Hi all,

My 2004 Passat 1.8t 4Motion is starting to show a few problems, first, my input shaft bearing is noisy with the clutch pedal released, I only hear it with the window open but it's probably not a good sign. Second, when it's cold it grinds going into 2nd and 3rd gear (Gets better after driving for a while and the fluid warms up, I've tried replacing the fluid but it only helped marginally). I also get this weird noise in first gear and I have no idea if that's normal, I've heard everything from it makes that noise because of it's tight gearing to that one of the gears are chipped.

Overall, I think my transmission is going to go out at some point, I do want to keep and mod this car. Rebuilding would cost more than I paid for the car, so I think I'm better off doing a swap. Problem is, manual Passat transmissions are super rare, especially 4Motion, finding one is gonna be tough. Audi A4 Quattro 01A's, however, are much easier to find.

My 01A has a code of PHH, there's a listing for an Audi 01A with a code of FNU for example. The only differences between them that I know of are that the axle flanges are different (which can be swapped) and that the final drive is different (3.70 vs 3.89), which makes me wonder if that's compatible with my rear diff.

So, can the swap be done? Is the rear diff compatible with any final drive or is it matched to the transmission?