Hi ! These effects are indeed computed in an analog mode based on the wheel slip (it's not on/off) so it's normal to get some slip when braking.
If you want something more "binary" you can use a higher threshold (it will cut all the smaller effects) and eventually a higher minimum force (so the motor will start stronger.
you can see the impact of each setting in realtime on the response curve :
Do not hesitate to use the record replay feature so you can replay game data and tune the settings to your will comfortably out of game : 
I've added a complete description of these settings here (write in progress): https://github.com/SHWotever/SimHub/wiki/ShakeIt-V3-Effects-configuration
Nicolas
Thanks for the swift reply. I guess I had figured that wheel lock was more of a binary thing - a wheel is either rotating or not. But I guess there's a middle zone of under-rotating.
I'm basically keen to have the motor on coinciding with when you get the audio cue in-game. It's the nature of my motors that any degree of spinning causes quite a pronounced vibration effect, so ramping it up from very early on doesn't really provide any useable tactile feedback because it's essentially on all the time under braking irrespective of wheel lock.
I'll have a go with the settings you mention. A question about those parameters: what do they relate to? For example is threshold the threshold of wheel-lock or braking force? And same for min force: is that min force of wheel-lock, braking or force of motor? All a bit confusing. And what are the axes of the response filter curve? Not sure what the x and y refer to.
This is my secondary set of pedals that I'm retrofitting. I have some Fanatec clubsport v3's with the vibration effect built in and found them so easy to get going the way I described above. So diving into all this parametric and response interface has been in comparison quite a learning curve!
Thanks again for the help.
Sorry to be reviving an ancient thread, but I'm having some trouble configuring my brake pedal wheels lockup rumble for Dirt Rally 2.0. I have the motors connected to an Arduino with motor shield, and in other titles I seem to be able to configure it properly so that the pedal rumble activates in the correct situations.
But in DR2 it seems to only respond to the "trigger when brake pedal reaches %", and starts rumble at that point no matter if the wheels are locked up or not. Rest of the settings are default.