I have yet to try (waiting for the update on ORBX), but the modelling changed (you should check out the mega thread (https://forums.flightsimulator.com/t/released-aeroplane-heaven-spitfire-mk1/) for any discussions about it.
The Spitfire does not have brake pedals, it has rudder and a single brake, it has some form of differential braking, this is done by pulling the main brake and then deflecting how much pressure is applied by the rudder pedals.
Have you tried pulling the brake and then deflecting with the pedals? (this is how the real aircraft works) and I believe this is how its now modelled (until enough air is over the rudder to actually do anything useful).