Originally Posted by fleetsidebob
In the PU I'm building, I'm using a GM master cylinder / power brake booster that has a factory combination valve. I would like to plumb an adjustable proportioning valve (APV) somewhere in the rear brake line.
Can I remove the combination valve entirely and run the brake lines directly to the master cylinder?
Any suggestions or recommendations on where to install the APV?
There are advantages to using the combo valve like having a brake pressure differential warning light, and the combo valve gives you a convenient way to plumb the lines to the calipers/slave cylinders instead of cobbling together something from the brass fitting drawer. So what I recommend is to first try the brakes w/the combo valve installed as-is.
If you find the combo valve's brake bias to the rears gives TOO MUCH rear brake, simply install the adjustable prop valve in the line from the combo valve going to the rear brakes.
If you find there's NOT ENOUGH rear brake, just adding an adjustable prop valve will not help because you can only take bias away
from the rear brakes because of the combo valve already has a rear brake proportioning valve in it. In this case, the combo valve's prop valve needs to be disabled. This will give full MC line pressure to the rears. You can try it this way to see if an adjustable prop valve is needed.
If you find that an adjustable prop valve is needed, put it somewhere easily accessible. Just aft of the combo valve in the rear brake line is a good place in most cases. If you decide not to use a combo valve, the choice is yours- but close to the MC would be my choice in most cases.
a thread on the subject that should be some help, there are others if you do a search of the site.
To answer your question, yes, you can plumb the brakes from the MC and eliminate the combo valve. Use fittings to divide the single ports into two lines; do the rears back at the axle housing like the factory does. The fronts can be split where ever it's convenient. Keep it neat, pay close attention to making good flares- that causes more problems than anything. Don't forget to bench bleed the MC. Be sure the caliper/slave bleeders are on top