Millerbt

Hoping someone else on here has experienced the same problem, which has so far stumped the dealership and 2 euro-oriented independent shops.

2002 A4 1.8T Quattro, 180k miles

There’s a clunking noise and pulsating entire car shuttering, almost like the car is coughing, only under these conditions:
· The car is in drive.
· The car is coasting in drive, or applying minimum acceleration to maintain a speed.
· The car is hot (has been driven more than 30ish miles on the highway).

Check out this video of what it sounds like:

This condition is worst when going downhill and when turning left. I get a fairly consistent clunk every 1-2 seconds when at its worst. It doesn’t appear to be speed related but more load force related (doesn’t happen under acceleration).

If I’m doing a lot of highway driving, it’s very pronounced. If I haven’t been on the highway for several days, it’ll go away completely. It also doesn’t happen if the car is coasting in neutral.

I’m unable to recreate the noise by driving tight circles at a slow speed in either direction.

Having replaced spark plugs, coils, fuel injectors, engine wiring harness, air filter, fuel pump, fuel sending unit, fuel filter, and cleaned MAF – it does seem the car vibrates more than it should at idle and in gear.

I jacked up all 4 wheels individually and confirmed the ball joints, control arms, tie rod ends, brakes, and steering rack are all tight and with the exception of steering components, are fairly new. Put the car in neutral and spun the wheels, but am unsure if the noise the front wheels make is normal.

Check it out in this video:

I’m hoping to narrow the causes down before I go sinking money into drivetrain parts. It seems like these symptoms match up with some others have had with a bad center bearing.

One of the indy shops wants to replace the driveshaft ($2,800ish) and suggested the problem may be in the front diff/trans and need a replacement ($6,500ish – not gonna happen). Twice previously they looked over the car and suspension and said everything is okay. They originally diagnosed this problem as a vacuum leak and plugged catalytic converter.

Dealership looked over the car and says the drive shaft, axles, and suspension are all good after they replaced motor mounts.

lyleswk

If it were the center bearing, you should have a lot of play in the driveshaft. If you don't, then...

Can't help but think it may be the Torsen diff since it sounds like a bearing and does the same from both sides. Not ever heard of one failing in my time on the this or other forums. Can you not tell if the source of the noise is buried in the Torsen?

Millerbt

It sounds like it's coming from the diff rather than at the wheel. I'm going to look into a diff fluid change. Oil in there could be 20 years old for all I know. No leak, but I'd imagine the oil could be broken down and it seems to be brought on by heat. Around the city and for the first 30 or so miles on the highway the car runs great.

Millerbt

Time for an update!

Since the original post I've put another 1,500 miles or so on the car.

I took the car back to Audi and drove with a tech who immediately experienced the clunking. Without looking at it, he said he'd lean towards the center mount on the prop/driveshaft being bad. They couldn't get the car in the shop that day and I had to schedule an appointment for a few weeks later.

Fast forward a few weeks and the car went back to Audi. They had the car for 8 days, put a total of 50 miles on it, said their longest test drive was 20 miles, and claimed the same tech test drove the car the entire time and couldn't recreate the problem. When I informed them I was picking up the car, they apparently took it out on a short drive, recreated the problem, diagnosed it as an unknown transmission problem and quoted me a new transmission for about $4,700.

I drove the car round trip about 400 miles over the Thanksgiving holiday and it exhibited all the same symptoms mentioned in the original post. When I returned from that trip, I finally found a way to recreate the clunking when stationary. I can only get it when I put the car in reverse with the emergency brake set and my foot on the brake and try to drive away. I should have recorded a video when I first discovered this as the clunk was exactly as I described above - a consistent clunk every second or so.

That was about a week ago. The weather where I live has turned colder and I'm back to regular (less than 25 miles per weekday) driving. My problem has nearly disappeared. I just recorded a video of me trying to drive the car with the brakes on. The clunk I'm describing is near the beginning, where you see the engine shift forward and stutter before buckling down and continuing. I can't get it to do this in drive - only reverse.

Reverse/Drive Stationary Video

Any more thoughts?

Millerbt

It ended up being the transmission. Had it replaced with a used one 70k miles its 190k chasis junior. Runs great now!



I'd also replaced the drive shaft, both front axles, and transmission mounts to no avail. Chalking it up as a lot of preventative maintenance.



Thanks to all who offered their help!