Since I've installed the softer rear shoes on the GN (all 4 shoes are large) it seems that if I don't really watch how I use the brakes, the rears lock up very easy. Is there anything to do to fix this, besides putting the stock shoes back in every time I'm not at the track? Maybe a proportioning valve?? If I don't use the soft brake shoes at the track, the 60' are in the 1.9's!