Passat AWD Transmission Failure: Causes & Repair

Hello fellow DIY enthusiasts,

Recently, something very unpleasant happened to me. I own a 1998 Passat, a 1.9 TDI Syncro. About a week ago, I was driving uphill in fourth gear when suddenly I heard a rumbling noise, a slight jolt, and the fourth gear disengaged. All the other gears still worked normally. So, I took it to a trusted mechanic...

The result was:
We've never seen anything like this before..., we have no idea what it is..., VAG no longer repairs transmissions..., a replacement transmission costs approximately 3500,- €.

Shock!
Of course, I couldn't accept that, so I started looking online for companies that repair transmissions (with a warranty).
The friendly mechanic took that with interest, removed the transmission, and now it's with a transmission specialist. It will cost approximately €1100-1300.
I called today to find out what was broken and what might have caused it.
According to the mechanic (who seemed knowledgeable), the gear from the 4th gear has exploded on the shaft teeth and broken into 5 pieces. He mainly sees this kind of failure in modified TDI engines. So, it's a complete fracture caused by excessive force. This car has a 01A transmission, with the identification number DGW. This transmission was originally designed for a gasoline engine and was later adapted for use with a diesel engine (with a different gear ratio).
It is designed for approximately 260 Nm.
I don't know how many Nm my AFN produces because there wasn't an all-wheel-drive dynamometer available. I've only driven it for 90,000 km.

What do you think about this situation? Has anyone else experienced something similar? What would you do with the tuning?

I believe this is an unfortunate incident and doesn't necessarily have to happen again.
Or is this gearbox perhaps undersized?

Hi,

Quote:

The result was: We've never seen anything like this before... we have no idea what it is... VAG no longer repairs transmissions... a replacement transmission costs approximately €3500.

Why then would you need a replacement gearbox? Perhaps because the old gearbox was actually repaired and then resold for €3500?

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

"Micha"

Sure. Somewhere, those transmissions are definitely being refurbished. But apparently, that kind of work is too time-consuming for a "regular" VAG workshop, and the warranty risk is too high.

Certainly the latter! Also, one shouldn't ignore the issue of profit. When I see that I'm getting discounts of 20% or more, and the dealer still isn't losing money on the deal...

I'm more interested in the connection between the broken gear and the tuning. I received a repair manual for the transmission today.
Looking at it, there's only one gear that could potentially be broken. All the other gears seem to be working. This gear is pressed tightly onto the shaft, so there's no play. I can't imagine that a gear would break just from normal acceleration (it wasn't full throttle). I've been modifying cars for 7 years now. Also, the torque on the output shaft (where this 4th gear sits) is significantly higher in the lower gears.

Okay, yes! The transmission needs to be refilled with oil. Does anyone have a recommendation for a good brand? VAG specifies: G 052 911 A SEA 75 W 90 (synthetic oil). The dealership would have to order the oil. If I buy it myself somewhere, it's probably cheaper and maybe even better?

Castrol TAF-X.

Regards,

Manuel.