Trouble bleeding rear brakes

[jos51700]

I just swapped a blown axle out of a '93 Dakota for a junkyard unit. The junkyard unit has 9" drums, the recipient was 10" drums, but I had already sealed the cover before I realized that, so I just swapped drums and axle together. The system is rear abs with booster.

I can NOT get brake fluid to the 'new' wheel cylinder bleeders. I have fluid at the rear junction block, on both sides, but it's not making it any further. I've taken the bleeders out and blown through them, and they're clear. I've tried using a mighty vac, plenty of the brake pedal pumping with opening and closing the bleeders, and nothing. The brake pedal was pushed while the line was off, so the master was low, but it never ran out of fluid and I didn't think I would get fluid at the distribution block if the master has air in it.

Am I missing something in the swap from ten to nine inch drums? I drive it and it stops fair enough as is, but I haven't done drums in a decade and I feel like I'm missing something. I really don't think both lines could be plugged, and there's no visible kinks in either line.

Suggestions?

 

[Professor Fate]

Look on the left rear side leaf spring- there is a secondary "load sensing" proportioning valve, with two lines in (from the front main prop valve) and one line out to the axle/splitter fitting.
The intent is that there are two different pressures coming from the front prop valve, and the secondary valve selects between them depending on cargo weight to achieve adequate braking.
TOSS THAT SOB. They have been known to seize up and stop functioning, and replacements are impossible to find.
To do this, you need to follow the two feed lines to the front (main) prop valve, disconnect one of the lines (high pressure, but I forget which one it is- it's been a while) and plug that port. Remove the disconnected line and secondary prop valve, and connect the remaining pressure line to the line going to the splitter.
I'll bet now you can bleed the brakes decently.
Not an exact picture, but it will give you an idea what you're looking for:

 

[jos51700]

Look on the left rear side leaf spring- there is a secondary "load sensing" proportioning valve, with two lines in (from the front main prop valve) and one line out to the axle/splitter fitting.
The intent is that there are two different pressures coming from the front prop valve, and the secondary valve selects between them depending on cargo weight to achieve adequate braking.
TOSS THAT SOB. They have been known to seize up and stop functioning, and replacements are impossible to find.
To do this, you need to follow the two feed lines to the front (main) prop valve, disconnect one of the lines (high pressure, but I forget which one it is- it's been a while) and plug that port. Remove the disconnected line and secondary prop valve, and connect the remaining pressure line to the line going to the splitter.
I'll bet now you can bleed the brakes decently.
Not an exact picture, but it will give you an idea what you're looking for:
View attachment 1716427793

I don't remember seeing that when I was swapping the axle, but was looking at the axle, not at leaf springs. I'll check it out. Thanks!!

 

[jos51700]

Look on the left rear side leaf spring- there is a secondary "load sensing" proportioning valve, with two lines in (from the front main prop valve) and one line out to the axle/splitter fitting.
The intent is that there are two different pressures coming from the front prop valve, and the secondary valve selects between them depending on cargo weight to achieve adequate braking.
TOSS THAT SOB. They have been known to seize up and stop functioning, and replacements are impossible to find.
To do this, you need to follow the two feed lines to the front (main) prop valve, disconnect one of the lines (high pressure, but I forget which one it is- it's been a while) and plug that port. Remove the disconnected line and secondary prop valve, and connect the remaining pressure line to the line going to the splitter.
I'll bet now you can bleed the brakes decently.
Not an exact picture, but it will give you an idea what you're looking for:
View attachment 1716427793

I'm not seeing anything related to the load sensing mechanism. Just a regular leaf spring...

 

[Professor Fate]

I'm not seeing anything related to the load sensing mechanism. Just a regular leaf spring...

Driver's side, near the front spring eye, if I remember correctly.
It could very well have been removed already...

 

[jos51700]

Driver's side, near the front spring eye, if I remember correctly.
It could very well have been removed already...

I'll double check

 

[jos51700]

Ok, so no load sensing stuff is present.

I'm getting brake fluid at the junction block, just can't get it to the bleeders

 

[Bewy]

Brake lines might be rusted internally, blocking flow.