Well the greatest is probably an a compound. One thing any system is going to need is line pressure. Going to a compound like a “a” will compensate for a low application psi but it will also wear fast. Possibly in a few hundred miles or less. I have found that the “e”compound from willwood has great wear characteristics and will last over a 1000 miles in race conditions. But it grabs far less then a stickier compounds.
I use to used that dual master cnc pedal assembly. The results were exactly like you say. It would not stop well. I can see how you would not be able to hold it back in your situation. To fix this I ditched the cnc master cylinders and build my own pedal assembly that works with a stock ford master cylinder and vacuum booster. I used a inline pressure valve to create differential brake bias. And two electric vacuum pumps for the boost as the engine has to much cam. This totally fixed the line pressure issue and now my truck stops. This could have done this with a hydro booster too but I didn’t want to take any oil from the steering system.
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This a pic of the pedal system looking up. There’s a “L” rocker in there that converts pedal “push” to a cable that runs across the back side of the tire wall and wraps around the passanger side to the back side of the cab. This cable uses a pulling force to actuate the booster and master.
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Back side view of the pedal assembly from the seat.
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This is the vacuum booster and master cylinders. It is hidden behind the passenger seat. The white bottle is the fire bottle. The pull cable clearly seen in this pic. The system need two vacuum pumps to work right. The only better way to do this would be use a hydraulic booster from a diesel one ton truck. I could still do that but I don’t want have volume and pressure issues then with the steering pump. My pumps not that big.
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The truck. Before I did this it would not stop with any amount of confidence. Poor would describe the truck stopping ability with the cnc dual master assembly. Now it stops. Even with the “e” compound pads.
Btw, all the stock parts are “unmolested stock 1995 f-150” parts that can be found in any auto parts store on either side of the boarder. If some thing breaks with the booster or master cylinder, autozone will have it.