Differential Problem? Audi A3 2.0 TDI Repair

Hello,

Unfortunately, my A3 has been "acting up" for the past few kilometers. It's an Audi A3 2.0 TDI (engine codes BKD, GRF) with over 305,000 kilometers on the clock.

"For about 2000 kilometers, he's been hearing noises coming from the engine compartment, and they're getting louder. They seem to be coming from the lower area of the driver's footwell, on the left side! Sometimes the noises get louder, and the car starts to vibrate. The car is undrivable and makes a huge rumbling sound! This is especially noticeable when the engine is warm, like during a highway drive. When the engine is cold and has cooled down, it seems to be okay again, but the noises persist."

Here are some more details...

* The engine is running perfectly, with no error messages and all readings within normal limits.
* New tandem pump and cleaned PDEs... (approximately 5000 km)
* The suspension is in good condition, with no worn or damaged components.
* Clutch and dual-mass flywheel are approximately 20,000 km old.
* Constant velocity joints (CV joints) and their rubber boots are sealed and in good condition.
* Tires are balanced and the suspension is measured.

Okay, now let's move on to the description of the error.

* Vibration and shaking in the steering wheel; speeds above 120 km/h are impossible.
* Metallic knocking sound, especially when turning at low speeds and with the steering wheel turned, and it gets worse when the car is warmer. The possible steering angle decreases as the car gets warmer!
* Starting at 90 km/h, you can feel a vibration in the steering wheel, which gets worse as the speed increases.
"Above 120 km/h, there's a significant rumbling noise, as if it's only running on 3 cylinders... you have to stop the journey."
* Everything is independent of the engine speed, and disengaging the clutch has no effect...
* Sometimes there's a cracking sound coming from the transmission when I shift between first gear and reverse.

I already took the car to the workshop, and the mechanic did a test drive, but it was probably the placebo effect – he didn't notice anything! Unfortunately, I then had to travel abroad, where everything got worse. I suspect it's the differential!

Do they perhaps have any idea what it could be?

I just want to be able to "reliably" get home and not necessarily break down on the road. I think I could get used to a used replacement gearbox!

Sure, here is the translation of the text from German to English:

"LG" is an abbreviation for "Liebe Grüße," which means "Best regards" or "Best wishes" in English.

I initially typed 'transmission mounts' and 'engine mounts,' but you're saying...
that disengaging the clutch makes no difference.

When was the oil level in the transmission/differential last checked or changed?
Because 305,000 kilometers is quite a lot of mileage.
Does it have original performance, or was it adjusted/modified 250,000 km ago?

Hello,

"First of all, thank you for the quick response! The mileage is original; however, the cylinder head was replaced at 180,000 kilometers."

Similarly, the transmission oil was changed approximately 20,000 km ago, along with the clutch and the dual-mass flywheel.

The transmission is dry, so everything should still be in the green zone, more or less!

Is there a way to check the engine mounts? If they were worn, wouldn't the clutch "decouple" the problem?

Sounds like a driveshaft issue. Have those been checked yet?

@charmillo
The mileage is original.

I mean the engine power. Maybe it's been heavily modified with a chip.
Of course, this will have a brutal impact on the lifespan of all the components in the powertrain.

Hmmm, the drive shafts seem to be in good condition... smooth operation and no cracking! These are still the original ones; I only replaced one bellows about 20,000 km ago because it was torn.

What was also surprising to me was that the jerking started about 3,000 km ago... it would occur intermittently for about 4-10 km and then disappear. At first, I thought it might be a failing particulate filter (DPF).
I was able to eliminate some of the rumbling by giving it full throttle, which put pressure on the transmission...

That's why I went to the workshop, and they didn't find anything.

Now I went abroad, and it just kept getting worse... And what's making me suspicious is that the noises are coming from the left footwell, right where the transmission is!

Oh yeah, it's not chipped... it's got the standard 140 horsepower!

I'm surprised that the noises in the workshop weren't noticed.

I would proceed as follows:

- Test drive on a two-post lift to listen for noises in the transmission and suspension, etc.
To pinpoint the source of the vibrations more precisely.

- If necessary, obtain a camera and inspect the riveting of the toothed wheel, as well as the condition of the bevel gears.

Hello,

First of all, thank you for the tips; I'll start next week. I just hope that I can somehow find my way back home.