Yes it matters. The bore size is different to accomidate the needs of each brake setup. The bore for the front brakes is usually bigger as the front calipers need more fluid volume due to the bigger pistons.
Also, I plumbed my cobra M/C same config as my thunderbird's m/c WAS which ended up with the 12mm going to the rear brakes and the 10mm port going to the front... shouldn't this be backward if what you say is true? And of course the important question before I make my new lines... IS it backward?!?
Ok, I think I know what you were saying.... one bore but two valves...? But it is my understanding that a properly functioning M/C should have equal pressure at each port. Anyone else have input?
Yes in theory a properly functioned MC should have equal pressure.
However, i do not know if reverseing the ports will mess with the shuttle valve located inside the factory combination valving. The shuttle valve shuts off pressure to front or rear brakes in case of a massive leak. I would assume it would function the same however.
The lines need to run to the combo valve anyway, so does it really matter if they are reversed or not. If you are bypassing the combo valve....well that's just unsafe.
Also, you say the shuttle valve inside the combo valve cuts off pressure when there is a leak but does this even continue functioning with a gutted valve?
I just read up on combo valves, and this may be wrong, but it seems that it doesn't cut pressure in the event of a leak but has a valve that flips a switch in a car that has a low pressure light in the dash...?
But it seems the important function of the combo valve is that is engages the rear brakes slightly sooner than the front brakes to keep the car on a straight path going into braking.
The combination valve is a proportioning valve and shuttle valve in one
On the Mustang, the proportioning valve is in the front part and is usually removed with aftermarket brake setups to distribute equal pressure to both ports and is adjusted via an aftermarket adjuster.
The shuttle valve shuts off pressure to either rear or front brakes in the case of a massive leak (hit debris which slices a brake line) Basically with near equal pressures, the valve stays centered, but if there is an imbalance, the shuttle valve slides over and severely restricts flow to the side with lease resistance (where the leak is)
It doesn't work with small leaks. Only really works if a line completely opens.
The stock 3-port fox MC blows ass. One line runs direct to the front left brake while the other 2 lines go to the prop valve and are split between the rear brakes and front right brake.
With a 2-port MC, you can set the brakes up the way it "should" be. Both lines run down to the gutted combo line and both front brakes T into the combo valve with a single line going to the drums with a proportioning valve installed at the brass union on the firewall.
1. Never had the 'standard fox 3 port' - I got a REAL car that came with 4 wheel discs (except I hated the abs )
2. Hey dreamz, open your eyes and read my sig! I have 275's WITHOUT flipping my quads (and could still fit 10.5's with even bigger meats BEFORE modding the quads!) eat that! lol, jk... Thanks for the info everyone...