Rear brake line wierdness

[svdsinner]

I've just finished replacing the rear drum brakes on my '01 2500 Cummins RWD and went to bleed them.

Oddly, no matter how many pumps on the brakes, no fluid was coming out of the bleeder valves. The reservoir is filled with new brake fluid, and while my buddy pumped the brakes, I could see a few bubbles coming up through the reservoir, but nothing came out the back.

I followed the rear brake line from the drums to a T fitting, and from that T fitting to a device that has a lever with a rod going down to the rear axle. (Is that something that changes rear brake pressure depending on load?)

I decided to remove the line going to the front to see if the fluid was making it there. The tube that leads into that device was corroded and disintegrated as soon as I turned the flange nut.

Obviously, I need to replace that, but something is still weird. There is no sign of leaking fluid on that pipe and pumping the brake didn't shoot fluid out of the opening.

I checked the rear line under the hood next to what I think might be an ABS valve. (It is at the end of the run from the rear part of the truck. I'm open to the possibility that the ABS stuff is messing with my troubleshooting, but I don't know how.) Brake fluid leaked as soon as I started to loosen the flare nut, so brake fluid was making it that far. But if there is a leak between there and the back, why wouldn't pumping the brakes squirt fluid out of the leak? (The reservoir is still within a few millimeters of the level it was at before I pumped the brakes dozens of times, so no fluid is leaving the system.)

What is my next step to finding out why brake fluid isn't making it to the rear of the truck?

(Not sure if this is possible, but is there a front/back valve the previous owner could've turned to 100% front to avoid fixing the rear brakes? )

 

[GTyankee]

One thing that you might check is the Proportioning Valve

You may even want to buy an Adjustable Proportioning Valve

This is from another Dodge Forum, it sounds like they had the exact issue that you are having
.............................................

So, I took my truck to a local shop to have the front brakes checked out since they were getting hot, smoking and sticking. While I was having the brakes checked out, I asked them to go ahead and flush the system. While they were checking they system to see what was causing the issue, they found that the rear brakes weren't getting any fluid. They traced it back to the proportioning valve saying that the valve was allowing fluid to go to the front brakes, but not to the rear. But they also said that since the ABS is in the rear, replacing the valve would be a job for the dealer since the ABS module would have to be messed with in some shape or form.

Its possible that it would have to be messed with...
For instance If you are bleeding your brakes you may need a scan tool to activate the servo motor in you ABS unit to clear all the air from the system. I only have rear wheel abs in my 96 but disconnected it anyway due to the motor leaking.
As for the proportioning valve...
Its used to shut off fluid to the rear to prevent skidding out and causing you to lose control. If your rear brakes aren't getting fluid then only your fronts are stopping which would cause excessive glazing and front brake failure. You may want to sand your pads and maybe get your rotors cut.

You may need to rebuild or replace the Brake Master Cylinder, if the things listed above don't work

 

[svdsinner]

Looks like the truck has an electronic proportioning valve.
Does anyone know how they work:
Are they on/off or proportional?
Is the signal just 12v or a PWM signal?

I'd like to try making an electrical tester to send it signals to test if it is working, but I don't know what I should be sending it. (I'm a decent electronics hobbyist so making something to spoof a PWM signal or on/off signal wouldn't be too hard.

Also, if it turns out to be bad, is there anywhere to get a replacement? I searched online but the only proportioning valves that I see are manual, not electronic.