I'm running a Wilwood adjustable with all my other Wilwood stuff. Plummed to the rear, just turn the knob to adjust the range from a 0-60% decrease in pressure. Even with 4 wheel discs you should always use a proportioning valve, weight distrobution, tires, suspension, they all contribute to how the cars stops and how weight is distributed when you do stop. The valve allows you to adjust the bias to the individual car.
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Who cares how much horsepower it has, all that matters is how fast it goes!
Best run 13.23 at 106.97mph with a 2.183 60' Times from before tune and driver mod.
Tad, I have a question for you. I always thought that the reason for the duel bowl mc is that the front and rear were isolated making them safer than the "fruit jar" single bown mc. But I have also noticed that when bleeding brakes and opening the bleeder screw the pedal goes straight to the floor, thus loosing all braking. Why then is the duel bowl mc safer? Kip
If you have a leak in a single-bowl m/c system, you're pretty much screwed. You can try to pump the pedal to keep forcing fluid into the system in an attempt to bring pressure back up, but that only works if the leak is minor and only until you run out of fluid. Fluid pressure is the same across a closed system, and if fluid pressure is zero, you have no brakes.
In a dual-bowl m/c you have two systems using separate fluid, but linked hydraulically. During normal operation, without any proportioning or metering valves, pressure remains the same throughout both systems. The catch is, there's a mechanical backup in case one system loses pressure (I left this out earlier, as it didn't apply to the discussion at that point).
For example: In our case, the rear piston in the m/c operates the front brakes and the front piston operates the rear brakes. If you have a leak in the rear braking system, the rear piston (which operates the front brakes) pushes the front piston (rear brakes) all the way to its stop, then starts building pressure in the rear piston (front brakes). You'll have a very low pedal and might have to pump it a little, but you'll still have front braking power. You'll also set off the brake warning light which is triggered to come on if the pressure varies too much between the two braking systems. Low pedal, bright red brake light, most people can figure out that the brakes need to be serviced.
If you lose pressure in the front braking system, the rear m/c piston isn't able to build pressure. In this case the rear piston moves forward until the piston extension, a small rod at the end of the piston, contacts the front piston and starts pushing it forward. Again, you'll have a very low brake pedal which may require a little pumping to bring it up, but you'll at least have rear braking power. And again, you'll set off the brake warning light.
First of all, the FLUID is isolated between the front and rear braking systems, pressure is not. There are two pistons in the m/c. They are connected hydraulically, not mechanically. The pedal rod pushes on the rear piston which builds pressure in the front circuit which then pushes on the front piston to build pressure in the rear circuit. It's still a single closed fluid circuit. If you lose pressure in either circuit, you're losing pressure everywhere. Pascal's law: fluid pressure in a closed system remains the same at all points within the system. This is why the pedal drops to the floor if you open one bleeder screw. The drop in pressure is spread across the entire system.
If the two systems were completely isolated, you'd never know if you had a problem with either system until you noticed a drop in braking performance. The pedal would remain the same as long as one one system was working properly. Obviously this would be unsafe, which is why braking systems are not designed this way.
Second, wheel cylinders requiring more fluid doesn't change the fact that they require less pressure. This is why there's a metering valve, to make sure you have some risidual pressure in the rear to keep the shoes close to the drums so you don't have the fronts contacting the discs long before the shoes touch the drums. You're not building much pressure anywhere until both pads and shoes are contacting their respective friction surfaces. And like I explained, pressure is constant throughout the entire system, so without some form of proportioning valve and metering valve, the drums are doing far more work as pressure builds than the discs are.
Third, none of what I said is incorrect. I generally try to be fairly nice to people here and give them a chance to understand why they're wrong, but you're all making it very difficult. A lot of engineering goes into designing a vehicle's braking system. If you don't understand in detail how a hydraulic braking system works, you shouldn't be modifying your braking system outside of the factory design.
I am installing disk brakes on the front and rear of my car. The front circuit is bled while the rear is not yet. There is about 1.5" travel at the pedal, before it is rock solid. So I had assumed that there is a mechanical connection between the two circuits, which I now realise there is, but that is only when the rear circuit is not functional.
I was largely incorrect in my post, as it applied to a non normal situation. Thank you for clarifying this point for me.
Tad, I have a question for you. I always thought that the reason for the duel bowl mc is that the front and rear were isolated making them safer than the "fruit jar" single bown mc. But I have also noticed that when bleeding brakes and opening the bleeder screw the pedal goes straight to the floor, thus loosing all braking. Why then is the duel bowl mc safer? Kip
If you have a leak in a single-bowl m/c system, you're pretty much screwed. You can try to pump the pedal to keep forcing fluid into the system in an attempt to bring pressure back up, but that only works if the leak is minor and only until you run out of fluid. Fluid pressure is the same across a closed system, and if fluid pressure is zero, you have no brakes.
In a dual-bowl m/c you have two systems using separate fluid, but linked hydraulically. During normal operation, without any proportioning or metering valves, pressure remains the same throughout both systems. The catch is, there's a mechanical backup in case one system loses pressure (I left this out earlier, as it didn't apply to the discussion at that point).
For example: In our case, the rear piston in the m/c operates the front brakes and the front piston operates the rear brakes. If you have a leak in the rear braking system, the rear piston (which operates the front brakes) pushes the front piston (rear brakes) all the way to its stop, then starts building pressure in the rear piston (front brakes). You'll have a very low pedal and might have to pump it a little, but you'll still have front braking power. You'll also set off the brake warning light which is triggered to come on if the pressure varies too much between the two braking systems. Low pedal, bright red brake light, most people can figure out that the brakes need to be serviced.
If you lose pressure in the front braking system, the rear m/c piston isn't able to build pressure. In this case the rear piston moves forward until the piston extension, a small rod at the end of the piston, contacts the front piston and starts pushing it forward. Again, you'll have a very low brake pedal which may require a little pumping to bring it up, but you'll at least have rear braking power. And again, you'll set off the brake warning light.
Thank you.
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1968 Mustang Coupe, Warm 289 C-4 Auto, 2nd owner.
quote:
ORIGINAL: Scott H.
buying an '08 GT to commute with is like killing flies with a very expensive shotgun.
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RE: Disc brake swap proportioning valve options - 
