FrankenBrakes Questions

[clazer]

The frame and drivetrain under my 1972 Jimmy are a cut down 1996 GMC Yukon 2 door. The truck runs, but nothing was done cleanly by Dr. Frankenstein, the previous owner. As such, I get to do a lot of reading to figure out repairs. This site has been great, but I can’t figure some things out.

I replaced the front discs with 6 lug 3/4 ton hardware.
Installed all new drum hardware in the rear (it’s an 11” drum 10 bolt).
New master cylinder. Existing vac boost.

I have pulled and bench bled the master cylinder multiple times with the same result: brake gives decent resistance after install. I go to bleed the rear brakes and get no pressure to the rear cylinders. Basically the only fluid that comes out of the bleed nipple is just gravity fed. Then my brakes are soft and just go to the floor. There’s enough to soft-stop using the front brakes, but it’s not driveable.
From what I can tell, the ABS module is there but I don’t see an abs dump valve unless it’s integrated somehow. I’d like to just bypass the ABS module, but none of the guides on here seem to match what I have. What recommendations do you have? Is the abs dump valve already bypassed and the proportioning valve is bad? Something else? Thanks for reading and have a great day!

Also, yes, there’s plenty of other issues in the pics as well, trying to take care of them one at a time!

 

[clazer]

Better pics of the abs module

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[GoToGuy]

Wow, just wow. Am I missing something , I don't see a proportioning valve.

 

[clazer]

Wow, just wow. Am I missing something , I don't see a proportioning valve.

I don’t either and was hoping someone could verify for me. Any idea what it’s supposed to have in it? Current output is separate lines for the front and a single bigger line for the rear. Go straight to the brakes after the ABS unit. Would partially explain why I had to buy a drum puller to remove the left drum.

 

[Schurkey]

I hope the diagnostic link connector is in place and wired-up/functional.

Bleed the ABS using a scan tool to chatter the valves. Then bleed the wheel cylinders/calipers again. See what happens.

 

[clazer]

I hope the diagnostic link connector is in place and wired-up/functional.

Bleed the ABS using a scan tool to chatter the valves. Then bleed the wheel cylinders/calipers again. See what happens.

The port is wired up- I’ll see if my little scanner has that capability. Was thinking I’d just remove the ABS module completely and find a suitable proportioning valve.

 

[clazer]

I’m ordering this and throwing the ABS in the junk pile.

JEGS 631302: O.E. Style Proportioning Valve/Distribution Block GM [for Disc/Drum Applications] - JEGS

OE Style Proportioning Valve/Distribution Block

www.jegs.com

 

[someotherguy]

It was my understanding that the 1995-up style 4WAL unit has all the components self-contained. I see in your pics it appears not all the connectors are hooked up to it, which could be an issue. I don't know much about that setup though as most of my trucks have been the older RWAL setup which has the external combo valve and dump valve.

Example.. here's a pic of my old 1995 3500HD. 4WAL controller in view, master cylinder as well, and no separate combination valve or ABS dump valve under the m/c in the usual place we see them on earlier RWAL trucks:

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And a '94 3500HD with the expected arrangement of combination valve and dump valve under the m/c, and RWAL controller box to the side.

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In fact I just found an excellent side view of parting out a '98 C3500 - you can see the 4WAL module connected to the master cylinder and no other external devices in sight.

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I knew my memory wasn't failing me on this one.

Richard

 

[clazer]

Richard, that’s really helpful- looks just like your first pic. So that ABS box does everything- control, combine, dump.
You are right, I disconnected the electrical after bleeding the brakes.