Please tell me if this is needlessly complicated and/or just plain stupid.

Ive seen some cars that from the factory, use a combination proportioning valve that splits each of the 2 circuits coming from the master, then does the pressure metering for the rear, and feeds the brakes diagonally. The idea being that if you lose pressure somewhere, like say from rupturing a brake hose at one wheel, you will still have one rear brake and one front brake. This seems like it would be much safer than potentially losing both front brakes if you were to blow out a hose on that circuit.

Heres a shitty mspaint diagram in case I dont make sense

 

I found a couple "dual bore" prop valves that look to be designed specifically for what Im describing.

AP:
https://apracing.com/race-car/actuat...-bore-cp4550-1



Pro-S:
https://www.pro-s-fittings.co.uk/pro...32185113542691

 

Theory is sound but what happens when you're bleeding the brakes and you have one person open a bleeder valve? Pedal still goes to the floor right? It could be a lot of effort to do all that if it turns out that when you rip a brake line off you only get maybe 5 to 10% braking power in the remaining circuit, which is not going to be enough to keep on the track anyways if the brakes fail.

 

That makes sense. By the time you realize what is happening and then remember you can pump the brakes, youre already in the tire wall.

 

Only way that works is with a twin master cylinder setup like a Tilton. I had the Wilwood 1" tandem M/C when I had a catastrophic front hub failure. Brake caliper departed with the wheel. I only log front brake pressure, but it dropped to 0, the pedal was on the floor, and the front reservoir was empty.
I don't know of any track that, assuming your were near the limit during the failure, had enough room to safely slowdown with <50% braking force. Sure there are some random corners at tracks with a bit of runoff, but that's down to shear luck. And that half of the system still functional is going to try to rotate you quite spectacularly.
I think you'd have better luck with a lot less effort by just keeping the e-brake. It was useful driving my car onto the trailer(after slapping on a new hub), and back into the garage.

 

Thank you for the feedback. By tandem MC Im assume you mean a proper bias bar type setup?
That would really be the ideal way to go.

Based on what Im hearing here, I think its safe to assume that a dual circuit OEM type master only manages to provide a little bit of brake pressure in the event of losing one circuit. Enough to improve safety on the street but useless on the track.

 

This was my setup:

I've since retrofitted NB2 ABS, but the concept is the same.

Automotive Brakes: How Does a Tandem Master Cylinder Work?, by Curtis Jacobson

During my actual failure it's difficult to say that I was actually getting rear brake torque. I wasn't in a braking zone and I didn't go hard on the brakes, because it was at Gingerman and there's almost nothing you can hit (aside from the pit wall). The car was also engine braking and LF was sliding on the front bumper, so it was slowing down pretty quick.

The main benefit to the dual master, as opposed to a tandem, is that you can use a balance bar to adjust the F:R pressure ratio, which works through the pedal range. You can also size the front and rear pistons differently. Unlike a rear only balance adjuster(shown above) that really only works at mid-high line pressures, so you have to dial in trail braking balance other ways.