Originally Posted by ss396si
What kind of adjustable distribution block do I need? The kind that replaces my excisting prop block or the one that goes behind it?
It will help immensely if you would give a complete run-down of just what you now have. Drum/drum, disc/drum, original master cylinder or aftermarket or from another vehicle, is it a fast take-up type, what type distribution block do you have, as in does it contain a prop valve (i.e. is it a combo valve), is the m/c above or below the brake cylinders, do you have any residual pressure valving installed?
If it's a combo valve w/a functional prop valve:
If you don't like the front/rear balance, and you were to add an adjustable proportioning valve to the existing combo valve, you would in effect be adding a prop valve to a prop valve. In your case (having too much rear brake), this wouldn't be an issue unless other changes to the brakes or weight distribution, etc. were to be made that required there to be more
rear brake pressure than the existing combo prop valve allows.
If you add an adjustable prop to the existing prop, you would not be able to bias the rear brakes to have any more pressure to them than the existing setting of the existing prop valve- all you could do would be to take pressure away from them. But as I said, in your case this isn't so much of an issue.
Should you want to disable the combo valve prop function:
On most GM combo valves, you can disable the combo valve's prop valve by unscrewing the fitting from the combo valve that has the rear brake line coming from it, then remove the (rubber or spring loaded metal) valve inside the body, then reattach the fitting.
So- in your case- I would keep the existing combo/distribution block and simply plumb in an adjustable prop valve aft of the existing block. Should the need ever arise that you needed more rear brake bias than the existing combo prop valve allows, you will need to disable it. I hope I didn't confuse you too much.