For QUAIFE ATB Differentials:
When running a QUAIFE ATB Differential in a standard transaxle gearbox, we recommend that you use whatever your vehicle's manufacturer recommends. The QUAIFE ATB Differential does not require any special lubricants.
When running QUAIFE gearbox internals and a QUAIFE ATB differential – we recommend FuchsTitan SYN5 75W90.
For a QUAIFE ATB differential, running in a rear axle – use a hypoid 90 or 75W90, as above.
For those applications that will accept a GL5 or SAE75W90 gear oil, we recommend and sell Silkolene SYN5 75W90 gear oil. We use Silkolene in all our own QUAIFE racing transmissions.