problem with vibration when braking

[noogman]

Hi all.

I have some problem with vibration when braking from high speed. When driving in the city all looks fine. However when driving around 90mph and start braking brake pedal starts vibrating till around 50 mph(steering wheel too but not as much as pedal). Below 50mph there is no vibration or is impossible to feel.

Does any body know what can be a reason of it. Someone said to me that brake discs maybe out of shape or about to end. If yes which one front or rear? Week ago was changing front tyres and when tyres were taken out of axle I was trying to turn the discs around. It was possible however very hard. Today was changing rear tyres and I could have turned rear disc much more easier then front one. Does it mean that front one are out of shape.

Or maybe something completely different. Do you have any idea. Just to mention that camber and alignment is done and is correct?

Thank you for any help

[Guest 2]

how many miles on the car? it sounds like brake judder which would suggest your discs need changing.

[AtotheK]

Sounds like the front discs are coming to end of their life. Obviously they bare the brunt of braking heft so it follows that they may go first.
I had the same symptom on my 2007 A6 which did indeed turn out to be discs...
I hope this helps. A


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[noogman]

Car has 93000 on the clock. Front one are new changed around 30k miles ago and there is no sharp edge on the inner side. But the rears have the sharp edge already and when I look at them I can see brownish colour (hope you know what I mean) and probably are from new. Some one said to me that rear brakes do not work with full power on low speed and start working fully on high speed. I could explain reason why it vibrates on high speed not on low speed. Am I correct?

[AtotheK]

If your fronts are only 30k old and the tears 93k then that suggests rears. I should have asked the obvious questions Chris did instead of jumping to conclusions... My bad!
But in any case the symptom does point to discs.


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[noogman]

Someone also said to me that it could be wishbone. Hope not as more expensive. What do you think?

[AtotheK]

Can't see why a wishbone would only vibrate as you describe it. I would have thought it would be a more constant problem as it is a suspension component that is in use constantly and that it might also show an affect when manouvering/turning etc.
But excuse me, I'm no mechanic/expert in this matter. It's just that what you describe sounds very like what I encountered shortly before my discs went...
Nothing for it but to hit up your local dealer, they'll surely investigate it for you and most likely for free (at least they do if they're Robinsons Audi of Norwich...)


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[noogman]

thank you. Will start from rear discs. Will see what garage say tomorrow.

[A6S]

Poorly balanced tyre is most likely your cause of it happens at speed and not slow

[AtotheK]

But only when braking? Not sure. Again that would cause more constant vibration I would have thought?


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[noogman]

As I mentioned before. Two weeks ago I have changed front tyres and it was vibrating before and still is.. How to check if this is are brakes and which one front or rear?

Thanks

[micheal balbrig]

If you have to fit new front pads and discs,ensure that the mating hubs are cleaned spotlessly before fitting new discs,or you may have to repeat job in a short time.
Check for wear in front suspension before fitting brake units
It seems from what you describe more likely to be front brakes or suspension problem

[noogman]

Wheels are fully balanced as I changed them two weeks ago and today. Vibration was before change and after.

[A6S]

Likely a bush or a ball joint if it was happening before your new tyres.

[Jackblack]

Brake discs 100%. Even at 30 k after fitting the new discs if you travel on motorway and are driving at 90 mph and reduce to 40 -50 mph rapidly and then return to 90 mph the metal on the discs unless they are OEM ( original Audi ones) are prone to warping. If this is part of your driving behaviour and is repeated then the discs will not survive without warping. In basics the discs heat up very quickly and get extremely hot and then cool quite rapidly as you simply continue on your motorway journey resulting in deformation and warping. Happened to me years ago so i have practical experience.

I also have a friend that had an RS4 who took it to a track and same conditions high speed rapid braking + super tempratures and then rapid cooling as it went onto the next straight. Discs become warped. He went to Audi and told them the brakes were vibrating. Audi inspected the brakes and could see the tell tales signs of overheating of metal and the told him to "P" off saying to him you've been racing this thing !!


Heat tint colour chart

The table below represents the temper colours that are likely to form on stainless steel type 1.4301 (AISI 304) if heated in air.
THIS INFORMATION MUST BE USED WITH CARE WHEN INTREPETING THE HINT TINT COLOURS OBSERVED ON STAINLESS STEEL SURFACES AS THE HEATING CONDITIONS ARE NOT SPECIFIED.


Colour Formed
Approx Temperature C


pale yellow
290


straw yellow
340


dark yellow
370


brown
390


purple brown
420


dark purple
450


blue
540


dark blue
600

[pmartin35]

Sounds like the discs too me, when they get excessively worn they can warp and cause a judder under braking, if it's felt through the steering wheel as apposed to the body of the car it's more than likely the front discs


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[Bar Shaker]

The most likely cause of this is if you park outside and are getting a film of rust on the discs. The area behind the pads doesn't rust and you end up with very slight differences in the thickness of the discs, once the rust has been wiped off. It should go after a couple of big breaking actions as the pads will re-face the discs.

If it doesn't go, you can get the discs re-faced with a grinding machine. The wheels need to come off but the machine does the discs with them still on the car. If they are OE discs and are otherwise perfect, it's worth trying this before replacing them.