The hotter GTIs use an electronically-controlled front differential — know which one you have, because they behave and fail differently.
XDS (all GTIs):
- XDS isn't a real diff — it's a brake-based system that nips the inside front brake to mimic a limited-slip. It's software; nothing to service, but it can't match a mechanical diff.
VAQ (Performance Pack — Mk7/7.5/Mk8):
- The VAQ is a genuine electro-hydraulic clutch-pack front LSD on Performance-Pack cars — it really helps traction and turn-in.
- It shares the transmission fluid — keep it serviced. Faults show as a diff/ESC warning and log on VCDS; a failed clutch pack or actuator is a gearbox-side repair.
Aftermarket: a mechanical LSD (Quaife / Wavetrac) is the upgrade for track cars on non-VAQ GTIs.
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