Novak GTB brakes

[frogger]

I've just installed a new Novak GTB and 6.5 sintered in my B4. It goes like a rocket but I am having serious problems with the brakes. The brakes seem to have no modulation - just on or off. So when I apply brakes, even a tiny bit the rear end just swings around.

I use a KO Esprit III, Spektrum module, have tried everything I can think of: the KO Thottle:Brake from 0-100 in all settings (improves it a tiny bit but not much, brake expo down to 50%, set the GTB minimum brake to the 1st setting, etc.

I've also softened the suspension a bit, added lead weight behind the rear bulkhead.

Any ideas?