Rear brake issue

[Robyn]

Well here we go again.
I need to do brakes on the remaining 94 Burb.
The fronts need one rotor and a set of pads.
The rear brakes dont seem to be working at all. Ride them hard and the drums dont even get warm. The shoes are fine.
I am suspect of the ABS system and or possibly the proportioning valve and the regulator valve.
I dont know if the thing has a height valve or not. its an 8600 GVW truck.
The thing has the 4WAL system. Even real hard pedal pressure wont cause the rears to apply enough to warm the drums up, ice cold. Hmmmmm something is amiss in river city.
There have been no codes on the system so its most likely not an electronic issue.
Any of you seen this type of failure??

[DmaxMaverick]

If you have no visible leaks, I'd suspect the MC first off. If you are applying pedal pressure, one (bad P-valve), or both rear brakes should be receiving some of it.

[Robyn]

I am thinking that the proportioning valve may be to blame. weather has been wretched and I need to work outside.
Im going to get the fronts back in good order and then worry about the rears.
has to be something that is restricting the flow of pressure to the rears for sure.
I will have to check the MC and see whats up. maybe crack a rear bleeder and see if I get anything and if not its got to be the P valve or the MC If it was an MC the light on the dash would come on signalling a loss of pressure in one system though????????