Yes, I have searched the forum for this topic. Yes, I have tried to follow advice given in those other threads. No, I have been unable to get any fluid to flow to the rear brakes. Here is the situation; power steering fluid was introduced to the brake master cylinder this past winter. I bled the system as best as I could given that it was ten below outside and I have no heated garage to work in. Anyway, the brakes worked fine until June when they would progressively get applied until they were cooking the rotors. All four wheels were hot after a short ten mile trip. The brakes would not release. I believed it was the abs causing the issue. I was advised that it may be all rubber components in the system had swollen due to the contamination. So, I replaced all calipers, all rubber brake lines, master cylinder and the abs module. With the rubber lines off, I blew brake cleaner through the lines to clear any contamination. With all lines cleaned, I installed all new calipers, brake lines, master cylinder (bench bled before installing) and an abs module from a salvage yard. $600 bucks into this and I didn't have another $500 for a.new abs module. I opened the abs control module and resoldered the connections that others have had problems with. Anyway, went to bleed the system, no fluid to the rear. Put a harbor freight vacuum pump to try and pull fluid to the rear, no go. Buddy gave his pressure bleeding system to use to try and force fluid through, again no fluid in the rear. I cracked the rear brake line at the abs pump to see if there was fluid coming out, nothing. I next thought the proportioning valve may have been tripped, so I pumped up pressure, cracked the front and reset the valve. I purchased the proportioning valve tool to hold the valve in place to allow the fluid to flow to the back. The valve ia centered (i can see it in the hole). No joy, no fluid to the rear. I purchased an upgraded code reader to auto bleed the abs. I have done so twenty times, still no fluid flows when I crack the rear line at the abs pump. I am out of ideas other than the salvage yard abs pump is bad. Anything else that could be the hangup and how to solve it?

Any help or advice is appreciated.

 

Forgot to clarify, the front brakes have fluid and work. There is no fluid leaving the abs pump to the rear.

 

After continuing to mess around with this problem, I think the proportioning valve may be the problem. I cracked the two lower input lines on the abs pump. The left one leaked fluid right away, the right side was dry. I cracked the lines coming from the master cylinder, both leaked fluid right away. So I am starting to think I do not have the proportioning valve centered or the valve is blocked or faulty in some way.

Any thoughts or suggestions?

 

If you have a scan tool to run the ABS in bleeding mode you should have fluid going to rear lines. Fluid has to leave the ABS pump to get to the proportioning valve.
Cracking the line at the proportioning valve inlet and no fluid is the conformation.

 

The fluid runs from the master cylinder to the proportioning valve, to the abs motor. At least that is what I see with my eyes.

 

Then I would suspect the proportioning valve for sure. Should have some fluid flow through it. It could have been bad for years but never noticed also.

 

Just wanted to post an update for future reference. I ended up replacing the proportioning valve. That allowed fluid to flow to the rear abs port and ultimately to the rear brakes. I was able to bleed the brakes and get them to work normally. This has been a major pain in the backside and the process severely strained my marriage, but I finished it for less than $1000 and now have an all new brake system on my suburban.

Would I do it again? Maybe, with the understanding that it will take a long time and strain your patience and the patience of your loved ones...

Hopefully, others will get some useful info from this post.

 

I am pretty much in the same situation you faced a couple of years ago. Replaced all the steel lines in a 04 Yukon and have used the “mighty vac” at the calipers in the rear, pressurizer system at master cylinder, & auto bleed using a scan tool. I’ve had no luck for almost a week in getting fluid to flow to the rear calipers. No problem in the front with flow, so I am pretty much at my wits end with a trip up to the mountains of Colorado tomorrow and I might just have to end up taking one of my other non-4 x 4 vehicles instead. Maybe I’ll give this proportion valve a shot here. Thanks