I just realized that the best way to get a car to braking/let-off drift is to increase rear balast. Take the Mustang Cobra R, for example, it would not braking drift. So I added 100kg of balast and moved it all the way to the rear, and viola!! Braking and let-off drifting was now easy.
Note on Balast: Changing balast position will have no affect if there is no balast to move. In other words, the higher the amount of balast weight, the more affect moving it will have on the car. Just for compairison, I moved it all to the front and could no longer get the car sideways. All the way to the rear and the once understeering car was now loose as a goose and harder to control. TRY TO MAKE THE CAR NEUTRAL. A loose car is hard to control and a tight car is hard to get sideways, A NEUTRAL CAR IS EASY TO GET SIDEWAYS AND EASY TO CONTROL.
Also, adding rear balast will increase forward bite in a rear wheel drive car, making it harder to get wheelspin. Likewise it is recommended to only do this with high powered cars. However, the increase in rear momentum will usually overcome the increase in rear tire grip.
Also, (this should be obvious) adding balast will slow the car down on the straightaways, so use it wisely.