Haven't dismantled the valve on a hydro master cylinder, but I did take apart the proportioning valve on the standard 89 master cylinder, and it can be easily gutted.
Then again, I may just leave it; the stock brakes worked just fine with the truck unloaded. The reason I did the conversion is due to coming about 2" from shortening a VW bus when the ******* decided to cut in front of me and make a panic stop when I had the 5er in tow. It now does a considerably better job of bringing my 18k pounds of junk to a halt...And I give the yahoos in front of me more room.
And you already moved the pushrod pin higher on the pedal, correct? If so, leave things as is. Read Jaluhn83's post from yesterday and consider these three scenarios:
1) hydroboost master, factory pedal - starting from a stock system simply swapping to the larger master cylinder you lose mechanical advantage because larger masters make less pressure pers force applied. The volume pushed out per inch of stroke OTOH increases - the volume required to actuate your brakes is constant, so you need less stroke to get there, resulting in higher pedal.
2) factory master, hydroboost pedal - by moving the pedal pin closer to the pedal pivot you increase the leverage your foot has on the master cylinder, thus you have more apply force on the master that could be used to produce higher line pressure out of the factory master. You pay for this in pedal travel, the piston stroke does not change but the higher leverage requires you to push the pedal down further to make the same stroke at the master.
3) hydroboost master and pedal - this is the effects of #1 and #2 combined, and cancelling each other. The higher apply force by the modified pedal makes up for the increased piston area of the hydroboost master, and the master's shortened stroke makes up for the increased travel of the modified pedal. You end up with similar line pressure and pedal travel as before, only now the hydroboost linkage does not bind.
This is all with the engine shut off, and booster reserve charge depleted. The reason why hydroboost brakes make more line pressure at the brakes once engine is running is because (when compared to a vacuum booster) the hydroboost can ADD more force to what you provide thru the pedal and the pushrod. Modify your PS pump for higher line pressure, and the hydroboost can now add even more force. But shut the engine off and deplete the booster reserves, and they ain't all that different from one another.
You're currently at #2, you're making the highest line pressure possible but you're pay for it by having to push the pedal a bit further down. By swapping to the hydroboost you will get the shorter pedal travel, but your line pressure will drop - in other words you will get improved pedal feel, but you'll pay for it in lower line pressure, resulting in lower clamping force at the calipers and shoe-pushing force at the wheel cylinders. If you're OK w/ your pedal travel and feel now, leave the system be, you're already maxed out in what you can put down at the wheels.
Does that make sense? I can provide calculations if needed...
