Front-end vibration

[Diablo]

I have a 2005/6 A8 3.0tdi. Recently, I have noticed the following:

When braking from 60mph+, moderate brake application result in a lot of vibration in the steering wheel and the front end generally. I think I can also feel the brake pedal pulsating a little.

When braking from 60mph+, heavy application of the brake pedal results in less vibration in the wheel and front end.

Slow speed braking is fine.

My mechanic changed the pads from Red Stuff (fitted by previous owner) with Pagid ones. It has not really made much of a difference. I suspected the discs, but the mechanic, who has not taken them off, reckons they are ok and that a wheel bearing may be worn.

I suspect that the front disc/discs are warped. Does anyone have any ideas??

Thanks in advance.

[Architex_mA8tey]

Sounds like either warped discs as you suspect or perhaps a sticking caliper otherwise. how old is the brake fluid also?

[Diablo]

Hi, I think that the brake fluid is less than 2 yers old, but I will need to confirm. If it is old, could that be linked to the vibration?

Thanks.

[PsYcHe]

I assume you get no vibration otherwise? But have you had the balance checked?

I'd suspect a disc with at least some embedded crap on it, if not actually warped.

[ainarssems]

If You feel it on pedal it's gotta be warped disc, otherwise could be suspension bushes

[Diablo]

Originally Posted by PsYcHe

I assume you get no vibration otherwise? But have you had the balance checked?

I'd suspect a disc with at least some embedded crap on it, if not actually warped.

No, no other vibrations.

[Diablo]

Originally Posted by ainarssems

If You feel it on pedal it's gotta be warped disc, otherwise could be suspension bushes

I know it sounds odd, but I cannot tell if the pedle itself is pulsating. On moderate pedal pressure, the vibration is so bad that it seems like the whole front end is vibrating...

If discs are shot, shouldn't it vibrate at all speeds?

[Conan_the_Librarian]

Given the variance of vibration and speeds I'm going to suggest a sticking caliper.

If they are single pot sliding calipers take your hands off the wheel when braking (in a safe place with plenty of room either side and no one else around). If you vear to one side that would indicate that one brake is less efficient than the other - Warped disk / sticking caliper.

If you have multi pot calipers then I sugest one pot in one caliper. Heavy braking at speed stops the vibration. Light braking has one pot forcing the brake disk onto the other pot causing heavy vibration.

One whole English penny on it!