J-440, what I told you about the brake line routing for the two different M/C's is correct. You can double check me by going to the Wilwood website and looking at the blueprints. I've sold several hundred of the old style M/C's and a handful of the new style.
Hold off is a delay in sending pressure , typically to the front brakes which allows the rears to apply first. This helps prevent locking up the front brakes when first hitting the pedal.
A residual pressure valve is mostly used for when the M/C is below the height of the calipers or wheel cylinders to prevent back flow of fluid. They used to be installed inside old drum brake M/C's to prevent the cups in the wheel cylinders from leaking from having no pressure on them. At rest the brake shoes are against a stop and there is no pressure in the system. When disc/drum combos became more popular, the OEM's removed the residual pressure valves from the M/C's and used expander springs in the wheel cylinders. A residual pressure valve added into a brake system may also help mask brake pad knockback to a degree. Knockback typically happens with fixed calipers and the rotors have an amount of run out - they push the pads away from the rotor which can cause a low pedal on first application
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