The Quaife sales literature shows the QDF6N as being used in the Z4. It would make sense I guess that bmw would have designed the front diff housing in the e53 around a diff they were already using. A smaller carrier, but that makes sense too in the sense front diff handles less torque in the x5.

I need to find that YouTube video again and see if he gives a parts list, where to buy the parts, and if I can see any shims, etc, come out when he disassembles it.

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Current
Original owner 2002 E53 X5 4.4i to 4.6i swap
2026 G80 M3 6 spd
2025 G06 X5 50e
Former
1972 Audi Fox
1986 Saab 900S
1996 BMW Z3
1998 BMW E36 M3 Sedan
2004 BMW E46 M3
2006 Audi A3 Quatro
1993 Mopar 318 Jeep Grand Cherokee
2015 V6 Jeep Grand Cherokee