I have a 1990 Tracker with the rear brake proportional valve. My question is: Is this rear brake proportional valve really needed or can it be bypassed? The one that is on my Tracker is a little rough and I am not sure if it is working or not. The service manual says it is used for brake valving when the rear cargo area is filled with weight. Based on the amount of weight in the cargo area the prop valve changes the braking to the rear wheels. Does this actually work and does it make a big difference? Can I bypass it? 
Thanks in advance
TL