
Cyd, do you test the boiling point of the brake fluid before you replace it? Do you have some reason not to trust boiling point testing as a method of quality control?
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at the end of the day, if your disks are within the spec of the manual/mot - theyre gonna be fine - the corrison on the outer of the disk car be removed v. easy - put 1 side up on axle stands(after removing the roadwheel), - chock the other 3, start the engine in first gear, and only 1 wheel will rotate. either use a file, or an angle grinder to revove the rust - easy peasy - dont do this if u have a lsd, or 4 wheel drive- you\'ll find the car at the bottom of the drive
I think you\'d be nuts to do this whatever car you have. This is potentially lethal. I\'ll leave the comment here, but make sure you remember that we are not recommending this and in fact are warning against it. Mark (Moderator)
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I had my pug306 front disc with minimum corrosion for 5 years however the disc runs into minimum thickness after 80000km. (49000miles). Is this ridiculous even having the front pads changed by the agent using Bendix OEM.
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the roadwheel), - chock the other 3, start the engine in first gear, and only 1 wheel will rotate. either use a file, or an angle grinder to revove the rust - easy peasy - dont do this if u have a lsd, or 4 wheel drive- you\'ll find the car at the bottom of the drive
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And you are quite likely to have the file snatched out of your hands and thrown thro the side of your head/eye or any other vital organ you may require later. This is VERY dangerous
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I would concure with RF, this is EXTREMELY DANGEROUS.
Most discs on most cars are fairly easy to remove. I've found it effective to remove them and use an electric sander on them. If you use a fine/medium paper it will remove rust and deglaze the braking surface without cutting too far into the metal.
BTW - When I first started at Austin Rover Cowley in 1983 as an Engineering Student-Apprentice, we had a compulsory 1 days safety training. We were shown some very horrific pictures of injuries that had all happened on the plant. In the intervening years I have personally witnessed what happens when a car falls off its jack onto someone and the immediate aftermath of someones left hand after their sleeve got caught in a cooling fan. I used to know someone blinded in one eye from weld splatter. Please, please, please - don't be paranoid but do be sensible and stay safe.
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>>Thats about where I am Harry - 40k. I want my brakes to be in best condition but I wonder if that makes me easy prey for someone who has a mechanic siting on his hands. There is a chain that does lifetime guarantee on brake products but their price is 80% more than the competition [althought I have not yet asked for price match AND lifetime guarantee]<<
Always ask the garage to return any replaced parts to you.
Hardly suprising they\'re expensive if they give lifetime guarantee on parts which are designed to wear out.
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Huw,
No and no.
When you're already doing a 24k/2yr service, you might as well buy a tub of brake fluid along with all the other items and just do it. It adds about 10 mins to the time to do the service. It would take longer than this (and probably cost more than the fluid) to drive to a garage to get the test done.
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eh, no, if you rest the flat of the file on the TOP of the caliper, then the forces applied to the file are taken up in the caliper, and hence, it becomes stable !!! - i hae ve done this a hundred times to cure a lip on a disk, never has a file slipped !!!!! -don't knock it until you've tried it
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No more on that particular approach please.
A spinning disc and a file which could shatter or be snatched out of your hand seems a silly combination and should not be recommended.
Dave or I will remove any further notes on that line.
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Does everybody get told their disks are corroded? Do you change them? How long do you expect them to stay free from corrosion? My relpies are: I get told they are corroded but do not see this as a reason to replace them. When they are replaced I expect them to stay corrosion free until they get wet.
Re my 98 Mondeo bought with 80K on the clock.
I inspected the disks ( unknown age). There was rust / corrosion in three places.
1. in a small band around the outside and inside unswept face where the pads do not make contact.
2. The outside edge / thickness.
3. (Which no one seems to have mentioned) In all the ventilation slots beween the outside rim and the hub.
I spent quite a lot of time poking, first of all a screw driver and then a file into these holes to get rid of significant chunks of rust . I did this in the belief that these slots help to ventilate /cool the disks.
Gentle tapping with a 4oz hammer on the thickness of the disk also produced flakes of rust.
I accepted a later check result ( minimum thickness ) and had disks and pads changed in spite of them passing a MoT test..
So I expect disks to start corroding in these areas as soon as they are fitted.
On the swept surface, if corrosion does start causing pitting then I would expect this to get worse as the pads do not clean it up.
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>>In all the ventilation slots beween the outside rim
I wouldn't be too bothered about a bit of rust down there, it's when these ribs begin to crack that I worry - because it's so easily missed if you haven't seen it before.
Number_Cruncher
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If a car is presented to a garage and it has corroded discs, when they clearly must have have been used on the trip there then they would be failing in their duty to advise you of such condition? They are not all out to make easy money.
However some places (normally fast fit type places) reward their poorly paid staff with a bonus on parts sold etc; if this is the case then it is suggested using the services of a local well recommended garage instaed who will normally give genuine unbiased advice.
Brake discs are a consumable item on cars now beacuse of harder pads (asbestos free) wearing the disc much more.
Also, light surface corrosion is acceptable, heavy corrosion or pitting is not!
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