Holy clunk Batman!

[MarkT]

Have you rotated the wheel forwards and backwards when car
is jacked up, sometimes the pads can move in the caliper and cause a
clunk. The pad binds on the disc and jumps in the caliper.

Hope you sort it

Mark

[Rusty]

Not a very successful test drive. The clunk is still there and the fact that it's on 1 side and not the other AND that I put the best top mount I had on that side makes me think it's something else too... it's perhaps a little less prominent and the fact that the mount came out in pieces would indicate that it was part of it!

I couldn't test the brakes, the bloody bomb wouldn't recharge so I'm a bit stuck till that sorts it. I've got a new servo to fit but that's more work

Properly, properly, properly P'd off tonight!

[MarkT]

Rusty/Andy
Post #31, I replaced everything possible - brake pad was jumping in the caliper.

Mark

[urS6Tom]

I'll tell you about my experience with warped discs because I'd read that stoptech article and believed it, until it was proved to be wrong in front of my eyes.

I've got AP Racing 6 pots on the front of my S6 and on my last track day the front right was juddering so badly that I couldn't continue driving and had to miss the last couple of hours of the day

Luckily, I found someone who knew a lot about this subject through experience working on touring car brake systems and he agreed to have a look at the problem for me. The first thing he did was to measure the disc thickness using accurate digital calipers, second was to measure disc run out using a dial gauge.

First observation was the discs were down to minimum thickness. Second observation was that front left was in within tolerance, but on the right the disc had warped enough to show a significant deflection on the gauge. This is only measured in tenths of a mm, but is enough to cause a big vibration, especially when the disc is hot.

So, new floating discs were ordered from AP (took me a while to get over the cost of these) and the calipers removed, stripped completely, all corrosion removed, pistons cleaned, all seals replaced. Fitted Endless pads at the same time. Cost a lot of money, took a lot of time but the result is awesome stopping power delivered very smoothly and satisfaction of knowing that everything has been done properly.

So, that stoptech article may seem to make sense, but discs do warp, especially when they're down to minimum thickness.

Tom

[4WheelDrifter]

When exactly and in what conditions does this clunk occur?
I had a clunk in the S3 a few weeks ago. Over big bumps it sounded like something heavy was loose and landing in the boot. It turned out to be a rear ARB mount bolt had come loose and escaped.

You can refurb' the mono's yourself. It's easy enough.

[Rusty]

Clunk happens when you change direction with a hard right turn, the clunk is on the LHS. I think it might be the lower ball joint as the other side was replaced for the MOT and it was replaced at the same time and is on the higher load side.

When I get the brake bomb to recharge, I'll test the brakes

Need to study the brake assist system and see what's up. It could be that the seals in the servo are weak when not under pressure. Hopefully sort it... I'm not sure if there'd a pressure valve / 1 way valve that could be blocked... symptom is that the predal judders when pressed and you can feel the PAS pump pulses through your foot. I got really annoyed with it earlier, tiredness is never a pacifier!

I'll jack it up again tomorrow and look at the lower ball joint.

As it doesn't happen exclusively under braking and I've rebuilt and checked the brakes, I'm happy that it's not that... for now.

It's alright though, I learned the old girl by lighting up all 4 wheels

[4WheelDrifter]

I had a clunk like that once, accompanied by the sensation of the car moving about a foot across the road each time I changed direction hard. It was a loose lower ball joint.

[driftin jo]

I'll tell you about my experience with warped discs because I'd read that stoptech article and believed it, until it was proved to be wrong in front of my eyes.

I've got AP Racing 6 pots on the front of my S6 and on my last track day the front right was juddering so badly that I couldn't continue driving and had to miss the last couple of hours of the day

Luckily, I found someone who knew a lot about this subject through experience working on touring car brake systems and he agreed to have a look at the problem for me. The first thing he did was to measure the disc thickness using accurate digital calipers, second was to measure disc run out using a dial gauge.

First observation was the discs were down to minimum thickness. Second observation was that front left was in within tolerance, but on the right the disc had warped enough to show a significant deflection on the gauge. This is only measured in tenths of a mm, but is enough to cause a big vibration, especially when the disc is hot.

So, new floating discs were ordered from AP (took me a while to get over the cost of these) and the calipers removed, stripped completely, all corrosion removed, pistons cleaned, all seals replaced. Fitted Endless pads at the same time. Cost a lot of money, took a lot of time but the result is awesome stopping power delivered very smoothly and satisfaction of knowing that everything has been done properly.

So, that stoptech article may seem to make sense, but discs do warp, especially when they're down to minimum thickness.

Tom

Just because you have read it does not mean you understand !!
Read the article again !!!!!
The guy who wrote the article has been involved in professional racing for over 40 years , works for stoptech and is an expert in braking !

There is nothing in the article that says you cant have varying thickness on a disc , this does not mean it is warped !!!
As you have floating discs it is virtually impossible to warp them, Cast iron is a very stable material and does not warp unless it is under uneven stress torque from the wheel bolts and as you discs float this cannot be the case, the discs do however have the capacity to form cementite UNEVENLY if you get hot spotting . This is the cause of the run out you measured on you gauge .

[driftin jo]

I would suggest to everyone to read all the articles on this page , all very good stuff.


http://www.stoptech.com/tech_info/te...e_papers.shtml

[Rusty]

Always so aggressive Jo! People are allowed to disagree with you, not neccessarily because they're right or you're wrong...

Managed to solve the clunk using a pry bar! I need to get a nice big one for future 'investigations' Rear wishbone bolt was not tight, resulting in some movement on the rear and the bolt turned easily with a spanner but wasn't obviously loose. Those nuts are beyond annoying to get a non-swan-neck spanner on and that's assuming that you can get on the bolt... Set of swan neck spanners coming my way today then!

Hydraulic system was drained as much as I could (0.5 litres so 50% maybe) and refilled with new fluid. Thinking was that any debris in the sytem or fluid wasn't going to help my cause. Left it running for a bit and it's recharged nicely. Phew! New servo will have to be done though.

So, just he brakes left. They still judder a little but then they'll have worn a little with the judder so that's not a suprise, see if it resolves itself with some testing. There was corrosion on the hub and disc so I think that was to blame. Braking was strong and straight from up to 90 in the wet (the Michelin Primacy HPs gave good grip in nasty conditions). I have some spare pads I can try too. The DS2500s were in good condition, no damage or cracks.

So, pretty much there...

[urS6Tom]

Just because you have read it does not mean you understand !!
Read the article again !!!!!
The guy who wrote the article has been involved in professional racing for over 40 years , works for stoptech and is an expert in braking !

There is nothing in the article that says you cant have varying thickness on a disc , this does not mean it is warped !!!
As you have floating discs it is virtually impossible to warp them, Cast iron is a very stable material and does not warp unless it is under uneven stress torque from the wheel bolts and as you discs float this cannot be the case, the discs do however have the capacity to form cementite UNEVENLY if you get hot spotting . This is the cause of the run out you measured on you gauge .

Haha, not everything you read on the internet is true you know

The discs that warped weren't floating - the replacements are floating.

If you measure with calipers AND a dial gauge you can prove whether something is warped or not... but then I guess it all depends on your definition of 'warped'. Cementite/pad material build up is visible. If you're measuring on clean shiny metal you can rule this out as a cause.

Anyway, back to the thread - the important thing here is that it's fairly easy (and cheap) to establish whether your judder problem is being caused by the discs.

[Lloyd]

I have posted this several times but people still think they just by running a little hot on the track that they have managed to warp 10Kg of cast metal when they are actually just imprinting.

The standard brake bedding-in procedure will normall cure imprinting shudder, but if you truely have a vibration, look somewhere else (wheels, tyres, bearings etc)

Cheers n

Si

[driftin jo]

Haha, not everything you read on the internet is true you know

The discs that warped weren't floating - the replacements are floating.

If you measure with calipers AND a dial gauge you can prove whether something is warped or not... but then I guess it all depends on your definition of 'warped'. Cementite/pad material build up is visible. If you're measuring on clean shiny metal you can rule this out as a cause.

Anyway, back to the thread - the important thing here is that it's fairly easy (and cheap) to establish whether your judder problem is being caused by the discs.

"and an untold number of discs with pad material unevenly deposited on the friction surfaces - sometimes visible and more often not. "

[driftin jo]

[QUOTE=Rusty;528810]Always so aggressive Jo! People are allowed to disagree with you, not neccessarily because they're right or you're wrong...


This isn't about disagreeing with me though is it , it's about disagreeing with an expert in the field of braking with more than 40 years experience in professional racing . I'm not an expert in braking but I am an engineer with 23+ years experience in mechanical production environment .I have spoken with many engineers over the years who are experts in there particular field in engineering and thus learned a great deal how things work . When I read a white paper or speak to someone who has been at the top of there game for longer than I have I tend to take note. The thing that really gets me about the post I replied to is that the first statement was that the stopteck article was 'it was proved to be wrong in front of his eyes' . Nothing that was shown to this guy proves anything wrong with what is wrote in the article at all and the fact that he thinks it does proves that he has very little understanding of anything contained within it.


Sorry if I sound a bit pissed off sometimes but I have just spent an hour trying to explain to a blockhead manager at my work why me altering the feeds and speeds for machining a casting we are doing will not reduce the amount of inclusions we find in them ! I just wanted to say to him, feckin numpty for ****s sake **** off and go and educate yourself and stop coming to me with this ******** . Obviously I couldn't say that to him so there is some tension built up in me . The place I work at the moment has made a lot of jobs for the boys , managers jobs for friends of directors who know next to nothing about engineering , very frustrating sometimes , I come on here for I chill and it's happening here as well arrrrrrrrrrrr.
Seriously though peace out brother.

[urS6Tom]

"and an untold number of discs with pad material unevenly deposited on the friction surfaces - sometimes visible and more often not. "

amazing! so how does this guy know there is pad material on the surface of the disc if he can't actually see it?! has he got some kind of portable mass spectrometer!?

i still maintain that if you take a point on the disc (for argument's sake the OD) and it measures the same thickness all the way round on the calipers, but on the dial gauge it shows a deflection, then you have a warped disc.