Hi all, I am new to the forum.

I've had my '01 A4 2.8 Quattro Automatic/Tiptronic since May 2005. After about one year, I started noticing a slight popping/thumping sound when going from coasting to acceleration, mostly at low speeds. Doesn't have to be hard acceleration, but just going from coasting (where the wheels are pulling the engine) to acceleration (where the engine is pulling the wheels), creates the thump. In addition to hearing it, I can also “feel” that something goes "thump" somewhere, but can't really say where it comes from. Also hear/feel the same thump when coming to a stop (while the car is downshifting from 2nd to 1st , I think). I can avoid this particular symptom by coming to a stop very fast (braking hard) or veeeery slowly. Worst case in manuevering around parking lots at very low speeds, 1st and 2nd gear, and ther problem is gone at hogh speeds, 3, 4, 5th gears.

About 1.5 years ago, the Audi dealership mechanic claimed he did not reproduce the "thump" during a test-drive, which first really annoyed me, however after picking the car up I noticed that the phenomenon doesn't really show up until after the car has been running for a little while (5-10 mins). It's like there is a slack somewhere in the drive train that only shows up after the car is warm. I’ve been living with this condition now for about 1.5 years, but it annoys me a lot, and I’m wondering if it’s hurting the transmission, as it seems to get a little worse over time. It’s got 75k mi on it now, and is otherwise in great condition.

Recent work: Just changed the ATF, no change in symptom. Just reset the ECU/TCU (off battery overnight) no change in symptom (except now I need my friggin' radio code again, which I don't have).

Other possible leads: bad torque converter.. not spinning up properly at low speeds maybe... at high speeds there are no problems... so it seems when certain parts of the drive trains are turning fast, the required slosh effect is still there to provide smooth transition from coasting to acceleration.Sticky solenoid inside transmission... causing pressure buildups to slow, causing the transmission to "grab" hard and with a slight delay... creating the thump? Dirty intake sensors... confusing the TCU with bad/incorrect readings, causing the delay + thump?

Any tips?

Thanks,
Einar

 

Bad motor mounts? Universal joints?

 

well that was definitely one of my first guesses way back, but the dealership stated "all mounts OK" about 1.5 yrs back. Of course, I haven't had a second opinion on that. Can bad mounts explain the temperature dependency?

 

I have the same problem with my 99 A4-V6 Quattro auto.
It seems only happened when going from coasting back to acceleration. May be when the lock up torque converter is unlocking. I am suspecting low transmission fluid but you've proved that it was not the case.
It is quite annoying and my wife has ref
I saw other owner has the same problem too but no one has replied.

 

I have the same problem exactly as you described in the first post!

IDK what is is this is my second audi and it both audi had same thing...

 

Same here too guys, although I have noticed it even at high speeds if I am coasting going slightly downhill and approach an uphill grade, when I start to accelerate it will sometimes clunk when it shifts down to 4th.

 

Clunking from the drivetrain in our cars is most commonly a loose subframe, it becomes loose after a few wheel alignments. The bolts for the subframe should be replaced everytime they are loosened but no one ever replaces them, so they turn themselves loose. It also explains the heat theory because it would be come easier to move the frame when its hot.
Other than that replacing the snub mount, transmission mounts and motor mounts are the only other causes.

 

got a pic?

 

Of what, the subframe? Look under the car, its the huge cradle holding the trans and engine up.

 

Happens on my 5MT as well, same thing. When its cold outside and I hop in the car, it seems nice and tight, but after a nice cruise its clunking like nuts!