V50 Brakes : Do brake discs really warp?...I'm not so sure they do...

[Volvo6]

Had several instances of the garage telling me that my brake discs have warped on the V50, accompanied with the familiar vibration through the steering wheel when braking.

However while there was always no doubt the issue was with the brakes I was unconvinced that "warping" was actually the cause. I had had the car for 70 of its 83k miles and while I will admit to often driving in a spirited manner I could not believe that I had managed to go the first 40k on one set of discs, with no warping, and then all of a sudden they were lasting just a few thousand before the vibrations came back without something else playing a part.

I was given explanations like "perhaps you drove through a puddle while the brakes were hot and that warped them" or "they might warp if you really drove like a racing driver" and from one Volvo garage "the other Volvo garage you went to last time must have fitted non-Volvo parts"

Having done some reading around the subject and physically examined the discs that supposedly "warped" I have reached a different conclusion; what is actually happening is that deposits from the brake pads are sticking to the discs when very hot and leaving an uneven surface on the discs...causing the vibration. The reason this happens, as I surmise, is that after going for a blast down a country road I would then possibly sit at the lights for a few minutes with just the foot brake on and all the while fragments of pad were being burnt onto the surface of the disc. An examination of the discs revealed obvious imprints in the shape of the pads.

I reasoned that perhaps I was getting lazy about using the handbrake over time and that this was the cause. I have subsequently changed my ways to always use the hand brake for all but the briefest pauses and so far at least, no matter how much I use the brakes they remain smooth...

So my question is...is "warping" really a myth? I mean it seems unlikely that a cast iron lump would actually change shape at the sort of temperatures that a road car would achieve in the brakes...perhaps deposits from the pads are the more likely culprit in most cases and if people used their handbrakes more rather than clamping a hot pad to a hot disc while at the lights there would be less of these "warping" cases.

Thoughts?

[scoobysn7x]

I have had a few cars that had warped discs which caused vibration issues, all of which were solved when the offending discs/pads were replaced, the last time it was due to a sticking caliper that was heating the disc to a lot higher temps and for longer than it was probably designed for, cheap parts can also be to blame.

But I did read an article somewhere that the biggest cause was breaking to a stop and then sitting with the footbrake on as this keep the hot pads in contact with one area of the disc and heats it up more, the article said best thing to do is when braking hard or braking to a stop is to brake, get to a virtual stop the let off the foot brake so you not keeping the hot pads in contact with the disc, so I've started doing this only time will tell if it works.....

[kane]

I had exactly the same problem several months ago after a small stone had gotten stuck between the pad and disc. It started off small but over time the wheel wobble became much worse but still only when braking.

I changed just the discs and then the problem was fixed instantly. In my mind there is no doubt what so ever that the disc had warped.

[v40bart]

I for one do not believe that discs warp. It never happened to me not in one of my four cars and five motorcycles I have owned. I've seen this on many motorcycle forums and one of the mags (can't remember which it was yonks ago) did a feature on this backed with lab tests. It turned out that in many cases it was the pad material getting stuck to the discs that was causing the vibration. Quick hone and a pads replacement was usually enough to solve the vibration. The only way to check for warping is to measure for run-out and even that can be cured with a quick skim on a lathe if the disc in question is nearly new. Apparently what matters is how you wear in your brakes and discs. The method I read about is somewhat unorthodox, it should be floating about the internet somewhere.

[jaygee]

I get a slight judder under braking. I have put it down to something in the calliper and or the pads.

The only problems in the past with discs were that they were corroded.

[Volvo6]

I changed just the discs and then the problem was fixed instantly. In my mind there is no doubt what so ever that the disc had warped.

Yes possibly if caused by a stone; I was mainly talking about the claim that brake discs can warp through heating and/or rapid cooling and how I think real cases of that are very rare and are more often than not actually caused by pad material on the discs.

The main reason I brought the subject up is that I feel the garage gave me incorrect information through their own ignorance of the problem; if the issue had been better understood and instead of their dubious assertions about puddles or fake parts I mentioned in my first post they had told me that the issue was with pad material...which I had to find out for myself I could have saved a few sets of discs.

[SiRS2000]

Originally Posted by Volvo6

I would then possibly sit at the lights for a few minutes with just the foot brake on and all the while fragments of pad were being burnt onto the surface of the disc. An examination of the discs revealed obvious imprints in the shape of the pads.

I reasoned that perhaps I was getting lazy about using the handbrake over time and that this was the cause. I have subsequently changed my ways to always use the hand brake for all but the briefest pauses and so far at least, no matter how much I use the brakes they remain smooth...

I have always been told that the main casue of warped discs is holding the car on the foot brake and not the handbrake. reason being is the section of disc that is held by the brake pads can not cool as quickly as the rest of the disc. Now if you imagine how hot your discs are especially if you have been driving a bit keen down the back lanes and then come to a junction / lights.

The lack of handbrake use was the main casue of a lot of 80's & 90's hot hatches eating their way through brake discs.

[benr7310]

http://www.youtube.com/watch?v=iSrJU8rt5fE

warped disks are not a myth.

[GMad]

I too have had a few cars that have suffered with warped discs and they don't have to be too far out of true to cause terrible vibration under braking.
Given that brake discs are so inexpensive, it is a cheap and easy fix

[v40bart]

Originally Posted by benr7310

http://www.youtube.com/watch?v=iSrJU8rt5fE

warped disks are not a myth.

Never said it was, mate. It just doesn't happen as often as garages would like you to believe.