What does the proportioning valve do? Mine on my 5 isn't hooked up to anything and I can't find anywhere it hooks up too... It just has a wire dangling from it. Also, I have manual brakes, so does the proportioning valve have something to do with power brakes? I don't understand it!!!
It is a "Combination valve: and has two functions:
- Pressure differential valve and sensor
- Rear brake proportioning valve / metering valve
The front and rear circuits pass through this combination valve from the two sides of the master cylinder.
If the pressure falls in one side, like a rear brake line failure, a light will come on the dash. You can continue on your journey with one circuit as the master cylinder has two sides to it. This switch is hydraulically resetting.
The wire you have found used to go to the warning light.
The proportioning part / metering valve is to provide less pressure in the rear circuits than the front, otherwise it will tend to lock the rear wheels and go into a skid. To this end it will as far as I understand interrupt the increase in pressure build up in the rear lines. There is a plunger on the side to hold it open whilst bleeding the brakes.
It is fitted to manual and power brake systems.
If yours is not fitted it will decrease the effectiveness of the brakes in hard braking conditions.
Whether you need a warning light is debatable but it is just above the temperature gauge in the central cluster.