Matt Pizzola

Ok this is driving me nuts...been looking through the forums but not finding my issue. Not saying it isn't there, but not finding it. Here's what I have:
Changed out all four upper control arms on my 2007 A8. Went with moog aftermarket super duty (or whatever they were called). New tires, new alignment. Have weird oscillation at speed. Most noticeable between 40 to 50mph and sounds like a thrumming (whoom......whoom....whoom) sound frequency is speed dependent is isn't noticed below 40 and is less noticeable but still there above 60. I think higher frequency masks it as well as lower. I'm wondering how changing the arms would cause this? Jacking with the Quattro somehow. Really NOT thinking it's tire related or cv or bearing. Right front tire just changed due to bubble and same noise. Also narrowed it down to right front issue as it becomes more prevalent on left turns which work right suspension. Gets quieter on right turns that force weight to left side. I changed the arms myself and am not above saying I screwed something up, I just don't know what...HELP! Oh additionally, I drove the car this morning in bad slushy weather on highway and it felt "not right". Like there is a problem with the all wheel drive system and the car just doesn't track as it should. All tires same size. Assuming all things were done correctly regarding tires, what might cause this? Thanks in advance..

mishar

Sounds like a wheel bearing (not necessarily the right one), but it can be tire too. Try rotating wheels first.

Not tracking properly can be alignment, but also tires. Again rotating wheels should give a better picture, than go back to the alignment place and complain about that.

Matt Pizzola

Thanks. Not leaning towards bearing or tires as I've looked at that stuff pretty thoroughly. Still wondering if Quattro system can go wonky with arm changes somehow. Appreciate the advice.

mishar

Quattro system is actually very simple, almost fully opened all wheel drive transmission. Only specific is Torsen middle differential that is the lowest end of limited slip differentials. It has nothing to do with suspension and I can not imagine anything going wrong with it while replacing upper front links.

On the other hand wheel bearing is one of the trickiest problems sometimes overlapped by a tire problem. Sound is similar, travels and echoes around so it is hard to detect real source. It changes with speed and load, but not as simple as right turn + louder = left bearing. Those bearings has two plains of ***** and depending on which side is damaged the logic can be just the opposite. Bad alignment creates additional lateral forces that can make already damaged bearing louder. Again, replacing upper links can't make it worse, unless a big sledgehammer was involved.

SaltyIrishman

This may seem dumb, but double check that your wheel bolts are all torqued properly as well. I had a shop forget to properly torque one of my wheels on my old M5 and I got a very similar sensation to what you are experiencing. Thankfully the wheel stayed on.

MP4.2+6.0

Some already mentioned. What I would tend to eliminate is the control arm work, given you think you did it all correctly and parts are new.

1. I would thoroughly check tires and wheels first. Not just visually, but take them in for a fresh balance. Ask them to look specifically for anything out of round with either the wheel or the tire. As in, think bent wheel or broken tire internals, including main belt area (not just sidewalls). Could be multiple wheels from my own experience trying to run this same kind of thing down in the past. You can also try rotating backs to front as an indirect way to confirm the issue is in the wheels somewhere, if the rears are good. On my old A6, I ended up finding three of four wheels were slightly bent on close examination after years of use.

2. Think about tie rod end. It doesn't get at the source of vibration (like bad wheel, tire, balance, etc.) but if it is sloppy it lets it come through more. Having done them though, tie rod ends on D3 seem pretty robust, unlike various prior models.

3. Out of true brake rotor? Should feel in braking though too.

MP4.2+6.0

+1 on that idea too. BTDT when I forgot torque wrench step (on C1).

TSHong

Need to clarify if it's a noise vs a vibration you are feeling or both. If it's a noise it sounds like aright front wheel bearing. If you are felling a vibration at certain speeds, i would look at the tires for out of round, balancing, and or bent wheels.

No as far as the vehicle not tracking well, you mention you replaced the right front tire. If there are decent tread depth difference, that might cause you to feel like it's not tracking well.

Matt Pizzola

Thanks a lot guys. All good stuff. I think I will do a rotation as that hasn't been done, only the tire replacement. It is possible I suppose that the alignment specs used to set to are not correct. Can anyone tell me what they should ideally be on my car? It is definitely a vibration more than a sound and pretty sure it is in the wheel. Tried to eliminate brakes and trans best I could. Wheel lugs are good but good call. Hoping rim isn't damaged and if it's the tire on the right front then I'd have to have two bad ones in a row. Tread isn't so far different. Once I can get a rotation and alignment I'll let you's know. Crossing my fingers. Thanks so far!

MP4.2+6.0

Alignment specs below.

From my last alignment right after the upper control arm change, I cross checked the printed specs against what their standard machine set up says on screen and in the print out. Their print out used the sport suspension spec, even though W12's are non sport; the only difference is in the camber anyway which is just for reference given what can and can't be adjusted. That is to say, for practical purposes what they pulled in the standard indy shop type set up with a decent laser based alignment was appropriate. Post alignment and post suspension work I am back to a very new car driving feel at 108K miles, so very happy camper with it now.