problem with vibration when braking

[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.