Car wobbling when braking

[Benish7]

Hi, I have a A6 Avant and at high speed when I gently press the brake the car wobbles/shakes.
It doesn’t do it if I press the brakes hard, and it doesn’t tend to do it until I’ve been in the car a while (20+minutes).

It did it this evening around 60mph and I didn’t feel it doing it much below that speed
In comparison the other day it tended to do it at all speeds but again only after a certain time and only started once I was above 60ish.

Nothing at all is felt through the brake pedal or the steering wheel.


Any suggestions? Warped discs?

Thanks for you’re helping

[Roverfan]

I'd check for damaged tyre sidewall first, a cut or missing a (small) chunk.

[morski]

Yep,, discs are on their way out. Get them the thickness checked and if its close to the minimum then get them changed along with the pads

[Benish7]

I'd check for damaged tyre sidewall first, a cut or missing a (small) chunk.

Thanks I’ll take a look.

Yep,, discs are on their way out. Get them the thickness checked and if its close to the minimum then get them changed along with the pads

Do you reckon it’s the rears?
Any explanation to why this seems to only occur after a period of driving? I’m assuming it’s once heat has built up but surely if they are warped it should be occurring all the time?

[Crasher]

Have the disc runout checked.

[morski]

Could be a combination of anything, slightly warped discs, worn discs, worn pads, sticking piston on a caliper? Need to get them measured and checked for run out

[bluezie]

As said above, and buckled wheel (very easily done if running 20 inch), bent hub, and damaged or badly manufactured tyre.
Also worth checking the shock absorbers, as a dud one will cause wheel bounce at certain speeds, especially if something is out of balance, as it will hit resonant frequencies, which will change as the tyres and shocks warm up.

[Benish7]

I’m guessing as it’s only occurring whilst braking it won’t be a buckled wheel or tyre issue?!


Anyway, I had a guy I know put it on the rolling road down at his garage and he said the rear discs and pads need changing so I went and got the parts and did it yesterday.
Unfortunately the issue remains 🤬😤😔

[bluezie]

I’m guessing as it’s only occurring whilst braking it won’t be a buckled wheel or tyre issue?!

Not always - I've had a bent hub on an A6C5 that only vibrated when hard braking, and only last week had 2 new tyres on my van, and finally the shaking between 30mph and 60 mph has gone, the weird thing with this, is the shaking only happened during hard acceleration, and it had been like it for 2 years.
Tyres can be guilty of all sorts of odd behaviour, I've even had a couple that sounded like a knackered wheel bearing, i.e. howls and moans.
It may be worth swapping each wheel for the spare and see if it goes away....

[Crasher]

When we have an issue like this we always runout check the hubs before fitting new discs, it is no use fitting new discs to a warped hub. The spec is 0.03mm and we measure both sides of the bolt hole.