Diagnosing Worn/Warped Brake Disc Query

Griffo · 22 Oct 2008 at 08:13

Morning,

I'm due to get the vRS serviced soon and apart from it being filthy I have one 'concern' which is that I think the rear pads need changing.

It's making shiny noises from the rear brakes when coming to a stop pretty regularly now, I presume I'm making a half-correct assumption that this is the pads.

Oh yes, my question is this: How can I tell if the discs are warped? (oh, and is there a specific thickness that = worn?) My main concern is I don't trust anyone, I'll take it into the specialist place I found in Reading and they'll say "oh yar matey, yee pads need changing but yee olde discs are warped/worn badly so we'll have to replace those ARGH matey!" to which I will respond "oh, k" and spend lots of money".

Thusly I would prefer to be equipped with the knowledge beforehand whether or not whatnot is borked. Are warped discs always noticable when driving? I.e. juddering?

I'd take a photo for your viewing pleasure but I strongly believe photos of cars steal their souls (the wheels have too many spokes/I am lazy).

Thanks in advance for any help/insults/bits of cake thrown this way.

Toker · 22 Oct 2008 at 09:25

I wouldn't worry about warped brake discs, they are pretty much a myth. It's nigh on impossible to warp a disc.

The main problems with discs are cracked discs and the pads depositing on the disc unevenly (the latter often being misdiagnosed as a warped disc due to judder feel).

If they are normal discs you can check the wear by the metal lip around it, if it is prominant, then they are worn (although some people just take a grinder to the lip and get more life out their discs)

Firestar_3x · 22 Oct 2008 at 10:00

Problem with discs is they have a minimum operating thickness before they need changing, for example 25mm when new and 23mm is worn needing replacement.

Odds are its the rear pad squeelers letting you know the pads are done.

Don't let the dealer do the work they always charge a fortune for brake related fixes.

Rilot · 22 Oct 2008 at 10:59

Jack the car up, whip a wheel off and look at the pads. Squealing usually means they're worn (they are designed to do this).
As said before, check the lip on the discs. If it's fairly pronounced you will probably want to replace them.
A warped disk will manifest itself as a pronounced judder under braking.

Dogbreath · 22 Oct 2008 at 11:15

Toker said:
I wouldn't worry about warped brake discs, they are pretty much a myth. It's nigh on impossible to warp a disc.

This is the new internet brake myth, it's entirely possible to warp a disk. The point is that it's that juddering brakes can , and often are caused by other things including inconsistent disk surface.

Toker · 22 Oct 2008 at 11:20

the only people I know who have warped discs are people who were stupid enough to totally hammer on brakes constantly with cheap crappy discs before letting them bed.

If they have decent bedded in discs and don't drive like a complete tool, then if they tell me they've warped their discs, I'll tell them they're a liar.

Dogbreath · 22 Oct 2008 at 11:27

I must be a compulsive liar then as I had a rear disk on my MR2 that was badly warped (showed 30 thou run out on a lathe, which pretty much matched what I measured with it on the hub) and it was only about 6 months old. Had it skimmed and brakes were fine again.

Griffo · 22 Oct 2008 at 11:56

Firestar_3x said:
Problem with discs is they have a minimum operating thickness before they need changing, for example 25mm when new and 23mm is worn needing replacement.

Odds are its the rear pad squeelers letting you know the pads are done.

Don't let the dealer do the work they always charge a fortune for brake related fixes.

By 'squeelers' do you refer to a 'device' (or bit of stuff) that makes the noise to warn of wear? If so: nice

I won't be taking it to a Skoda dealer, what with my experience thus far being: pap. They charged me 300 odd to change front pads and discs when I got it (didn't pay for it in the end). I'm hoping correct pricing and rear discs would equal a lot less.

I shall be going to a VAG specialist just outside Reading I think.

Thanks for the advice all! The brakes are pretty decent on this car I believe, been on for ages, I shall check the lip in a minute and see what it's at.

Toker · 22 Oct 2008 at 15:19

Dogbreath said:
I must be a compulsive liar then as I had a rear disk on my MR2 that was badly warped (showed 30 thou run out on a lathe, which pretty much matched what I measured with it on the hub) and it was only about 6 months old. Had it skimmed and brakes were fine again.

and you're positive it was warped rather than uneven deposits or surface collapse causing the juddering?

I just found a pretty good article on it actually

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

Lopéz · 22 Oct 2008 at 17:25

Toker said:
the only people I know who have warped discs are people who were stupid enough to totally hammer on brakes constantly with cheap crappy discs before letting them bed.

If they have decent bedded in discs and don't drive like a complete tool, then if they tell me they've warped their discs, I'll tell them they're a liar.

Another liar here then. Braking surface of disc warped several years ago, Sierra estate.

Not new discs so I wasn't "stupid" enough to hammer cheap crappy discs before they have bedded.