My 1998 A4 (30v 2.8), 80K miles, has had a rattling sound since I've owned the car (almost a year) from the left front suspension while driving slowly over semi-rough pavement (old deteriorating concrete parking lot and driveway), but steering and suspension still feels nice and tight while driving over smooth roads, no handling problems at all.

About a week ago, I started experiencing a "thump-thump-thump" continuous kind of vibration from the front left wheel, but only when braking moderate or hard. It's worse the harder I press the brake pedal, and I'm starting to feel it in the steering wheel while braking too, plus I feel the thumping feedback thru the brake pedal as well. It feels like the whole left wheel and suspension assembly may be bouncing fore and aft while under braking. When it first started, I thought I might have a warped brake rotor, but it looks visually fine.

There is no metallic knocking at all, it feels more like some kind of large rubber bushing type of component has failed, since the thumping is more "smooth" as opposed to "hard" feeling.

Any ideas which suspension component is most likely failed?

Control arm bushings? (steering is still tight and smooth on smooth roads however)

Front strut/shock bushings?

 

Could be any number of things: TRE's, control arm bushings, brakes, wheel bearings, CV joints, etc...

First thing I would do is put the car in gear, parking brake on, and jack up the driver's side front. Grab the wheel at 3 o'clock and 9 o'clock and try to wiggle it. Push it away from you, pull it towards you, try to turn it like a steering wheel and turn it the same way it would turn if you were driving and actually turned the wheel in the car. Then grab the wheel at 6 o'clock and 12 o'clock and repeat the same tests. One of those movements should reproduce the clunk you're hearing and allow you to track it down.

The thudding you feel in the brake pedal makes me think warped rotor(s), so you might check that out too.

 

i chuckled at this. theres no way you are going to see a warped rotor. and by the way, i got a $10 bill that says this is the cause of your thumping issue, which is almost enough to buy a new rotor. don't get it turned. just buy a new one.

 

I agree 100% and just had this very problem with my 'non-audi' vehicle - pedal was kicking back at me. replace rotors and it went away.

 

Well, the new rotors and pads fixed the brake thumping. It stops very smooth now. The inside surface of the left rotor was visibly showing signs of irregular wear patterns once it was removed and in bright light where I could get a good look at it.

On a more depressing note, I got a good look at the control arm bushings, and they're all dried out, worn and cracking too... so I need to replace them all, and the front wheel bearings are worn, and the outer axle boots are broken too.... so it looks like I need to spend some more money on the front suspension soon.

I'll replace all the control arms, tie rod ends, sway bar coupling ends, wheel bearings, drive axle boots, and probably should replace the shocks too while I'm at it. The car has almost 85K miles on it, so I might as well replace every wear item...basically every moving part in the whole front end while I'm at it since the labor savings will cost-justify rebuilding the whole front suspension if it's all done at once. That should make it drive like a new car when done.

 

Don't feel bad, I am in the same boat but I think my issues arrose from me not getting my ABS problem fixed. Now I am going with new CV's, new wheel bearings, rotors, pads, tie rods. I am just going to have to find the time to do it

:^(