"BRAKES"
Dissertation by JB. Based on a little research and some of my experiences
(real and observed) at Bonneville, Maxton and El-Mirage.
1) Metering Valve - The metering valve is required on cars that have disc
brakes on the front wheels and drum brakes on the rear wheels. The metering
valve compensates for this, making the drum brakes engage just before the disc
brakes. The metering valve does not allow any pressure to the disc brakes
until a threshold pressure has been reached. The threshold pressure is low
compared to the maximum pressure in the braking system, so the drum brakes
just barely engage before the disc brakes kick in.
If you're running a Disc / Drum brake combination you need a
metering valve end of story.
2) 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
of 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. Typical brake bias on a stock car is 75% front
and 25% rear.
There a several ways to solve this problem. A) A proportioning valve. B) Two
master cylinders, one for the front brakes and one for the rear brakes. C)
Different sized caliper or wheel cylinder pistons, front and rear.
On my Hondaliner I took the third approach. The front calipers are larger and
the rears are smaller and it works very well, with no signs of locking up or
any other braking problem.
3) Combination Valve - Factory piece combining the Metering and Proportioning
Valves in one unit. Probably not the best system if you're 'modifying' brakes
for a race car.
|