Anybody know?

 

"The proportioning valve reduces the pressure to the rear brakes. Regardless of what type of brakes a car has, the rear brakes require less force than the front brakes"
-howstuffworks.com

has somthing to do with the brake line diameter....i think a smaller diameter will have more "push". so it basically is the point where the brake lines seperate from front to rear, giving the rear larger ? diameter lines

 

samsonite?

 

Stolen from http://www.howthingswork.com

Proportioning Valve

The proportioning valve reduces the pressure to the rear brakes. Regardless of what type of brakes a car has, the rear brakes require less force than the front brakes.

The amount of brake force that can be applied to a wheel without locking it depends on the amount of weight on the wheel. More weight means more brake force can be applied. If you have ever slammed on your brakes, you know that an abrupt stop makes your car lean forward. The front gets lower and the back gets higher. This is because a lot weight is transferred to the front of the car when you stop. Also, most cars have more weight over the front wheels to start with because that is where the engine is located.

If equal braking force were applied at all four wheels during a stop, the rear wheels would lock up before the front wheels. The proportioning valve only lets a certain portion of the pressure through to the rear wheels so that the front wheels apply more braking force. If the proportioning valve were set to 70 percent and the brake pressure were 1,000 pounds per square inch (psi) for the front brakes, the rear brakes would get 700 psi.

 

I'm actually interested in how it works, not what it does. They don't really tell you. I don't think changing the line diameters would change the pressure.

 

it will effect pressure because the mc can only force oh so much out of it the thicker the lines the less it will force in

 

It would affect pressure if there was actually fluid flowing through the lines, but the flow is small when you first step on the brakes, and there is no flow once the brakes are pushed down. That's why I don't exactly get how it works.

 

Line diameter won't do it. It's piston area in each caliper that determines brake-force proportion. The piston area in back is smaller than the piston area in front, so the rear brakes provide lower force.

Actually, the proportioning valve is there to provide non-linear proportion. At low braking force, it doesn't do anything, and braking forces are simply from the ratio of caliper piston areas. When you push the pedal hard enough to activate the valve, then the rears get lower line pressure than the fronts so they don't lock up.

I haven't taken one apart, so I don't know exactly how it works. Probably something like a regulator.



[Modified by JimBlake, 9:27 AM 3/6/2003]