Can you Skim Wave Discs?

[fast-ferret]

Hey all, I have an S4 but the previous owner upgraded to RS4 (or 5, I can't recall - I think they're the same) brakes, i.e. the ones with the wavy edge. It's come time to change pads and I don't fancy spending £700 on new discs as well so wanted to skim them (never been done before so they should have plenty of material in order to do so), for which I'd go to one of the pro cut lathe centres to have the on-car skimming. Problem is, I'm not sure the lathe would cope with a wavy edge disc.

Has anyone had one skimmed before?

 

[no_idea]

Hey all, I have an S4 but the previous owner upgraded to RS4 (or 5, I can't recall - I think they're the same) brakes, i.e. the ones with the wavy edge. It's come time to change pads and I don't fancy spending £700 on new discs as well so wanted to skim them (never been done before so they should have plenty of material in order to do so), for which I'd go to one of the pro cut lathe centres to have the on-car skimming. Problem is, I'm not sure the lathe would cope with a wavy edge disc.

Has anyone had one skimmed before?

Have you actually measured the thickness? The RS4 discs only have a 2mm wear allowance.
I replaced my discs and pads at 30k.

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[fast-ferret]

I haven't actually, I will check them later. Hopefully they're within tolerance otherwise it's an expensive game when it comes to brake pad change time!

 

[fast-ferret]

Have you actually measured the thickness? The RS4 discs only have a 2mm wear allowance.
I replaced my discs and pads at 30k.

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Just done a very quick rainy in-the-dark measurement and they’re coming up as 11.15mm - don’t suppose you know the minimum thickness do you? otherwise it’s an Internet hunt..


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[fast-ferret]

Just done a very quick rainy in-the-dark measurement and they’re coming up as 11.15mm - don’t suppose you know the minimum thickness do you? otherwise it’s an Internet hunt..


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That’s one side obviously, not the whole lot. Might be the wrong way to measure!


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[no_idea]

Front discs start at 34mm and minimum thickness is 32mm or 32.4mm, I can't remember off the top of my head. It is on the disc bell.
I can check tomorrow if you want?
Not sure what thickness you have measured?

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[no_idea]

That’s one side obviously, not the whole lot. Might be the wrong way to measure!


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Ah I see, you need to measure the total thickness.

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[fast-ferret]

Front discs start at 34mm and minimum thickness is 32mm or 32.4mm, I can't remember off the top of my head. It is on the disc bell.
I can check tomorrow if you want?
Not sure what thickness you have measured?

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Yeh I only did one side, I.e one side of where the cooling veins where. I was distracted I shall measure them correctly tomorrow morning.


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[fast-ferret]

Ah I see, you need to measure the total thickness.

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Couldn’t see the measurement on the disc for min thickness but mine seem to be 33.3mm, maybe a smidge over.


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[no_idea]

Couldn’t see the measurement on the disc for min thickness but mine seem to be 33.3mm, maybe a smidge over.


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It's on the disc bell, but if they have turned black and are covered in crud you may not see it.
If they are that thickness you will get away with a skim, but to be honest unless they are heavily scored I would leave them as you are only taking away precious material. Maybe take the lip off, if there is one.

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[fast-ferret]

It's on the disc bell, but if they have turned black and are covered in crud you may not see it.
If they are that thickness you will get away with a skim, but to be honest unless they are heavily scored I would leave them as you are only taking away precious material. Maybe take the lip off, if there is one.

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I never know really what to do with discs. People say do discs and pads at once but do people really replace discs that cost £700 after one set of pads? That seems madness.


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[RAF_S7]

In my 35+ years of car ownership, I’ve never had to skim disc’s for a pad change.

Are yours that bad? Pictures?

 

[fast-ferret]

In my 35+ years of car ownership, I’ve never had to skim disc’s for a pad change.

Are yours that bad? Pictures?

I’m not doing it because I think they look bad to me but rather because the advice seems to be to always replace discs and pads at the same time, and I’d rather not spend £700 of new discs if I can avoid it.


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[RAF_S7]

Unless your discs are corroded, or below manufacturers recommended minimum thickness, I’d just change the pads.
The main thing with fitting new pads on “used” discs is that there is a bedding in period before full braking efficiency is reached.

Save the £700.....

 

[cosmicblue]

My recently departed RSQ3 had the wavy discs too, the 2mm (basically 1mm each side) wear limit is crazy. Crewe Audi did a deal and I think I paid £450 for a pair. I fitted EBC RedStuff pads which worked better (more bite), were easy on the discs (negligible wear - just polishes them like mirrors) and produced very little dust once bedded in. EBC will have pads for my B9 RS4 in around 6 months - it will be getting a set for sure.

 

[fast-ferret]

My recently departed RSQ3 had the wavy discs too, the 2mm (basically 1mm each side) wear limit is crazy. Crewe Audi did a deal and I think I paid £450 for a pair. I fitted EBC RedStuff pads which worked better (more bite), were easy on the discs (negligible wear - just polishes them like mirrors) and produced very little dust once bedded in. EBC will have pads for my B9 RS4 in around 6 months - it will be getting a set for sure.

Yeh it does seem a bit mad to me, although I’m not familiar with how much wear allowance other discs have to be honest so I’ve nothing to compare it to.

That price is very good, what magic words did you have to say for that?

A related question, any idea who makes the discs? Presumably not Audi themselves, perhaps if we knew the OEM we could buy direct - for the suspension on my S4 I bought Lemforder parts and they’re the exact same parts with the Audi logo ground off, and about 1/3 the price...


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[cosmicblue]

The pair I removed are under the bench in my garage - you can have them if you want, I changed them at 30,000 miles on the RSQ3, they would still be serviceable if you used EBC pads (won't wear any more of the surface away). I'm in Warwick...you can have them for free if you can pick them up.