Update on my Warped Discs

[S.Speed]

I'm suprised you spoke with the mechanic! The usual gripe with MB dealers is you can never get past the service team leader. I definately would have asked to speak with the set ice manager.
As posted above the. Orrect action should have to return the discs for inspection and sold you some replacements on the understanding if faulty you get a refund for both sets.

Initially when I went into the dealership it was one of the receptionists who spoke to me..
Then when things got technical a male collegue from another desk joined in and then after a few minutes the mechanic who took the car for a test drive turned up...
So there was "little old me" facing three of MB's finest

On a serious note though, I re iterate that for the DIY maintenance people out there, there is no point in going to MB for parts when you have no come back when parts they sell fail.
I am absolutely serious about using quality parts sourced from elsewhere.
I know they dont give 2 hoots about me or my discs...
In the scheme of world problems its neither here nor there...

One last comment that the mechanic did make..
He said the discs were unusually smooth and shiny and that they looked as new...
I told him that was because Green Stuff pads dont rely on fragments of metal for friction and that makes them much kinder on the discs..
He didnt comment after this last exchange..

 

[cleverdicky]

Have you measured by how much they have warped ?

 

[S.Speed]

Hi,
No I haven't measured the run out. ( though I do have a dial gauge).
The mechanic did agree they were warped after his initial inspection.
To be honest I shall just replace them soon. I'm not that concerned about the measurements.

 

[television]

Cast iron is a very unstable metal at the best of times, and many things can happen. wear for instance could just relieve a tension spot and allow it to change shape. Heat is the other thing, some disc fail after a hard stop, just the few seconds that most hold the brake pedal pushed can be enough after the stop.

In the days when we had cast iron cylinder heads, if you ran out of water and boiled the engine, the head would warp.

Welding the stuff requires very special pre heating

 

[Frontstep]

We are, as in life a disparate lot on here,
the consensus though points towards an examination of the parts, a compromise agreement to keep the vehicle on the road and a pre agreed set of procedures pending results.
It seems so unnecessarry to have dispute, the problem is the people you spoke to don't have a "big picture" mentality why,
are you born with it, do you learn it ?
I certainly agree with the twitter comment though, I have never been near it but the immediacy and reach of posts are enticing.

 

[hotrodder]

Hi,
No I haven't measured the run out. ( though I do have a dial gauge).
The mechanic did agree they were warped after his initial inspection.
To be honest I shall just replace them soon. I'm not that concerned about the measurements.

So you didn't measure the run out when fitting them?
All this talk of 'warped' discs... do we mean warped as in physically bent akin to a bicycle wheel or is everyone using it to describe 'disc thickness variation' (DTV) which is the usual suspect for brake judder?

I could buy the unstable cast iron story if we were talking about the cheapest aftermarket rotors that were available from a motor factors budget/economy line. There are MANY flavours of cast iron and there are SAE specs* for the alloys used in the production of brake rotors along with the stress relief heat treatments that should be part of the production process.

Having said that a rotor 'buckling' by say 0.01mm would be less noticable than a thickness variation of 0.01mm due to the way hydraulics work. If the new disc has excessive run out when fitted (and a general ball park maximum run out is typically 0.1mm) then things will work fine initially but as one spot is constantly rubbing the pad it'll wear ever so slightly more than the rest of the disc. After a few thousand miles this thickness variation (while miniscule) will begin to be noticable through the brake pedal.

Probably not relevant here but brakes don't work solely on abrasive friction between pad and rotor. Adherent friction also plays a role in that a very thin layer of pad material is deposited on the disc at higher temps which is continually being replaced. Uneven pad deposits can also cause thickness variation, say a high speed stop followed by sitting stationary with a foot on the brake. One of the reasons why it's recommended to avoid hard use of new rotors, especially immediately stopping and keeping the brakes applied is that why a 'pad imprint' can be a temporary the heat soak can alter the microstructure of the iron rotor resulting in a hard spot that wears at a different rate leading to... thickness variation and judder

Not excusing or defending the nonsense spouted by the dealer but look at it from their (or any motor factors) POV... punter buys some new rotors, a few months/several thousand miles go by and then he's back complaining of brake judder. In their position the first thing i'd ask is 'did you measure the run out when you fitted them'. I'd wager that a blank stare is probably a LOT more common than 'yes' and a fair bit more common than something like 'no, but i carefully cleaned the hub/rotor mounting face of dirt/grit/rust/burrs'.

MB have a spec for the acceptable runout of wheel hubs and probably have one for rotors too. Pretty much every brake manufacturer has articles on their site about DTV, disc run out etc. If you don't measure it how can you be sure it's the discs fault and not the hub/something between the hub and rotor?


* A paper on the metallurgy of grey cast iron for brake rotors for those that are interested in, err, metallurgy... http://www.sae.org/events/bce/tutorial-ihm.pdf

 

[television]

I would agree that a thickness change is more noticeable the run out, and probably a better name for it.

I recently changed my front V70R disc, they changed in thickness, but very odd, they could be ok for a few weeks then really bad, then revert back again.

They were bad at the last MOT and my friend would not pass them, so new disc it was, they only cost £10 each so no big deal

 

[creepy coupe]

Hate to sound like a smart ares. but I had a feeling it would go that way, given the pads were not MB. For them it was like someone had thrown them a lifeline.

Pity about that

 

[EuroCarParts]

Hate to sound like a smart ares. but I had a feeling it would go that way, given the pads were not MB. For them it was like someone had thrown them a lifeline.

Pity about that

True

If they were Pagid / ATE / TEXTAR etc, then you can stand and argue all day that they are Block Exempt [therefore MB cant discriminate against them]
However i'm not 100% on Green Stuff, so i wouldn't feel confident arguing

They were bad at the last MOT and my friend would not pass them, so new disc it was, they only cost £10 each so no big deal

£10 Each! WOW

 

[turbopete]

So you didn't measure the run out when fitting them?
All this talk of 'warped' discs... do we mean warped as in physically bent akin to a bicycle wheel or is everyone using it to describe 'disc thickness variation' (DTV) which is the usual suspect for brake judder?

I could buy the unstable cast iron story if we were talking about the cheapest aftermarket rotors that were available from a motor factors budget/economy line. There are MANY flavours of cast iron and there are SAE specs* for the alloys used in the production of brake rotors along with the stress relief heat treatments that should be part of the production process.

Having said that a rotor 'buckling' by say 0.01mm would be less noticable than a thickness variation of 0.01mm due to the way hydraulics work. If the new disc has excessive run out when fitted (and a general ball park maximum run out is typically 0.1mm) then things will work fine initially but as one spot is constantly rubbing the pad it'll wear ever so slightly more than the rest of the disc. After a few thousand miles this thickness variation (while miniscule) will begin to be noticable through the brake pedal.

Probably not relevant here but brakes don't work solely on abrasive friction between pad and rotor. Adherent friction also plays a role in that a very thin layer of pad material is deposited on the disc at higher temps which is continually being replaced. Uneven pad deposits can also cause thickness variation, say a high speed stop followed by sitting stationary with a foot on the brake. One of the reasons why it's recommended to avoid hard use of new rotors, especially immediately stopping and keeping the brakes applied is that why a 'pad imprint' can be a temporary the heat soak can alter the microstructure of the iron rotor resulting in a hard spot that wears at a different rate leading to... thickness variation and judder

Not excusing or defending the nonsense spouted by the dealer but look at it from their (or any motor factors) POV... punter buys some new rotors, a few months/several thousand miles go by and then he's back complaining of brake judder. In their position the first thing i'd ask is 'did you measure the run out when you fitted them'. I'd wager that a blank stare is probably a LOT more common than 'yes' and a fair bit more common than something like 'no, but i carefully cleaned the hub/rotor mounting face of dirt/grit/rust/burrs'.

MB have a spec for the acceptable runout of wheel hubs and probably have one for rotors too. Pretty much every brake manufacturer has articles on their site about DTV, disc run out etc. If you don't measure it how can you be sure it's the discs fault and not the hub/something between the hub and rotor?


* A paper on the metallurgy of grey cast iron for brake rotors for those that are interested in, err, metallurgy... http://www.sae.org/events/bce/tutorial-ihm.pdf

the problem is, though, MB wouldnt have measured the run out of new discs when theyre fitted! they just fit them, go for a drive, if problem cleared, great! if not, look deeper into the problem. ALL garages, to the best of my knowledge do it this way. many garages ive been in/worked at etc dont even bother to clean up the hub face as it would take up time and reduce their profits/staff bonus!

 

[television]

True




£10 Each! WOW

I bought them in Sweden, the V70's over there are like flies. I bought them back in my suitcase, it was a little over weight. In fact the girl on the checkout wanted to charge me excess baggage till I asked if the lady behind me had paid twice as much for her ticket as me and she was at least twice my weight, they let me go through free

 

[carloss]

Well that sucks :/

There are many dealers who would of brushed it off and supported you, however some will take it to the extreme (fitting 'performance' pads' your self gives them an argument, but there should never be an argument!)

It seems you've got the right attitude - walk away and not shop at that dealer again. Their loss!

True

If they were Pagid / ATE / TEXTAR etc, then you can stand and argue all day that they are Block Exempt [therefore MB cant discriminate against them]
However i'm not 100% on Green Stuff, so i wouldn't feel confident arguing

So what would eurocarparts do in the same situation?? and out of interest what is the return rate of the parts your company supplies to what you call "the price sensitive range"

 

[hotrodder]

the problem is, though, MB wouldnt have measured the run out of new discs when theyre fitted! they just fit them, go for a drive, if problem cleared, great! if not, look deeper into the problem. ALL garages, to the best of my knowledge do it this way. many garages ive been in/worked at etc dont even bother to clean up the hub face as it would take up time and reduce their profits/staff bonus!

Yeah but if you're paying a garage to fit the discs and pads they can't accuse you of fitting them wrongly and/or using incompatible pads which is what's happened to the OP.

 

[turbopete]

Yeah but if you're paying a garage to fit the discs and pads they can't accuse you of fitting them wrongly and/or using incompatible pads which is what's happened to the OP.

true, but what about the people who are qualified but either work for themselves or currently dont work in a garage, like myself? i must admit, id be reluctant to pay the premium to buy from MB after reading this thread!

 

[cleverdicky]

how many sets of discs and pads would just one hour of MB workshop time buy I wonder ?

 

[carloss]

Yeah but if you're paying a garage to fit the discs and pads they can't accuse you of fitting them wrongly and/or using incompatible pads which is what's happened to the OP.

To try and bring the situation into context if i sold you (for arguments sake a leather suite) and you cleaned the said suite with a product not endorsed by me and it destroyed the leather who would be liable???

 

[television]

To try and bring the situation into context if i sold you (for arguments sake a leather suite) and you cleaned the said suite with a product not endorsed by me and it destroyed the leather who would be liable???

Not the same thing is it, nothing wrong with the green pads as used all over the world, there are no laws in existence as anyone can change service items.

As Simon said green pads are kinder to the disc

 

[carloss]

As Simon said green pads are kinder to the disc

OK malcolm where is the proof to the above statement also how can a MORE efficient brake pad fullfill the above quote

If the op had used approved merc pads this thread would not exist

 

[television]

OK malcolm where is the proof to the above statement also how can a MORE efficient brake pad fullfill the above quote

If the op had used approved merc pads this thread would not exist

Alfie, I suggest that you read up on EBC products, I am not in the mood for ab argument so over and out

 

[Naraic]

OK malcolm where is the proof to the above statement also how can a MORE efficient brake pad fullfill the above quote

If the op had used approved merc pads this thread would not exist

That may be so...but does that mean MB are right?