Discs & Pads Questions??

[t_urbo]

Rs4v8

Remember the Doctor in Cannonball Run (Jack Elam), do you have his eyes?

Just trying to build a pic here.

[rs4v8]

LOL... it's interesting I must admit years ago on a mk2 golf GTI I had to change the discs and they were warped so badly the whole car shook..... after i changed them it was fine under breaking and normal driving. I guess under intense heat etc metal does change shape does it not?? I'm not saying I don't believe your point of view just not totally conviened that it is sceintifically impossible for discs to warp.

It is most certainly possible to alter the metallurgical structure (and therefore shape) of metal using heat. brake discs are well capable of heating up enough to do this during hard braking and potentially rapid cooling (if there's any water around) will make it worse. Brake discs are made with this in mind but only to a certain level. Very hard use, such as on a track, is very likely to put them in a situation for which they have not been designed and so may cause them to do unexpected things..

right, any pictures anyone??

[rs4v8]

Rs4v8

Remember the Doctor in Cannonball Run (Jack Elam), do you have his eyes?

Just trying to build a pic here.

Nah, no glasses, here's a photo of me!!

[alex_123_fra]

I got nowhere near the price a couple of you mentioned. The retail price for just the discs was £285.10 each plus VAT, then £207.73 plus VAT for the pads.

Total bill at retail money including fitting, VAT plus a brake fluid change (made sense to get the fluid done given pads & discs were being replaced), was £1095.35. I did manage to get a dealer credit of £500 so i paid just shy of £600. Still, without the credit i was looking at £1100 for the entire job.

Car feels much better now on the brakes & the discs were in fact slightly warped, scored on the back & generally uneven which the Master Tech rightly said was heat related.

Glad it's all sorted, but i'd love to know how a price of under £700 is possible for front pads & discs, given just the discs are over £600 without VAT & no fitting??

Paul, that is quite steep in all honesty but whats done is done. If I remember correctly, DSGwagen were doing the front discs for approx. £280 (inc VAT) and front pads for approx £180 (inc VAT). I know I paid approx £850 but that was for a set of front discs, front AND rear pads.

Labour to fit the front discs and pads was 60-70 quid (1.5 hours) and my rears did not need changing yet so I've just kept them as spares.

[alex_123_fra]

Rs4v8

Remember the Doctor in Cannonball Run (Jack Elam), do you have his eyes?

Just trying to build a pic here.

Nah, no glasses, here's a photo of me!!

Ugly fecker ain't ya

[rAudiguy]

right, any pictures anyone??

what flavour did you want???

[rs4v8]

alex123 raudiguy That's another rib gone!!!

[t_urbo]

LOL... it's interesting I must admit years ago on a mk2 golf GTI I had to change the discs and they were warped so badly the whole car shook..... after i changed them it was fine under breaking and normal driving. I guess under intense heat etc metal does change shape does it not?? I'm not saying I don't believe your point of view just not totally conviened that it is sceintifically impossible for discs to warp.

If the discs are mounted properly they will not warp, so with regard to this thread the said vehicle was new so its safe to say they were mounted properly.

It only takes a 0-1mm difference in surface thickness to be felt through the brake pedal, so im amazed how the Human eye can see such a small difference in tolerance.

I pulled this from another site, but it has to be said any decent racing team/company will say the same, however you will find dopey dealers, brake distributers,parts companies and some mechanics use the term warped on a regular basis.

The overwhelming cause of brake judder is a condition called Disc Thickness Variation – period! In other words the disc develops a lack of parallelism between its inboard and outboard friction surfaces. I say, “develops” because even discs that are
machined to the very tightest tolerances during production can easily develop Disc Thickness Variation (hereafter referred to as: DTV) due to incorrect fitment or driver abuse.
When the brake pads are pressed up against a disc that has developed DTV they will pass over a series of thinner and thicker areas on the braking surface of the disc in rapid succession. Considering that the brake pads are being pushed together with substantial force they will be forced down into the ‘cavities’ or thinner areas only to be kicked back violently when reaching the bumps or ‘thicker’ areas. The frequency of this
‘bouncing’ action is typically over 100 Hertz when braking from highway speeds of around 130kph. This results in pulses that are transmitted through the caliper pistons, via the brake fluid to the driver, who experiences them as brake judder..

[t_urbo]

Rs4v8

Remember the Doctor in Cannonball Run (Jack Elam), do you have his eyes?

Just trying to build a pic here.

Nah, no glasses, here's a photo of me!!

Yeah right, you pulled that photo out your wallet....

[rs4v8]

LOL... it's interesting I must admit years ago on a mk2 golf GTI I had to change the discs and they were warped so badly the whole car shook..... after i changed them it was fine under breaking and normal driving. I guess under intense heat etc metal does change shape does it not?? I'm not saying I don't believe your point of view just not totally conviened that it is sceintifically impossible for discs to warp.

If the discs are mounted properly they will not warp, so with regard to this thread the said vehicle was new so its safe to say they were mounted properly.

It only takes a 0-1mm difference in surface thickness to be felt through the brake pedal, so im amazed how the Human eye can see such a small difference in tolerance.

I pulled this from another site, but it has to be said any decent racing team/company will say the same, however you will find dopey dealers, brake distributers,parts companies and some mechanics use the term warped on a regular basis.

The overwhelming cause of brake judder is a condition called Disc Thickness Variation – period! In other words the disc develops a lack of parallelism between its inboard and outboard friction surfaces. I say, “develops” because even discs that are
machined to the very tightest tolerances during production can easily develop Disc Thickness Variation (hereafter referred to as: DTV) due to incorrect fitment or driver abuse.
When the brake pads are pressed up against a disc that has developed DTV they will pass over a series of thinner and thicker areas on the braking surface of the disc in rapid succession. Considering that the brake pads are being pushed together with substantial force they will be forced down into the ‘cavities’ or thinner areas only to be kicked back violently when reaching the bumps or ‘thicker’ areas. The frequency of this
‘bouncing’ action is typically over 100 Hertz when braking from highway speeds of around 130kph. This results in pulses that are transmitted through the caliper pistons, via the brake fluid to the driver, who experiences them as brake judder..

Your tv refresh rate is 50hz and you can't even see that, not sure how your leg would feel 100hz I do definately agree that you can feel something through the pedal when your discs are f**ked, no doubt. I can also see how the thickness would vary and that this may / will get worse over time. But I have seen discs which would not sit on a flat surface with out rocking. sorry but that is a fact..... not pringled though and I do concede this point!!

[s4woody]

i can do alot better than that..

The retail price for just the discs was £285.10 each plus VAT, then £207.73 plus VAT for the pads.

[W8PMC]

I got nowhere near the price a couple of you mentioned. The retail price for just the discs was £285.10 each plus VAT, then £207.73 plus VAT for the pads.

Total bill at retail money including fitting, VAT plus a brake fluid change (made sense to get the fluid done given pads & discs were being replaced), was £1095.35. I did manage to get a dealer credit of £500 so i paid just shy of £600. Still, without the credit i was looking at £1100 for the entire job.

Car feels much better now on the brakes & the discs were in fact slightly warped, scored on the back & generally uneven which the Master Tech rightly said was heat related.

Glad it's all sorted, but i'd love to know how a price of under £700 is possible for front pads & discs, given just the discs are over £600 without VAT & no fitting??

Glad you got a decent price, would love to see a pic of your 'WARPED' disc.

Is that what Audi 'mechanic's' call themselves these days, Master Tech'.
I wonder if a Master Tech would have the ability to strip and rebuild an engine?

No picture as i don't often take my camera to the dealers when i'm having work done.

However i did see the discs both on & off the car & the warp was only on the front disc aspect & no it looked nothing like a pringle.

To explain a tad more, the Master Tech (i think that's like a Senior RS Mechanic ) removed both discs & ran them on some machine (bit like a wheel balancer but smaller) & this identifies abnormalities on the disc surface/shape. Due to it being a tad out of shape, he could not get a true reading for the entire surface area, which also indicated the slight warp. The back of the disc was scored & the front was out of shape enough to cause the vibration, as well as some pad deposits (as you rightly said) welded onto areas of the disc surface.

Needless to say, i now have no vibration when braking & they feel much stronger. Given the wear sensor had disconnected (had it been connected it would have been lighting up the dash like an Xmas tree), my pads were right on the limit when replaced & the nearside was low enough to cause scoring on the back of the disc.