The proportioning valve's duty is to control/distribute the amount of pressure in system to the various wheels with front having around 60 % of the braking force.

Did you adjust the rear brakes shoes after replacement of the slave cylinders?
Does rapid pumping of brake results in pedal pressure/height?

Answered by KHLow2008 (expert)
39,832 answers provided

Yes it does but then it Goes back to nothing after letting it sit for a Few min. My Concern is the Load Sensing Valve on the Back axle. Could this be the Issue since when the Car is being Bled it is on a Lift but then on the Ground after that.

Response from Bill716
1 question asked

The load sensing proportioning valve is a height sensing valve mounted on the rear suspension that applies more brake to the rear when the back of the car/van is carrying a load, although I'm not aware of this car having one.

Answered by Wrenchtech (expert)
14,713 answers provided

It has one located on the Driver side of the axle. This was the initial Problem because it was leaking. We replaced it and since we have also Replaced the Master Cylinder and both rear wheel cylinders.

Response from Bill716
1 question asked

A faulty load sensing valve can cause low pedal positions but the symptoms you described seems to indicates system has air trapped or the brake shoes had not beed adjusted correctly.

Bleeding on lift or ground does not matter.

Answered by KHLow2008 (expert)
39,832 answers provided

Check the installation and adjustment. If it is not adjusted correctly, you can have either low pedal or stiff and inefficient braking. Adjustment has to be done with vehicle on ground.

Answered by KHLow2008 (expert)
39,832 answers provided

If you actually do have one, then you may have trouble bleeding if the car is in the air and the wheels are hanging free.

Answered by Wrenchtech (expert)
14,713 answers provided