Question: I have an 03 Ford Expedition and I have been experiencing pulsating in the steering wheel, I have turned the front rotors twice and in no time they are back the same way. So, I replaced both the front rotors and calibers, and its still not right. When I was bleeding the whole brake system, I noticed that the rear did not bleed like the front did, the pedal did not go all the way down. My question is what determines the amount of pressure that goes to the front verses the rear? I think that my problem is that the rear brakes are not being applied enough, thus causing the front to work harder and get hotter than normal, causing them to warp easier.

Answer:

There is a proportioning valve ( or sometimes called a modulator valve
) which in modern vehicles is usually combined with the ABS functions.
It should be located immediately after the master cylinder and is
usually an aluminum block. Your brake system should apply more
pressure to the front brakes, which is where most of the braking
occurs. You can test function of the proportioning valve by doing a
low speed panic test and see if the front or rear brakes lock up
first. Do it in an empty parking lot and have someone watch from a
distance to see which wheels lock up. With ABS, it wont be easy to
see. I would say 20 – 30mph would be all the faster you would want to
go. Again, be careful, make sure the parking lot is empty.