Are 'warped discs" a myth

[Tango]

In all my years of driving, including track and hillcimb, I have yet to see a brake disc that is 'warped'. However, it seems to be used as common terminology in multiple forums, and no doubt used by some of the Krap fits as an excuse to flog a new set of discs or a 'skim' to anyone complaining of brake judder. So from my experience I'd say 'warped' discs are pretty much a myth,as I believe it's nigh on impossible to warp a disc under driving conditions. Problems I have experienced are cracked discs and brake pads depositing on the disc unevenly.

 

So in the WIM experience can we finally lay this myth, or is there a case to answer?

[CIH]

Further reading for you Terry

[Tony]

It's a myth, there's two main reasons for the vibration...

1: The drive flange the disc sits against hasn't been cleaned properly, this eventually distorts the disc.

2: Pad matter has been burnt into the disc. This can happen if the driver keeps his foot on the brake ( at the lights for example ) when the disc is very hot. Once friction material is embedded into the disc, steady state breaking will have a pulse because the friction level will be higher where the pad matter is embedded.

[Tango]

Further reading for you Terry

 

All that did was reaffirm my thoughts exactly, as I already believe there's no such thing as a 'warped disc'. I just get a little pi$$ed off every time I hear or read of someone saying 'warped disc' as the answer to any problem of brake judder (including a few on this forum - you know who you are )

[parthiban]

Are we talking about the causes then? Because my discs were warped when replaced (as in they had physically changed shape) so it can't be a myth if it actually happens.

 

The reason the discs warp can vary, but if the discs have changed shape they have warped, and therefore it can't be a myth

[Tango]

Are we talking about the causes then? Because my discs were warped when replaced (as in they had physically changed shape) so it can't be a myth if it actually happens.

 

The reason the discs warp can vary, but if the discs have changed shape they have warped, and therefore it can't be a myth

 

Must be the first recorded case then. How did you check the disc for for consistency of thickness and possible run-out, and are you assuming the discs were machined correctly initially?? If I remember correctly WIM changed your hubs, which were the root cause of the problem, not the discs.

[parthiban]

Must be the first recorded case then. How did you check the disc for for consistency of thickness and possible run-out, and are you assuming the discs were machined correctly initially?? If I remember correctly WIM changed your hubs, which were the root cause of the problem, not the discs.

Yep they replaced everything, think the flanges were warped which in turn caused the discs to warp. But in any case the actual discs were warped (quite badly in fact)

 

It depends what the question is - my experience shows that discs can warp, but it was caused by an external factor (the hubs). But then how do we decide what that is, because in every case surely there will be some other factor that causes the warping, the disc doesn't just do it on its own?

[scorps]

I believe its not a myth, was watching a programme a few weeks ago where the mechanic used a guage fixed to the hub and adjusted the pin to the thickest part of the disc and then spun the disc and you could physicaly see the disc run inwards and outwards back towards the pin.

 

So i say fact

[Tango]

I believe its not a myth, was watching a programme a few weeks ago where the mechanic used a guage fixed to the hub and adjusted the pin to the thickest part of the disc and then spun the disc and you could physicaly see the disc run inwards and outwards back towards the pin.

 

So i say fact

 

But running a disk with a dial gauge only shows run-out, which doesn't necessarily indicate distortion of the disc. I'm referring to a change from the original manufactured state, which, if the disc was originally machined correctly, would have the plane of the mounting surface running true with both sides of the disc braking surface and the disc would be the same thickness over the complete circumference.

For the disc to 'Warp' it would have to be twisted or bent out of shape, and I've yet to see evidence of this, even under extreme heat and brakiing conditions. So I say myth

[SHAHZ]

I believe its not a myth, was watching a programme a few weeks ago where the mechanic used a guage fixed to the hub and adjusted the pin to the thickest part of the disc and then spun the disc and you could physicaly see the disc run inwards and outwards back towards the pin.

 

So i say fact

 

Wheeler Dearers on the Scooby WRX.... i saw that too

[parthiban]

Well if that is the case, then either WIM were wrong or mine really was the first case of "warped discs" - do I get anything for that?

[NickT]

I don't think many places use a Dial Gauge indicator to check for hub run out if the disc replacement is because of brake judder.

Bang on new disks and out of the door......fast krap.

 

Cheapy low carbon disks are more susceptible to this warping.....cheapy chinese krap.

 

Also poor rubber in front suspension can give effect of 'brake judder'.

I remember changing loads of bushes for Sierra owners when I was a poor student as this was mainly the cause.

 

Nick

[adam_r]

This is a very interesting topic!

i would like your input on a situation i experianced at a track day (cadwell).

 

We run a rover 600 ti, not the most amazing car in the world but it was cheap, its fast and does the job.

 

Now, before our track day we fitted a brand new set of good quality discs and pads.. and we ran them in for about 500 -1000 miles using them on the road, obviously increasing brake severity the 'older' the pads and discs got.

 

at Cadwell we experianced something i would call 'warping'. after a few laps and the discs got hotter, on appying the brakes the car would start to shudder.. come off the brakes and the shudder went.

 

Then as the brakes where used more the intensity of the shudder increased to physical (large) movements of the steering wheel, the brake pedal pulsing (not abs) and the whole car shaking to a point we thought it would fall to bits!

 

we drove around for a few laps to let the brakes cool, using them as little as possible.. back in the pits and let the car cool down (in gear so no pad was touching the discs)

 

this happened on the next 2 outings but suddenly seemed to get better and better until it had more or less gone away, and now we dont seem to experiance this at all.

 

 

can anyone explain what was going on with our brakes ?

[andyelcomb]

This is a very interesting topic!

i would like your input on a situation i experianced at a track day (cadwell).

 

We run a rover 600 ti, not the most amazing car in the world but it was cheap, its fast and does the job.

 

Now, before our track day we fitted a brand new set of good quality discs and pads.. and we ran them in for about 500 -1000 miles using them on the road, obviously increasing brake severity the 'older' the pads and discs got.

 

at Cadwell we experianced something i would call 'warping'. after a few laps and the discs got hotter, on appying the brakes the car would start to shudder.. come off the brakes and the shudder went.

 

Then as the brakes where used more the intensity of the shudder increased to physical (large) movements of the steering wheel, the brake pedal pulsing (not abs) and the whole car shaking to a point we thought it would fall to bits!

 

we drove around for a few laps to let the brakes cool, using them as little as possible.. back in the pits and let the car cool down (in gear so no pad was touching the discs)

 

this happened on the next 2 outings but suddenly seemed to get better and better until it had more or less gone away, and now we dont seem to experiance this at all.

 

 

can anyone explain what was going on with our brakes ?

 

I'd say that despite your efforts to cool the discs you still had some hot spots and pad deposits on the discs which led to the shaking as the discs rotated. This will have been either cleaned off in time, or spread evenly on the disc.

Unfortunately even though you may have stopped without using the brakes, the pads will still have been lightly touching the discs and thereby suffering heat soak / glazing in line with the pads. Sometimes you can get pockets of hot gas produced between the pad and disc and this can lead to localised expansion.

The only way to avoid that is to have the car up in the air and slowly turn the wheel whilst cooling to avoid any hotspots.

[scorps]

I believe its not a myth, was watching a programme a few weeks ago where the mechanic used a guage fixed to the hub and adjusted the pin to the thickest part of the disc and then spun the disc and you could physicaly see the disc run inwards and outwards back towards the pin.

 

So i say fact

 

Wheeler Dearers on the Scooby WRX.... i saw that too

 

 

Yeah that was it.......maybe warped means run out in the trade?

[HighlandPete]

Yeah that was it.......maybe warped means run out in the trade?

 

I'm sure localised contamination, corrosion, run-out, are all bagged together as 'warped' to many.

 

A badly mounted disc with resulting run-out, can be forced to 'sort of warp', during braking, to try and run true. So after removing, if measured for run-out it, can actually read as 'warped'.

 

HighlandPete

[TheBoy]

I have certainly had "out of shape" front discs on more than one occasion. I think that any out of shape is simply classed as warped. IME, the out of shape is where the thickness varies, rather than an actual 'buckle'

 

A skim does cure it, though in the case of my Vauxhalls, new discs and pads are so cost effective at the dealer if you have access to the Vauxhall Trade Club scheme, I just replace them. On the Omega, its rare I do that sort of damage to the discs, except when I had some low quality pattern ones on.

 

The little Rover, Mrs TheBoy's car, well, errr, uhmmm, yes, what can I say :angry: - the discs are too small imho, and very prone to getting far too hot, and often ultimately causing the discs to sometimes go out of shape/warp.

[aussie aligner]

Are we talking about the causes then? Because my discs were warped when replaced (as in they had physically changed shape) so it can't be a myth if it actually happens.

 

The reason the discs warp can vary, but if the discs have changed shape they have warped, and therefore it can't be a myth

 

Must be the first recorded case then. How did you check the disc for for consistency of thickness and possible run-out, and are you assuming the discs were machined correctly initially?? If I remember correctly WIM changed your hubs, which were the root cause of the problem, not the discs.

 

fact...... can anyone explain how heat affects steel? then what about when super hot rotors being drastically cooled?

the only way it could happen in your logic is, if the rotors may have been removed or you were so unfortunate that a piece of debris fell behind when wheels where removed!! remember they don't make them like they used too

[Tango]

fact...... can anyone explain how heat affects steel? then what about when super hot rotors being drastically cooled?

the only way it could happen in your logic is, if the rotors may have been removed or you were so unfortunate that a piece of debris fell behind when wheels where removed!! remember they don't make them like they used too

 

I agree that if the manufacturing process has induced stresses in the material that haven't been removed by heat treatment before final machining, then further heat from braking can cause distortion. If they haven't been manufactured properly then that will be the inevitable conclusion. The only other way I know of changing the shape of steel or cast iron is differential temperature variation, e.g. heating up one side or one area of a component and cooling another, so again it's theorectically possible if the rotor is really hot from braking and is then splashed with water.

In saying all that I've yet to see a 'warped' rotor/disc.

[TheBoy]

Certainly one way I have 'warped' (probably affected the uniformness of thickness, than buckled/bent disc) pattern discs on my Omega is by 'giving it some large' (I work in Milton keynes, any attempt to be in a hurry does ask a bit from the brakes, esp with a 1.7 tonne car), then being lazy at the next roundabout, sat with my foot on brake waiting for my gap (its an auto, so there is creep otherwise).

 

It seems, get cheap discs very hot, then compress it in one place quite hard between 2 pads is a sure way to need new discs (and pads)

[Tango]

Certainly one way I have 'warped' (probably affected the uniformness of thickness, than buckled/bent disc) pattern discs on my Omega is by 'giving it some large' (I work in Milton keynes, any attempt to be in a hurry does ask a bit from the brakes, esp with a 1.7 tonne car), then being lazy at the next roundabout, sat with my foot on brake waiting for my gap (its an auto, so there is creep otherwise).

 

It seems, get cheap discs very hot, then compress it in one place quite hard between 2 pads is a sure way to need new discs (and pads)

 

That,s more likely to be transfer of the friction material from the pad onto the hot disk which is quite common and probably the biggest cause of people saying they've 'warped' their discs.

 

http://www.stoptech.com/tech_info/wp_warped_brakedisk.shtml

[TheBoy]

Certainly one way I have 'warped' (probably affected the uniformness of thickness, than buckled/bent disc) pattern discs on my Omega is by 'giving it some large' (I work in Milton keynes, any attempt to be in a hurry does ask a bit from the brakes, esp with a 1.7 tonne car), then being lazy at the next roundabout, sat with my foot on brake waiting for my gap (its an auto, so there is creep otherwise).

 

It seems, get cheap discs very hot, then compress it in one place quite hard between 2 pads is a sure way to need new discs (and pads)

 

That,s more likely to be transfer of the friction material from the pad onto the hot disk which is quite common and probably the biggest cause of people saying they've 'warped' their discs.

 

http://www.stoptech.com/tech_info/wp_warped_brakedisk.shtml

Potentially, but in at least one case I've had (on the Rover), it was the disc itself was thinner in one area - we had to have the Rover engineers check them, as Rover were getting miffed at the number of warranty replacements I'd had - opps!)

[Rich]

So the brakes on my brothers escort cause a juddered, which disappears when you let go of the brake. The discs look like they have some surface rust on them (maybe from lack of use) but are still quite thick and the pads have lots of meat. So are new discs/pads needed or could they be cleaned along with hub and see what happens? Just seems a waste of time doing that if they will need replacing.

[Rich]

So is it worth cleaning the discs, pads and hubs to see if it makes a difference?

[parthiban]

Don't you need to measure the disc runout though to see if it is warped? If not then it might be worth cleaning it up as a first step.